Please do not adjust margins “This document is the Accepted Manuscript version of a Published Work that appeared in final form in Catalysis Science & Technology, copyright © The Royal Society of Chemistry 2017 after peer review and technical editing by the publisher. To access the final edited and published work see: http://pubs.rsc.org/en/content/articlepdf/2017/dt/c6dt04729g Dalton Transactions ARTICLE Mononuclear ruthenium compounds bearing N-donor and Nheterocyclic carbene ligands: structure and oxidative catalysis Received 00th January 20xx, Accepted 00th January 20xx a a b a c c b H.-J. Liu, M. Gil-Sepulcre, L. Francàs, R. Bofill,* P. Nolis, T. Parella, J. Benet-Buchholz, X. d a,b a a Fontrodona, Antoni Llobet, L. Escriche* and X. Sala* DOI: 10.1039/x0xx00000x SINO POSES EL NOM SENCER DESPRES A SCI-FINDER ES MES DIFICIL TROBAR-TE www.rsc.org/ A new CNNC carbene-phthalazine tetradentate ligand has been synthesized, which under reaction with [Ru(T)Cl3] (T = trpy, tpm, bpea; trpy = 2,2';6',2"-terpyridine; tpm = tris(pyrazol-1-yl)methane; bpea = N,N-bis(pyridin-2-ylmethyl)ethanamine) in MeOH or iPrOH undergoes a C-N bond scission due to the nucleophilic attack of a solvent molecule, with the subsequent formation of the mononuclear complexes cis-[Ru(PhthaPz-OR)(trpy)X]n+, [Ru(PhthaPz-OMe)(tpm)X]n+ and trans,fac-[Ru(PhthaPz-OMe)(bpea)X]n+ (X = Cl, n = 1; X = H2O, n = 2; PhthaPz-OR = 1-(4-alcoxyphthalazin-1-yl)-3-methyl-1Himidazol-3-ium), named 1a+/2a2+ (R = Me), 1b+/2b2+ (R = iPr), 3+/42+ and 5+/62+, respectively. Interestingly, regulation of the stability regions of the different Ru oxidation states is obtained by the different ligand combinations, going from 62+, where Ru(III) is clearly stable and mono-electronic transfers are favoured, to 2a2+/2b2+, where Ru(III) is almost unstable with regards to its disproportion. The catalytic performance of the Ru-OH2 complexes in chemical water oxidation at pH 1.0 points to poor stability (ligand oxidation), with subsequent evolution of CO2 together with O2, specially for 42+ and 62+. In electrochemically driven water oxidation, higher TOF values are obtained for 2a2+ at pH 1.0. In alkene epoxidation, complexes favouring bi-electronic transfer processes show better performance and selectivity than those favouring monoelectronic transfers, while alkenes containing electron-donor groups promote better performance than those bearing electron-withdrawers. Finally, when cis-β-methylstyrene is employed as substrate, no cis/trans isomerization takes place, thus indicating the existence of an stereospecific process. Introduction N-heterocyclic carbenes (NHCs) are carbenes -neutral compounds featuring a divalent C atom with six electrons in its valence shell- contained within an N-heterocycle that are a. Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, 08193 Barcelona (Catalonia), Spain. E-mail: + roger.bofill@uab.cat, lluis.escriche@uab.cat, xavier.sala@uab.cat: Fax: 34 93 581 24 77 b. Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona (Catalonia), Spain. c. Servei de Ressonància Magnètica Nuclear, Facultat de Ciències, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, 08193 Barcelona (Catalonia), Spain. d. Serveis Tècnics de Recerca, Edifici P-II, Campus Montilivi, Universitat de Girona, 17071 Girona (Catalonia), Spain. † Electronic Supporting Information (ESI) available: Spectroscopic (NMR, UV-Vis), spectrometric (ESI-MS), electrochemical (CV, DPV, bulk electrolysis, Pourbaix diagrams), catalytic (manometries) and structural (X-Ray diffraction) data. See DOI: 10.1039/x0xx00000x excellent ligands for transition metal ions (M), forming rather strong M-C bonds and often stable complexes under ambient 1 conditions. AQUESTA FRASE TAN LLARGA EM COSTA DE LLEGIR, JO LA PARTIRIA EN DUES. Transition metal complexes containing NHCs have found multiple applications in important catalytic transformations, such as hydrogenation, transfer hydrogenation, water 2 reduction and water oxidation. When designing catalysts for redox processes, controlling the oxidative power and the accessibility and stability of the oxidation states involved in the catalytic cycle is of paramount importance for the selectivity of the catalysed PEL DALTON JO TREURIA AMERICANISMES IS HO DEIAXARIA TO UK reaction. In general, in the presence of electron-donating ligands (such as carbenes) high oxidation states of the central metal ion will be stabilized, and hence its redox potentials This journal is © The Royal Society of Chemistry 2016 Dalton Trans., 2016, 00, 1-3 | 1 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name 3 decrease, thus facilitating oxidative catalytic processes. Additionally, when a water molecule is directly coordinated to the metal centre, the redox properties of the complex will be affected by proton exchange. The successive 1e oxidations taking place are accompanied by a sequential loss of protons favoured by the enhanced acidity of the bonded aqua ligand. This phenomenon, known as proton coupled electron transfer (PCET), allows transition metals to achieve high oxidation states quite easily, since the successive loss of protons -going from the aqua to the hydroxo and finally oxo ligand- allows the 4 maintenance of the total charge of the complex. In addition Plus, the σ and π donation of the oxo ligand present at high oxidation state further stabilizes high oxidation states at the metal centre. Thus, promising examples in water oxidation 5 catalysis have been reported within the last 6 years with Ir 6 and Ru NHC complexes, most of which are monometallic, although a few ones are multimetallic. Interestingly, during the past years researchers have emphasized the distinctive and sometimes superior performance of bimetallic catalysts because of the possible cooperative interactions existing between both M-OH2 active sites thanks to their relative 7 disposition imposed by the bridging ligand. Also, Ru NHC complexes have also found relevant 8 applications in alkene epoxidation catalysis. A remarkable example is the use of Ru-aqua complexes with increasing number NHC units that stabilize the Ru(IV)/Ru(III) redox potential to a much higher extend than the Ru(III)/Ru(II) and thus favouring the disproportion of the Ru(III) oxidation state. As a consequence of this the Ru(IV)=O species becomes a powerful two-electron oxidant. This is interesting because it avoids radical reaction pathways associated with 1 electron 9 oxidation processes. This is particularly interesting for the olefin epoxidation reactions since it will favour a concerted 8 pathway that will generate a stereoselective product. Within this context, and given the feasible preparation of thermodinamically stable NHCs and the interest in using them as ligands in oxidative catalytic systems, we have synthesized and characterized a new tetradentate NHC ligand (1,4-bis(12+ methylimidazolium-1-yl)phthalazine; L1 ). This new ligand loses a carbine moiety upon reacting with Ru precursors generating the new carbine ligand 3-methyl-1-(phthalazin-1+ yl)-1H-imidazol-3-ium) L2 and 3-siopropyl-1-(phthalazin-1-yl)+ 1H-imidazol-3-ium) L3 (see Chart 1). trans,fac-[Ru(Me-L2)(bpea)X] 2+ 2, 2a ; n+ a+ (X = Cl, n = 1, 1 ; X = H2O, n = Un pel enrabassat PhthaPz = 3-methyl-1-(phthalazin-1-yl)-1H-imidazol-3-ium), + 2+ + 2+ + 2+ + 2+ named, respectively, 1a /2a , 1b /2b , 3 /4 and 5 /6 , which show interesting redox properties when employed in water oxidation and alkene epoxidation catalysis. A MI AQUI MI FALTA EL LLIGAND MES IMPORTANT DE TOT EL PAPER EL L2+ I L3+! PER LA NOMEMENCLATURA DELS COMPLEXES ES MOLT FARRAGOS AMB EL NOM COMPLET. L’ABREUJAMENT HO FAS MES FACIL. Chart 1. Drawing of the NHC (L12+) and N-donor (trpy, bpea and tpm) ligands proposed to be combined with Ru. R= Me o iPr. and evaluated its effect on the electrochemical properties and oxidative catalytic activity of the corresponding Ru-aqua complexes. Aixo no ho heu fet perque es trenca abans no? . Additional auxiliary ligands include: the meridional tridentate N-donor ligand trpy, the facial tri-N-dentate ligand tpm and the either meridional or facial one bpea (trpy = 2,2':6',2''-terpyridine, tpm = tris(pyrazol-1-yl)methane, bpea = N,N-bis(pyridin-2-ylmethyl)ethanamine); Chart 1). Due to the 2+ instability of L1 under the synthetic conditions employed, we have obtained the mononuclear complexes cis-[Ru(Men+ n+ n+ L2)(trpy)X] , cis-[Ru(iPr-L2)(trpy)X] , [Ru(Me-L2)(tpm)X] and 2 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins “This document is the Accepted Manuscript version of a Published Work that appeared in final form in Catalysis Science & Technology, copyright © The Royal Society of Chemistry 2017 after peer review and technical editing by the publisher. To access the final edited and published work see: http://pubs.rsc.org/en/content/articlepdf/2017/dt/c6dt04729g Dalton Transactions ARTICLE Results and discussion 2+ Synthesis of the ligand L1 . L1(Cl)2 and L1(PF6)2 were obtained following a one-step nucleophilic attack of 1-methylimidazole to 1,4-dichlorophthalazine (dcp) in DMF (Scheme 1). The insolubility of L1(Cl)2 in DMF allowed the easy isolation of the ligand by simple filtration and subsequent washing with diethyl ether (yield 75%). Subsequent treatment of L1(Cl)2 with a NH4PF6 saturated solution in MeOH allowed the exchange of the chloride by the PF6 counterion (L1(PF6)2). sharply decreases (up to only 5% of the expected value) when the 1 H NMR spectrum of L1(Cl)2 is recorded in methanol-d4 (Fig. 1b), showing the fast exchange rate of these acidic protons with the protic solvent. Figure 1. 1H NMR spectrum of L1(PF6)2 in acetone-d6 (a) and of L1(Cl)2 in MeOD (b). Inset: zoom of the aromatic region of L1(PF6)2. Scheme 1. Synthetic procedure for the synthesis of L1(Cl)2 and L1(PF6)2. 2+ 2+ Characterization of the ligand L1 . NMR spectroscopy for L1 has been carried out both in acetone-d6 (L1(PF6)2) and methanol-d4 1 13 (L1(Cl)2). Both 1D ( H, C) and 2D (COSY and HSQC) experiments were necessary to characterize the structure of the ligand in solution (Fig. 1 and Figure S1 in the Supporting Information). All resonances could be unambiguously assigned based on their integrals, multiplicity and the C2v symmetry of the ligand in solution. 2+ For L1 , both H9 and H10 (or H9’ and H10’) display a doublet of doublets with a mirror effect, which is in agreement with the typical 10 AA’BB’ (9 9’10 10’ in our case) pattern of this kind of systems, as shown in the inset of Fig. 1. The singlet appearing at very low fields in acetone-d6 (Fig. 1a) can be assigned to the imidazolic protons 6 and 6’ in accordance with the high electron-withdrawing effect of the two heteroatoms present in α, as previously reported for 11 similar ligands. However, the integral of this resonance at 9.9 ppm Suitable crystals for X-ray diffraction analysis were obtained by slow diffusion of diethyl ether into a solution of L1(PF6)2 in acetone (Fig. 2). It is worth mentioning that the steric congestion of both five membered rings with the central phthalazine moiety (specially protons H6’-H9’ and H4-H9, at 2.4-2.5 Å) place the three scaffolds in different planes, with the left-side imidazole ring 42.5° below the phtalazine plane and the right-side imidazole ring 44.3° above (Fig. 2+ 2). The ORTEP plot for the cationic moiety of L1 and the acquisition and crystallographic data for L1(PF6)2 can be found in Figure S2 and Table S1 in the Supporting Information, respectively. This journal is © The Royal Society of Chemistry 2016 Dalton Trans., 2016, 00, 1-3 | 3 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name PF6 1. Ru(trpy)Cl3 2. Et3N/LiCl 3. NH4PF6 ROH 80oC/16h N N N N N Ru Cl (PF6)2 1. AgBF4 O R 2. NH4 PF6 Acetone/H 2O N N N N N N 90oC/4h N N N 1a + (R=Me) 1b+ (R=iPr) N N Cl- 2a 2+ (R=Me) 2b2+ (R=iPr) N N N N Cl- L12+ PF6 (PF6)2 OH 2 Cl 1. Ru(tpm)Cl3 2. Et3N/LiCl 3. NH4 PF6 Figure 2. Mercury plot of the crystal structure of L12+. The hydrogen atoms at closer distances are shown as spheres, and the angles between the plane of two imidazoles and the phthalazine scaffold are included. Color code: nitrogen, blue; carbon, dark gray; hydrogen, light gray. 2+ Reaction of L1 with [Ru(T)Cl3] (T = trpy, tpm, bpea). Breakage of 2+ + 2+ + 2+ + 2+ ligand L1 and synthesis of complexes 1a /2a , 1b /2b , 3 /4 + 2+ and 5 /6 . Following previously reported synthetic strategies 7b,10,12 III reported by our group 2 molar equivalents of [Ru (T)Cl3] (T = 2+ trpy, tpm, bpea) were mixed with L1 , triethylamine (Et3N) as reducing agent and LiCl to ensure the presence of a labile site in the generated complexes, and refluxed in MeOH for 16 h. After hot filtration, addition of a few drops of a saturated aqueous solution of NH4PF6 to the crude solution and partial solvent evaporation under vacuum, a brown precipitate appeared in all cases. However, II despite bimetallic species with the general formula [Ru2 (T)2(μ3+ II 2+ Cl)(μ-L1)] or [Ru2 (T)2(Cl)2(μ-L1)] were expected, when the 1 obtained compounds were subjected to H NMR analysis, their resonances, integrals and coupling constants matched those of a mononuclear Ru complex. Furthermore, DOSY NMR experiments excluded the presence of mixed mono and dinuclear species. As an example, Fig. S3 in the Supporting Information shows the DOSY NMR spectrum for the mononuclear compound obtained after III reflux of [Ru (trpy)Cl3] with L1(Cl)2 in MeOH. 2+ Thus, although L1 shows excellent stability in air and also dissolved in acetone or methanol at room temperature, it decomposes when refluxed overnight in the latter, therefore 2+ pointing to a replacement of one imidazole ring of L1 by a methoxy group due to a nucleophilic attack of the solvent (Scheme S1 in the Supporting Information). This phenomenon has already been reported by other authors when using related tetradentate 13 CNNC ligands in similar conditions. Then, isopropanol, with increased steric hindrance compared to methanol, was also tested 2+ as solvent for the coordination of L1 to Ru. However, the same process happened, with decomposition of the tetradentate ligand and formation of a mononuclear complex (Scheme 2). As a result, + + the new ligands PhthaPz-OMe (L2 ) and PhthaPz-OiPr (L3 ) have 2+ been obtained from L1 (Scheme S1), which can only act as CN 2+ bidentate ligands towards Ru. The breakage of L1 can also be 2+ explained from an electronic point of view, since when L1 coordinates to a first electrophilic Ru(II) ion, there is a flow of electron-density from the ligand to the metal centre and, therefore, the nucleophilic attack of a MeOH or iPrOH solvent molecule becomes still more favourable. O R Ru H 2O N N O N N Ru N N N N MeOH 80o C/16h 1. AgBF4 2. NH4PF6 Acetone/H 2O N N N N N N 3+ 42+ PF6 (PF6)2 OH 2 Cl 1. Ru(bpea)Cl3 2. Et3N/LiCl 3. NH4 PF6 MeOH 80oC/16h N N N N Ru N O N N Ru 90o C/4h N N N N N N O 1. AgBF4 2. NH4PF6 Acetone/H 2O N N N N O Ru N 90oC/4h N N 5+ 62+ Scheme 2. Synthetic procedures used for the synthesis of 1a+/2a2+, 1b+/2b2+, 3+/42+ and 5+/62+. Note breakage of L12+ when refluxed in MeOH or iPrOH. 2+ As a consequence, due to the breakage of L1 in the conditions III 2+ used, we adjusted the [Ru (T)Cl3]:L1 molar ratio to 1.5:1 in order to maximize the yield of formation of the Ru mononuclear species. + II + Therefore, complexes 1a (cis-[Ru (PhthaPz-OMe)(trpy)Cl]PF6), 1b II + II (cis-[Ru (PhthaPz-OiPr)(trpy)Cl]PF6), 3 ([Ru (PhthaPz+ II OMe)(tpm)Cl]PF6) and 5 (trans,fac-[Ru (PhthaPzOMe)(bpea)Cl]PF6) were obtained in good yields. The subsequent synthesis of the corresponding aqua complexes involved the presence of AgBF4 in acetone/H2O, which promotes the decoordination of the chlorido ligand by formation of an AgCl precipitate and allows the coordination of a water molecule. After AgCl filtration, acetone was slowly evaporated under vacuum. The counter ion could be easily exchanged from BF4 to PF6 by adding excess NH4PF6(aq) into the aqueous solution, obtaining the whole set of Ru-aqua complexes [Ru(PhthaPz-OR)(T)(H2O)](PF6)2 (R=Me, 2+ 2+ 2+ T=trpy, 2a ; R=iPr, T=trpy, 2b ; R=Me, T=tpm, 4 ; R=Me, T=bpea, 2+ 6 ) as red (or brown) precipitates (Scheme 2). + 2+ + 2+ + 2+ Structural characterization of complexes 1a /2a , 1b /2b , 3 /4 + 2+ and 5 /6 . All mononuclear complexes have been characterised by spectroscopic (1D and 2D NMR) and spectrometric (ESI-MS) techniques and by elemental analysis (EA). 1 + In the H NMR spectrum of 1a (Fig. 3) the loss of the “ABBA” spin-spin coupling pattern perfectly agrees with the reduced 2+ symmetry of L1 after nucleophilic decomposition. Furthermore, the two singlets integrating three protons each at 4.78 and 3.47 ppm can be assigned to the methyl group of the intact imidazole ring and the methyl group of the new methoxy substituent formed, 13 respectively. Additional C NMR and 2D-NMR spectra allowed full assignment of all resonances (see Figure S4 in the Supporting Information). 4 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE 1 + Figure 3. H NMR spectrum of 1a in CD2Cl2 and its corresponding proton assignment. Figure 4. Selective 2D ROESY NMR spectrum of 1b+ in acetone-d6 and schematic drawing of the observed interactions. + 1 + As expected, a similar H NMR spectrum to 1a was obtained for + 1b . However, now the singlet at 3.47 ppm assigned to the methoxy + substituent in 1a is replaced by a doublet and a septuplet (at 1.09 and 4.54 ppm, integrating six and one protons, respectively) due to the presence of the isopropoxy substituent (Figure S5a in the Supporting Information). Furthermore, the integrity and purity of + + 1a and 1b was confirmed by EA and ESI-MS (Figure S8a-b in the Supporting Information). + + The chlorido compounds 1a and 1b display Cs symmetry in solution, with the symmetry plane passing through the PhthaPz+ + OMe (1a ) and PhthaPz-OiPr (1b ) ligand, the Ru centre, the + + chlorido ligand and carbons C(27) (1a ) or C(28) (1b ) of the trpy ligand, interconverting the two sides of the molecule. Thus, with respect to the relative position of the chlorido ligand in relation to the Ru carbene bond, both the cis and trans isomer could be + + formed either for 1a or 1b . However, only one isomer was + + obtained in the reaction crude for both 1a and 1b , as determined 1 by H NMR (Fig. 3 and Figure S5a). 2D ROESY NMR spectra were then carried out to identify the cis or trans nature of the obtained + compounds. As shown in Fig. 4 for the 1b case (see Figure S5e for + the ROESY NMR spectra of the aromatic region of 1b ) strong interactions were observed between the isopropyl group and H24, H27 and H28 of the trpy ligand as well as between the methyl group of the imidazole ring and H21 of the trpy ligand, which clearly allow + the identification of the cis disposition of the 1b complex. The same conclusion could be extracted from the ROESY NMR spectra + of 1a (Figure S4e), and therefore the only obtained isomer is also 13 cis in nature. Again, additional C NMR and 2D-NMR spectra + allowed full assignment of all resonances of 1b (Figure S5 in the Supporting Information). With regards to 3 , due to the C3 symmetry of the tpm ligand, which coordinates in a facial manner, no isomeric mixtures are 1 expected. This has been corroborated by its H NMR spectrum (Figure S6a). The C1 symmetry of the complex converts the whole set of protons in different resonances and a complex spectrum is obtained. The assignment of each resonance to a single proton and carbon was carried out by 2D NMR experiments (HSQC, HMBC, + ROESY and TOSCY), while the integrity and purity of 3 was confirmed by EA and ESI-MS (see Figures S6 and Figure S8c, respectively, in the Supporting Information). + Concerning 5 , due to the flexibility of the tridentate bpea ligand, able to potentially coordinate the Ru metal ion either facially 14 or meridionally, seven stereoisomers could be potentially formed when combining bpea with the non-symmetric bidentate CN ligand 15 PhthaPz-OMe (Fig. 5). The notation fac and mer refers to the facial or meridional disposition of the bpea ligand, respectively, whereas up and down indicates the relative orientation of the ethyl group of bpea with regards to the chlorido ligand upon coordination. In the fac complexes, the cis/trans notation refers to the position of the chlorido ligand with respect to the aliphatic N atom of the bpea ligand, while in the mer cases the cis/trans notation refers to the position of the chlorido ligand with respect to the carbene atom of the PhtaPz ligand. Both steric and electronic interactions between the ligands coordinated to the Ru metal ion play a key role in the degree of the isomeric mixture synthetically obtainable. However, + in the synthesis of 5 , only the trans,fac isomer is formed (see below). Hydrogen bonding interactions between the protons in α to the pyridylic nitrogens of bpea and the chlorido ligand dramatically stabilize the trans,fac conformation, lowering the energy of the system. This strong stabilitzation for the trans,fac isomer has already been reported and thoroughly studied by means of 16 theoretical DFT calculations for similar Ru-based systems, and the predominance of these hydrogen-bonding interactions over other factors for stabilizing and selectively obtaining the trans,fac isomer in a series of related complexes has been already established by 17 several research groups. Furthermore, it has also been reported the preference of bpea for the facial coordination upon heating 14 (thermodynamic conditions). This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 5 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name Figure 5. Possible diastereomers for 5+. The PhthaPz-OMe ligand is represented as a CN connector for the sake of clarity. SENSE ESPAIS + Effectively, the trans,fac nature of the 5 complex was confirmed by selective NOESY NMR experiments, whose key interactions unambiguously revealed its stereoisomeric nature (Figure S7e-f in the Supporting Information). Thus, interactions between H1 and H20-H21 and between H18 and H34 are observed, confirming its trans,fac configuration. In consequence, analogously + 1 to what happened with 3 , no symmetry is observed in its H NMR spectrum (Fig. 6). Finally, the assignment of each resonance to a single proton and carbon was carried out by 2D NMR experiments + (HSQC, ROESY), while the integrity and purity of 5 was confirmed by EA and ESI-MS (see Figures S7 and Figure S8d, respectively, in the Supporting Information). Figure 6. 1H NMR spectrum of 5+ in acetone-d6 and its corresponding proton assignment. + Suitable crystals for X-ray diffraction analysis of 5 were obtained by slow diffusion of diethyl ether into a solution of the complex in methanol (Fig. 7), and a selection of the more relevant bond distances and angles is reported in Table S2. An ORTEP plot for the cationic moiety of this complex as well as that corresponding to its unit cell can be found in Figure S9 of the + Supporting Information. Thus, 5 crystallizes in a small unit cell containing two PF6 anions located in its centre and two independent complex molecules, each one located on each side of the PF6 anions. Additionally, a complete description of the acquisition and crystallographic data can be found in Table S3 of the Supporting Information. Figure 7. Mercury plot of the crystal structure of the cationic part of 5+. Hydrogen atoms have been removed for the sake of clarity except those involved in hydrogen-bonding interactions with the Cl- ligand. Color code: nitrogen, blue; oxygen; red; chlorine, green; carbon, dark gray; hydrogen, light gray. Atoms appearing in Table S2 or throughout the text are depicted as spheres that have been labelled accordingly. The Ru(II) ion adopts a distorted octahedral geometry with bond distances and angles that resemble those of analogous 15b,18 complexes reported in earlier literature. The Ru carbene bond distance (1.962 Å) is shorter than the Ru-N bonds, which are comprised between 2.0 and 2.1 Å. The N1-Ru-Cl (171.63°), N2-Ru-Cl (94.92°) and N3-Ru-Cl (90.90°) bond angles clearly confirm the facial coordination of bpea to Ru. Plus, the Ru-Cl bond appears trans to the aliphatic N atom of bpea, confirming again the trans,fac + nature of 5 . Furthermore, the imidazole and the phthalazine rings do not lay exactly on the same plane. Instead, there is a torsion angle of 16°. However, this angle is obviously shorter with regards to the one observed for the free ligand, which is around 43° (Fig. 2). The methoxy group is nearly on the same plane of the phthalazine skeleton, since the observed torsion angle C18-O-C14-N5 is only 1.9°. Finally, the N1-Ru-N3 and N1-Ru-N2 angles are, respectively, 81.15° and 81.68°, away from the 90° for an ideal octahedral geometry, due to the formation of two five-membered rings when bpea coordinates to the central Ru ion. In addition, clear hydrogenbonding interactions are observed between the pyridyl protons of bpea on C20 and C34 and the chlorido ligand (2.7 Å). This electronic interaction is responsible for the strong stabilization of the trans,fac + 16,17 configuration of 5 , as stated before. Replacement of the chlorido ligand by a water molecule in this family of complexes induces significant chemical shift + 2+ 1 displacements. This is exemplified by the 1a /2a H NMR comparison shown in Fig. S10, where mainly protons close to these monodentate ligands such as H22, H26 and H27 are affected. Similar displacements of the chemical shifts were obviously + 2+ observed for the very similar 1b /2b couple, and both complexes maintain their cis conformation after the coordination of the aqua ligand (see Figures S11 and S12, respectively, for a full NMR 2+ 2+ assignment of all proton and carbon resonances of 2a and 2b ). 2+ 2+ Complexes 4 and 6 also maintain their original conformation in solution after chloride displacement, as can be deduced from the NMR spectra shown in Figures S13 and S14 in the Supporting Information, respectively. Furthermore, the integrity and purity of 6 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE all four aqua complexes was confirmed by EA and ESI-MS (Figure S15 in the Supporting Information). Electrochemical and spectrophotometric characterization of + 2+ + 2+ + 2+ + 2+ complexes 1a /2a , 1b /2b , 3 /4 and 5 /6 . CV and DPV techniques have been used to determine the electrochemical properties of all complexes. The CVs in dichloromethane of + + + + complexes 1a , 1b , 3 and 5 are depicted in Figure S16 in the Supporting Information. All chlorido complexes exhibit a single III II reversible wave corresponding to the Ru /Ru process. The redox + + potentials vs SCE are very close for 1a (0.79 V) and 1b (0.78 V) given the high structural and chemical similarity of Ru in both meridional complexes, while a clear downshift of E1/2 is observed + + for the facial derivatives 3 (0.71 V) and 5 (0.68 V). This is in agreement with the higher σ-donating and lower π-acceptor + + capacity of both the pyrazolyl rings (3 ) and the aliphatic N (5 ) with regards to the pyridyl units of the trpy scaffold. The observed decrease in the redox potentials lies within a 70-110 mV range and is in agreement with previous results obtained for analogous Ru 15b carbene complexes containing trpy or bpea. The redox behaviour of the four Ru-OH2 complexes has been extensively investigated in aqueous media and their redox potentials and pKa values are summarized in Table 1, together with those of related aqua complexes containing the bpy ligand instead of the carbene bidentate scaffold for the sake of comparison. Table 1. Redox potentials (V) vs SCE and pKa values of complexes 2a2+ to 62+ and related aqua complexes where the carbene bidentate scaffold has been replaced by bpy. E1/2III/II Entry pH 1 1 2a2+ 2 2b 2+ 3 42+ 4 a E1/2IV/III iv/ii E1/2III/II pH 7 ∆E1/2c E1/2V/IV b Ref. pKa1 pKa2 3.0 11.5 0.74 0.50 0.52 0.73 0.49 0.51 0.48 0.03 --- 2.8 11.0 d 0.62 -- --- 0.35 --- 1.33 1.8 11.2 d 62+ 0.61 0.42 0.52 0.32 0.20 1.28 1.2 11.7 d 5 [Ru(trpy)(bpy)(OH2)]2+ 0.81 0.55 0.62 0.49 0.13 --- 1.7 9.7 19 6 [Ru(tpm)(bpy)(OH2)]2+ 0.70 0.55 0.71 0.40 0.31 --- 1.9 10.8 20 0.70 0.40 0.46 0.34 0.12 --- 1.2 11.1 21 7 a [Ru(bpea)(bpy)(OH2)] 2+ 0.49 0.03 1.29 d 0.1 M triflic acid. b phosphate buffer solution (µ = 0.1 M). c ∆E1/2 = (E1/2IV/III - E1/2III/II). d This work. III At pH 1, a single reversible wave corresponding to the Ru II OH2/Ru -OH2 process is observed for all aqua complexes (black lines in Figures S17, S19, S21 and S22 in the Supporting Information), in which again a cathodic shift of E1/2 (110-130 mV) takes place when introducing the facial ligands (entries 3-4 vs. entries 1-2, Table 1), following the same trend observed for the Ru-aqua complexes bearing bpy instead of the bidentate carbene ligand (entries 5-7, Table 1). At neutral pH, two very close redox processes separated by only 2+ 2+ IV 30 mV can be observed for 2a and 2b , corresponding to the Ru III III II O/Ru -OH and Ru -OH/Ru -OH2 processes (red lines in Figures S17 and S19), thus making the stability region of the Ru(III) species very small (∆E1/2 = 30 mV, Table 1). The decrease in the stability region of Ru(III) when introducing carbene ligands in Ru polylyridilic 8,15b which can be confirmed complexes has already been described, in our case if comparing with the ∆E1/2 value for 2+ [Ru(trpy)(bpy)(OH2)] (130 mV, Table 1). This tendency, however, 2+ 2+ can be reversed when replacing the trpy ligand in 2a and 2b by the facial aliphatic ligand bpea (Figure S22), since the higher σdonating and lower π-acceptor capacity of bpea provoke a 21 III/II stabilization of the Ru(III) state (lowering the E1/2 potential by IV/III 160-170 mV while keeping E1/2 unaltered, entries 1-2 and 4, 2+ Table 1). Consequently, ΔE1/2 is 200 mV for 6 . Unfortunately, for 2+ IV III the tpm derivative 4 the Ru -O/Ru -OH process could not be detected (Figure S21). The absence of the Ru(IV/III) redox couple in CV experiments is quite common for aqua complexes and is due to slow heterogeneous electron-transfer kinetics from the solution to 22 the electrode surface. Finally, the effect of the higher σ-donating character of the carbene ligand compared to bpy is evidenced when III/II 2+ 2+ comparing the E1/2 values of 4 and [Ru(tpm)(bpy)(OH2)] (cathodic shift of 50 mV, entries 3 and 6, Table 1). The simultaneous removal of protons and electrons (PCET processes) taking place for the four aqua-complexes can be observed in their Pourbaix diagrams (Fig. 8 and Figure S20), which III II have allows measuring their pKa1 (Ru -OH2) and pKa2 (Ru -OH2) 2+ 2+ values. Thus, the aqua groups of 6 (bpea) and 4 (tpm) for the Ru(III) state are more acidic than those corresponding to their meridional (trpy) counterparts (pka1 values of 1.2 and 1.8 vs 3.0-2.8, Table 1), while no significant differences are observed among the pKa2 values. Finally, higher acidities are observed for their noncarbene analogues (lower pka1 and specially pka2 values, entries 57, Table 1), given the lower σ-donating character of bpy compared to the carbene bidentate ligand. This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 7 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name S18d). In summary, from an electronic point of view all aqua complexes favour mono-electronic transfers between Ru(II), Ru(III) and Ru(IV). AQUI PODRIA SER XULO CALCULAR EL POTENCIAL iv/ii I ESPECULAR UNA MICA SOBRE LA TENDENCIA DEL iv D’ANAR + + DIRECTEAMENT A ii O A iii. However for 2a and 2b their tendency for IV/II reaction is very similar to the one electron transfer processes whereas in all the other cases the 1 electron transfer process is clearly favoured. The UV-vis spectra of the eight complexes described in this work have been recorded in methanol and are displayed in Figure S23 in the Supporting Information. Two regions can be observed in all cases: one region between 260 nm and 350 nm (or 325 nm for + 2+ 5 /6 ) with very intense bands due to intra ligand π-π* transitions, + 2+ and a second one between 350 nm (or 325 nm for 5 /6 ) and 550 nm, where typical broad unsymmetrical metal-to-ligand charge transfer (MLCT) bands appear, which could be tentatively assigned 19,21 to Ru(dπ)-N ligand(π*) transitions. Also, the electronic nature of the monodentate ligand influences to some extent the energies of the transitions involving Ru d orbitals. Thus, the MLCT bands for the Ru-aqua complexes are blue-shifted with regards to those of their Ru-Cl counterparts due to the relative stabilization of the Ru(dπ) levels provoked by the non-π-donor character of the aqua ligand. 2+ Figure 8. Plot of E1/2 vs pH (Pourbaix diagram) for complexes 2a2+ (a), 42+ (b) and 62+ (c). The pH/potential regions of stability for the various oxidation states and their dominant proton compositions are indicated by using abbreviations such as RuII-OH2, for example, for [RuII(L2)(OH2)(T)]2+ (T = trpy, tpm, bpea). The vertical lines in the various E/pH regions show the pKa values. Also, in order to confirm the correspondence of all observed redox waves to mono-electronic electrochemical processes, bulk electrolysis experiments were carried out at pH 4.9 for the aqua 2+ complexes (Figure S18 in the Supporting Information). Thus, for 2a at 0.75 V vs SCE (just after the predicted potential of the second redox wave) a value of 2.06 electrons per complex molecule was 2+ obtained (Figure S18a), while for 4 at 0.6 V (after the potential of the unique redox wave observed) a value of 0.97 electrons per molecule was obtained (Figure S18b). Finally, the stability of the III Ru -OH species and the stepwise mono-electronic nature of both III/II IV/III 2+ Ru and Ru processes have been confirmed for 6 , since after applying a potential of 0.57 V vs SCE (just after the expected potential of the first redox process), a value of 0.91 electrons per molecule was obtained (Figure S18c), while when the potential was set at 0.75 V, 1.87 electrons were transferred per molecule (Figure Electrochemical and chemical water oxidation by complexes 2a , 2+ 2+ 2+ 2b , 4 and 6 . The capacity of the aqua complexes to oxidize water into dioxygen was initially tested electrochemically. For this 2+ 2+ 2+ purpose, the CVs of 2a , 4 and 6 were recorded in aqueous solution at pH 1.0 until redox potentials were high enough to reach the oxidation states potentially able to oxidize water. Accordingly, a large electrocatalytic wave above 1.4 V vs SCE corresponding to the oxidation of water to dioxygen was observed in all cases (see below). In order to obtain kinetic information about the catalytic 23 process, a “foot of the wave analysis” (FOWA) was carried out to calculate the apparent rate constant kobs. For that purpose we followed the equations adapted for water oxidation recently 24 reported. Thus, under catalytic conditions, equation 1 is operative: B = . # ?L Ӛ * 2 * Ә 2 EA:E әӛ (1) 0 where E PQ is the standard potential for the catalysis-initiating redox V IV couple (which corresponds to the pH independent Ru O/Ru O 2+ 2+ wave, observed at 1.29 V for 2a , at 1.33 V for 4 and at 1.28 V for 2+ 6 according to the DPVs shown in Figure S26 in the Supporting Information and shown in Table 1), i is the CV current intensity in 0 the presence of substrate, i p is the peak current intensity of a oneelectron redox process of the catalyst (we approximate this current III II to the current associated with the Ru /Ru couple), F is the Faradaic -1 -1 constant, ν is the scan rate and R is 8.314 J·mol ·K , thus allowing the extraction of kobs. As an example, Fig. 9 shows the CV of a 0.69 2+ 0 mM solution of 4 at pH 1.0 (Fig. 9a) and the plot of i/i p vs + 0 1/{1 exp[(F/RT)(E PQ-E)]} (Fig. 9b) as well as the dependence of kobs on catalyst concentration (Fig. 9b, inset). Identical studies have 8 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE 2+ 2+ been performed for 2a and 6 , which can be found in Figure S25 in the Supporting Information. Figure 9. Background corrected CV of a 0.68 mM solution of 42+ in aqueous triflic acid 0.1 M (pH 1.0) at 100 mV/s scan rate (a), and “foot of the wave analysis” of 42+ by plotting i/i0p vs 1/{1+exp[(F/RT)(E0PQ-E)]} (b). Inset: plot of the different kobs values extracted from the “foot of the wave analysis” at each concentration (the dotted line represents the trend of the kobs values). In all cases, the largest slope at the very beginning of the catalytic process (which translates to the foot of the wave in the original CVs) gives the value of kobs, which is independent of catalyst concentration, probably indicating the existence of a water 25 nucleophilic attack (WNA) mechanism. Moreover, under the used electrocatalytic scheme, kobs is equivalent to the maximum turnover frequency (TOFmax) that a catalyst molecule can operate the water 23 oxidation reaction when the applied potential tends to infinite. At -1 pH 1.0, the obtained kobs values (expressed in s ) follow the trend 2+ 2+ 2+ 2a (0.570) > 6 (0.051) > 4 (0.015). Finally, the relationship between the turnover frequency TOF and the overpotential (η), defined as the difference between the applied potential E and the thermodynamic potential of the 0 catalysed reaction E AC, in this case water oxidation, is governed by equation 2, whose logarithms for all three aqua compounds at pH 1.0 are plotted in Figure 10 (catalytic Taffel plots). TOF = # ?L Ӛ EA:E * ( 2 η)ӛ (2) Figure 10. Catalytic Taffel plots for 2a2+ (green), 42+ (red) and 62+ (blue) at pH 1.0. 0 2+ Fig. 10 shows how the higher value of E PQ for 4 (1.33 V, Table 1) translates in lower turnover frequencies when η is low (red line before reaching the plateau, when η makes TOF reach its maximum and equals kobs). Also, it is made evident the higher performance of 2+ 2a (green line), in concordance with the higher kobs values deduced by the “foot of the wave analysis”. However, it should be noted that the kinetic parameters for catalytic reactions derived from electrochemical measurements depend on various details of the experimental procedures, and therefore values from different 26 studies should be compared carefully. The four aqua complexes were also tested as chemically triggered water oxidation catalysts in the presence of Ce(IV) as sacrificial oxidant. The total gas evolved was manometrically measured (Figure S27 in the Supporting Information) and its composition in terms of O2:CO2 ratio was analyzed by means of online Mass Spectrometry (Figure S28). In the presence of 100 2+ equivalents of Ce(IV) at pH 1, 4 generated more gas (≈ 15 mBar) after 30 min of reaction than the other three complexes (Figure S28). In general, and only considering the amount of generated gas, facial complexes are superior to their meridional counterparts. However, when the composition of the generated gases is analyzed 2+ by on-line MS (Figure S28), 4 has the lowest O2:CO2 ratio (1:5.5), 2+ followed by 6 , with a 1:1.4 ratio, since the O2:CO2 ratio was much 2+ 2+ higher for 2a and 2b (1:0.6). Therefore, despite still poor, the 2+ 2+ stability of the meridional trpy-based complexes 2a /2b is clearly 2+ 2+ higher than that of their facial (tpm or bpea) counterparts 4 /6 , that easily get oxidized in the harsh reaction conditions of chemical water oxidation by Ce(IV) at pH = 1.0. This is clearly reflected in Figure S29, where the profile of O2 evolution of the four aqua complexes has been compared. Therefore, if taking into account the volume of the vial (16.04 mL) and the amount of catalyst used (2.0 2+ 2+ μmol), the turnover numbers (TN) at 298K for 2b and 2a (2.39 2+ 2+ and 2.17, respectively) are higher than those of 6 (1.63) and 4 (0.75). Moreover, this behaviour is consistent with the results obtained during the electrochemically triggered water oxidation at pH 1.0, with the highest TOF value corresponding to the trpy 2+ 2+ 2+ derivatives (2a /2b ) and the lowest one to the tpm complex (4 ). Catalyst-catalyst intermolecular oxidative degradation involving IV 27 Ru =O species or the direct degradation of the complexes by the highly oxidant Ce(IV) species are considered as the potential origin of the evolved CO2. In our system, the only relevant differences between the four evaluated complexes are the tridentate ligands employed. Therefore, tpm and bpea (both containing aliphatic carbon atoms prone to be easily oxidized in the harsh catalytic conditions employed) quickly decompose generating large amounts of CO2 that arise from ligand oxidation. Given that a great number of robust water oxidation catalysts containing the trpy ligand have Error! Bookmark not defined.,28 been reported, the observed evolution of CO2 2+ 2+ from 2a /2b clearly reflects a relative weakness of the PhthaPzOR family of ligands under oxidative conditions. Electrochemical and chemical alkene epoxidation by complexes 2+ 2+ 2+ 2+ 2+ 2+ 2a , 2b , 4 and 6 . The capacity of the aqua complexes 2a , 4 2+ and 6 to electrocatalytically epoxide cis-β-methylstyrene has been investigated by CV. All experiments were performed in DCM under well-controlled concentrations of catalyst and substrate, whose concentration was steadily increased. In all cases, the presence of This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 9 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name the alkene provoked significant electrocatalytic currents due to its oxidation from 1.2 V vs Hg/Hg2SO4 onwards (see Figures S30, S33 and S36 in the Supporting Information). The rate constant value k for the electrocatalytic epoxidation reaction can be estimated from the plot of Icat vs the square root of 29 substrate concentration according to equation 3: 1/2 1/2 1/2 Icat = nFA[cat]D k [subs] (3) where Icat is the current intensity in the presence of cis-βmethylstyrene, n is the number of electrons involved in the catalysis, F is the Faraday constant, A is the surface area of the 2 2 working electrode in cm (0.07 cm in our case), [cat] is the concentration of catalyst in mM, D is the diffusion coefficient of the 2 catalyst in cm /s and [subs] is the concentration of cis-βmethylstyrene in mM. 1/2 The plot of Icat vs [subs] shows a linear trend with the increasing concentration of substrate and, under kinetic control 1/2 conditions, the slope is proportional to k (see Figures S31, S34 and S37 in the Supporting Information). In order to estimate the value of the rate constant, the diffusion coefficient D was calculated from the peak current prior the addition of the substrate according 29 to equation 4: 5 3/2 1/2 1/2 Ip = 2.69·10 n AD [cat]ν (4) where Ip is the current intensity at 1.6 V vs Hg/Hg2SO4, n is the number of electrons involved in the electrochemical process, A is 2 the surface area of the working electrode in cm , D is the diffusion 2 coefficient of the catalyst in cm /s, [cat] is the concentration of catalyst in mM and ν is the scan rate in V/s. If a linear relationship 1/2 1/2 for Ip vs ν is obtained, the slope is proportional to AD . As shown in Figures S32, S35 and S38 in the Supporting Information, the plot 1/2 of Ip vs ν presents a good linear trend for the 20 - 200 mV/s range, and consequently the D values have been obtained, varying -4 2+ -4 2 2+ 2+ from 1.1·10 (6 ) to 2.0·10 cm /s (2a and 4 ). From the combination of equations 3 and 4 the rate constants (k) of the three tested aqua complexes were calculated. Contrarily to what was observed when employing this set of catalysts in the chemical oxidation of water at pH 1.0 (where the decomposition of 2+ 2+ 2+ both the facial complexes 4 and 6 was extremely fast), now 6 is by far the most efficient electro-catalyst for the epoxidation of cis-1 -1 2+ β-methylstyrene in DCM (k = 961 M ·cm for 6 compared to 576 -1 -1 2+ 2+ and 441 M ·cm for 2a and 4 , respectively). The different oxidation states involved in Ru mononuclear complexes (Ru(IV) for the epoxidation of a double bond and Ru(V) for the oxidation of water) may be the reason for the different relative efficiency in these two oxidative transformations of the set of aqua complexes here studied. 2+ 2+ 2+ Complexes 2a , 4 and 6 have also been tested with regards to their ability to chemically oxidize alkenes. The catalytic reactions have been carried out using a catalyst:substrate:oxidant:water ratio of 1:1000:2000:2000 after a 120 min mixing period of the catalysts in the absence of substrate (see Experimental Section for further details), during which the excess of water ensures the generation of 12,30 the oxidant PhIO species from PhI(OAc)2. This mixing period before substrate addition is crucial in order to improve the rate of the catalytic reaction. Scheme S2 summarizes the set of reactions that take place during the catalytic epoxidation of alkenes for the proposed systems. All products of each catalytic experiment have been identified by GC-MS, and all gathered results are shown in 2+ Table 2. For instance, the system: 2a 1.7 mM, cis-β-methylstyrene 1.7 M, PhI(OAc)2 3.4 M, H2O 3.4 M in DCE (entry 2) gives 1.42 M of cis-β-methylstyrene oxide in 525 minutes, which represents a TN -1 value of 840 and a TOF value of 1.6 min , and since the conversion of the initial substrate is complete the selectivity in the epoxide formation is 84%. Table 2. Catalytic performance of 2a2+ to 62+ in the epoxidation of cis- and trans-alkenes using PhIO as oxidant in DCE.a Cat. Entry Alkene Conv. (%)b Selec. (%)c TN/TOFd 2a2+ 1 styrene 42 46 194/0.8 e 2 >99 84 trans-stilbenef >99 68 680/1.3 4 2+ cis-β-methylstyrene 3 840/1.6 cyclooctene >99 93 930/1.9 styrene 29 66 191/1.1 cis-β-methylstyrene >99 82e 816/1.3 7 trans-stilbenef >99 60 596/1.1 8 2+ 5 6 2b cyclooctene 99 96 946/2.2 9 23 26 60/0.5 cis-β-methylstyrene 97 56e 545/0.4 11 trans-stilbenef 90 16 148/0.3 12 62+ styrene 10 4 cyclooctene >99 76 756/0.3 13 styrene 21 13 27/0.1 e 14 cis-β-methylstyrene 99 69 15 trans-stilbenef 91 15 687/0.7 136/0.2 16 cyclooctene >99 94 940/0.4 a Catalyst:substrate:oxidant:water ratio of 1:1000:2000:2000. See Experimental Section for further details. b Substrate conversion = {[substrate]initial - [substrate]final}/[substrate]initial·100. c Epoxide selectivity = [epoxide]final/{[substrate]initial-[substrate]final}·100. d TN is the turnover number with regard to the total epoxide obtained. TOF is the turnover frequency expressed in epoxide cycles per minute (TN/min). e cis epoxide. f DCE volume is 5 mL. Similar figures are obtained for both trpy-based aqua2+ 2+ complexes (2a /2b ) on the one hand and for both facial 2+ 2+ derivatives (4 /6 ) on the other. Also, when comparing both sets of catalyst pairs, a clearly higher epoxidation capacity (higher 2+ 2+ conversion and selectivity) is observed for 2a /2b compared to 2+ 2+ 2+ 4 /6 . For example, for styrene 2a yields a 42% conversion (entry 2+ 2+ 1), while 4 and 6 only reach 23 and 21% conversion, respectively 2+ (entries 9 and 13), and selectivity for 2b is 66% (entry 5) while it is 2+ 2+ only 26% and 13% for 4 and 6 , respectively. Also, for cis-β2+ methylstyrene selectivities above 80% are obtained for 2a and 2+ 2+ 2+ 2b (entries 2 and 6), while for 4 and 6 they are below 60% and 70%, respectively (entries 10 and 14), and for trans-stilbene complete conversion and selectivities above 60% are obtained for 2+ 2+ 2+ 2+ 2a and 2b (entries 3 and 7), while for 4 and 6 conversion is around 90% and selectivity near 15% (entries 11 and 15). This behaviour can be rationalized on the basis of the electronic nature 2+ 2+ of the two pairs of complexes. Thus, while for 2a /2b bielectronic transfers between the Ru(II) and Ru(IV) species are thermodynamically almost as favourable as the mono-electronic 10 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE processes (Ru(III) stability region is minimal with regards to its 2+ 2+ disproportionation, Fig. 8a and S20), for 4 /6 clearly monoelectronic processes take place (Fig. 8b-c). It is well known that catalysts favouring bi-electronic processes drive epoxidation reactions to concerted pathways and mono-electronic ones drive them to radical mechanisms, the latters usually ending up reducing the selectivity of the whole process by the generation of a wide set 8,15b, 31 of by-products (Scheme S3). Therefore, the existence of bi2+ 2+ electronic processes for 2a /2b could explain the higher selectivity observed with regards to their mono-electronic 2+ 2+ counterparts 4 and 6 . Also, together with these electronic arguments, other conceivable reasons for the reduced epoxidation 2+ 2+ capacity of 4 /6 may arise from the chemical nature of their facial ligands, since tpm and bpea are prone to be oxidized under oxidative conditions (they posses aliphatic C atoms), and their steric bulkiness may also difficult the interaction between the substrates and the catalyst active site. Interestingly, different results have been obtained with related Ru-N5C complexes containing the same auxiliary trpy or bpea ligands but the smaller NHC ligand N-methylN’-2-pyridylimidazolium, where the bpea-containing complex yields higher selectivity in front of styrene and higher conversion efficiency and selectivity towards trans-stilbene than its 15b corresponding trpy-complex. Therefore, these results demonstrate again the dramatic influence of the electronic and steric properties of the carbene ligand on the catalytic performance of the Ru complexes. Table 2 also shows that the studied aqua complexes perform much better with substrates containing electron-donor groups than with those bearing electron-withdrawing substituents, indicating IV the strong electrophilic character of the Ru =O group in all cases. Therefore, the best results are gathered for cyclooctene (entries 4, 8, 12 and 16) whereas the poorest values are obtained for styrene (entries 1, 5, 9 and 13) and trans-stilbene (entries 3, 7, 11 and 15), the latter also suffering from potential steric effects due to the bulkiness of its two phenyl rings. Finally, another interesting feature observed is the stereospecific nature of the catalytic epoxidation process. For the whole set of aqua complexes when cis-β-methylstyrene is employed as substrate no cis/trans isomerization takes place. Therefore, for 2+ 2+ 4 /6 ring closure must be faster than C-C rotation for the radical intermediates proposed to be formed (Scheme S3, top), while for 2+ 2+ 2a /2b the stereospecificity could be explained on the basis of the proposed concerted bi-electronic oxene insertion to the double bond (Scheme S3, bottom). Conclusions A new tetradentate NHC ligand has been synthesized and fully characterized by NMR and X-ray diffraction analysis. This ligand decomposes in nucleophilic solvents at high temperatures due to CN bond cleavage, generating a bidentate NHC-phtalazine scaffold (PhthaPz-R) during the synthesis of the corresponding four Ru n+ chloro and aqua complexes [Ru(PhthaPz-R)(T)X] (X = Cl, n = 1, X = H2O, n = 2 ; R = Me, iPr; T = trpy, tpm, bpea), which have been fully characterized electronically and spectroscopically. Modulation of the thermodynamic stability in aqueous media of the Ru(III) oxidation state has been observed for the four aqua 2+ 2+ compounds. Thus, while for 4 /6 (T = tpm/bpea) the Ru(III) state is clearly stable at moderately high potentials and they increase their oxidation state from Ru(II) through mono-electronic processes (ΔE1/2 = 200 mV for the latter), for the trpy-based complexes 2+ 2+ 2a /2b the Ru(III) state is almost unstable with regards to its disproportion (ΔE1/2 = 30 mV). This divergence in the electronic behaviour has direct implications in the epoxidation capacity of alkenes with PhI(OAc)2, since the higher conversion and selectivity 2+ 2+ observed for 2a /2b can be rationalized on the basis of the existence of bi-electronic transfers that avoid the generation of radical intermediates of high energy that could reduce the selectivity of the whole process. Additionally, the absence of cis/trans isomerization in all cases -therefore leading to stereospecific epoxidation processes- may be explained on the basis 2+ 2+ of either a concerted bi-electronic process (2a /2b ) or a radical mechanism in which the ring closure is much faster than C-C 2+ 2+ 2+ rotation (4 /6 ). Finally, 6 is by far the most efficient electrocatalyst for the epoxidation of cis-β-methylstyrene. We have also shown that the four aqua complexes are moderately unstable during catalytic water oxidation triggered by Ce(IV) addition due to ligand oxidation under the harsh conditions employed, especially those containing aliphatic carbon atoms 2+ 2+ 2+ (4 /6 ). Also, under electrochemically triggered conditions 2a is the fastest catalyst at pH 1.0. In conclusion, in this work we have evidenced that it is possible to modulate the electronic and catalytic properties of Ru NHC complexes by using different auxiliary meridional or facial Ntridentate ligands. Experimental section Materials and instrumentation. All reagents used in the present work were obtained from Sigma Aldrich Chemical Co. and were used without further purification. Reagent-grade organic solvents were obtained from Scharlab. RuCl3·3H2O was supplied by Alfa Aesar. The starting ligands tri(1H-pyrazol-1-yl)methane (tpm) and N,N-bis(pyridin-2-ylmethyl)ethanamine (bpea) were prepared as 32,33 described in the literature. The synthetic manipulations were routinely performed under nitrogen atmosphere using Schlenk flask and vacuum-line techniques. UV-vis spectroscopy was carried out by a HP8453 spectrometer using 1 cm quartz cells. NMR spectroscopy was performed on a Bruker DPX 250 MHz, DPX 360 MHz, DPX 400 MHz, DPX 500 MHz or a DPX 600 MHz spectrometer. Samples were run in MeOD, DCM-d2 or acetone-d6 with internal references. Elemental analyses were performed using a Carlo Erba CHMS EA-1108 instrument from the Chemical Analysis Service of the Universitat Autònoma de Barcelona (SAQ-UAB). Electrospray ionization Mass Spectrometry (ESI-MS) experiments were performed on a HP298s gas chromatography (GC-MS) system from the SAQ-UAB. Cyclic voltammetry and differential pulse voltammetry experiments were performed on the Bio Logic Science Instrument SP-150 potentiostat using a three-electrode cell. A glassy carbon electrode (7 mm diameter) was employed as the working electrode while platinum wire as the auxiliary electrode and a SCE as the reference electrode. This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 11 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name Working electrodes were polished with 0.05 micron Alumina paste and washed with distilled water and acetone before each measurement. The complexes were dissolved in acetonitrile, methanol or dichloromethane solutions of 0.1 M ionic strength containing the necessary amount of n-Bu4NPF6 (TABH) as supporting electrolyte. For the electrochemical analysis performed in water, the complexes were dissolved in pH 1 triflic acid solution or solutions of phosphate buffer for other pHs, with a 0.1 M ionic strength. The pH values were increased or reduced by adding drops of a 0.1 M NaOH solution or the pH 1 triflic acid solution. E1/2 values here presented were estimated from CV experiments from the + average of the oxidative and reductive peak potentials (Ep,a Ep,c)/2. The electrocatalysis of alkene epoxidation was carried out in dichloromethane (0.1M TBAPF6) at increasing concentrations of cisβ-methylstyrene with a glassy carbon as the working electrode and Hg/Hg2SO4 as the reference electrode. The CVs were recorded at a scan rate of 100 mV/s. For the epoxidation catalytic studies, experiments were performed as follows. First, a mixing period of 120 min was carried out by adding in a vial 1 mL of 1,2dichloroethane (DCE) as solvent, 1.60 g (5.0 mmol) of (diacetoxyiodo)benzene (PhI(OAc)2) as oxidant, 1 mmol of 1,1’-3 2+ 2+ biphenyl as internal standard, 2.5·10 mmol of catalyst (2a to 6 ) and 90 µL (5.0 mmol) of water. This mixing period before substrate addition was observed to be key in order to improve the rate of the catalytic reaction. Then, the substrate (2.5 mmol) was added to the previous mixture, achieving a final volume of approx. 1.47 mL and the corresponding initial concentrations: catalyst, 1.7 mM; substrate, 1.7 M; biphenyl, 0.68 M; PhI(OAc)2, 3.4 M; water, 3.4 M. These concentrations correspond to a catalyst:substrate:oxidant:water ratio of 1:1000:2000:2000. Aliquots were taken every 5, 10, 15, 20, 25 or 30 min until completion of reaction. Each aliquot was filtered through a Pasteur pipette filled with celite; after that diethyl ether was added in order to elute the organic compounds and the filtrate was analyzed in an HP 5890 PACKARD SERIES II Gas Chromatograph (GC) coupled to a mass selective detector with ionization by electronic impact. The characterization of the reaction products was done by comparison with commercial products or by GC-MS spectrometry. GC conditions: initial temperature 40 °C for 10 min, ramp rate variable for each substrate (typically from 10 °C/min to 20 °/min), final temperature 250 °C, injection temperature 220 °C, detector temperature 250 °C. Yield of epoxide and substrate conversion were calculated with regard to the initial concentration of substrate. Substrate conversion = {[substrate]initial [substrate]final}/[substrate]initial·100. Epoxide selectivity = [epoxide]final/{[substrate]initial-[substrate]final}·100. On-line manometry measurements were performed on a Testo 521 differential pressure manometer with an operating range of 1 to 100 hPa and a measurement accuracy of 0.5%, coupled to thermostatted reaction vessels for dynamic monitoring of the headspace pressure above each reaction. On-line monitoring of the gas evolution was carried out on a Pfeiffer Omnistar GSD 301C mass spectrometer. Typically, a degassed vial of 16.04 mL containing 1.5 mL of a 1.33 mM solution of the catalysts in 0.1 M triflic acid was connected to the apparatus capillary tubing. Subsequently, 0.5 mL IV of an Ar degassed solution of (NH4)2Ce (NO3)6 400 mM in 0.1 M triflic acid (100 equiv.) were injected by a Hamilton gastight syringe, and the reaction was dynamically monitored at 25 °C. A response ratio of 1:2 was observed when equal concentrations of dioxygen and carbon dioxide were injected, which was used for the calculation of their relative concentrations. 2+ X-ray Crystal Structure Determination. Crystals of L1 were grown by slow diffusion of diethyl ether into a solution of L1(PF6)2 in + acetone. Crystals of 5 were prepared by slow diffusion of diethyl + ether into a solution of 5 in methanol. Structure solution and refinement was performed using 2+ + SHELXTL . The crystal data parameters of L1 and 5 are listed in 2+ + Table S1 and S2. The structures of L1 and 5 were analyzed using the programs ORTEP and Mercury. Synthetic Preparations. 1,4-bis(1-methylimidazolium-1-yl)phthalazine dichloride (L1(Cl)2): To an evacuated Schlenk flask a mixture of 1,4-dichlorophthalazine (dcp) (990 mg, 0.5 mol) and 1-methylimidazole (2.050 g 3 mol) were dissolved into 2 ml of DMF. The mixture was stirred under a nitrogen atmosphere at 120°C for 4 hours. A white precipitate appeared in the reaction crude, which was filtered off, washed with DMF and diethyl ether and dried under vacuum. Yield: 1.26 g (70%). 1 H-NMR (600 MHz, acetone-d6, 298K) δ=9.95 (s, 2H, H6, H6’), 8.57 (dd, 2H, J9-10 = 6.2, 3.0 Hz, H9, H9’), 8.50 (s, 2H, H4, H4’), 8.46 (dd, 2H, J10-9 = 6.3, 3.0 Hz, H10, H10’), 8.23 (s, 2H, H3, H3’), 4.39 (m, 6H, 13 H1). C-NMR (151 MHz, acetone-d6, 298K) δ=150.65 (C7), 138.44 (C6), 136.50 (C10), 125.28 (C3), 124.16 (C9), 124.08 (C8), 123.57 (C4), 36.84 (C1). Elemental analysis (% found): C, 52.98; H, 4.49; N, 23.09. Calcd for C16H16Cl2N6: C, 52.90; H, 4.44; N, 23.14. II cis-[Ru (PhthaPz-OMe)(trpy)Cl]PF6 (1a(PF6)): [Ru(trpy)Cl3] (130 mg, 0.3 mmol), 1,4-bis(1-methylimidazolium-1-yl)phthalazine dichloride (L1(Cl)2) (73 mg, 0.2 mmol) and LiCl (38 mg 0.9 mmol) were mixed in a round bottom flask and dry methanol (20 mL) was added as solvent. Triethylamine (121 mg, 166 μL, 1.2 mmol) was added to the solution and the mixture was refluxed at 65°C for 16 hours. After cooling to room temperature, the reaction crude was filtered ® through celite to remove the black solid formed and then 20 drops of saturated NH4PF6 aqueous solution were added to the filtrate. The solution was concentrated under vacuum until about 10 mL, when a brown precipitate appeared. The precipitate was filtered off, washed with diethyl ether and dried under vacuum. Yield: 62 1 mg (41%). H-NMR (600 MHz, CD2Cl2, 298K) δ=8.63 (d, 1H, J4-3 = 2.4 Hz, H4), 8.53 (d, 1H, J9-10 = 8.7 Hz, H9), 8.37 (d, 2H, J26-27 = 8.1 Hz, H26), 8.22 (d, 2H, J23-22 = 8.0 Hz, H23), 8.18 (t, 1H, J27-26,26’ = 8.1 Hz, H27), 8.12 (d, 1H, J12-11 = 8.1 Hz, H12), 8.07 (td, 1H, J10-9,11 = 7.8 Hz, J10-12 = 1.1 Hz, H10), 7.94 (d, 2H, J20-21 = 5.3 Hz, H20), 7.85 (t, 1H, J1110,12 = 7.6 Hz, H11), 7.82 (t, 2H J22-21,23 = 7.8 Hz, H22), 7.69 (d, 1H J3-4 = 2.4 Hz, H3), 7.20 (td, 2H , J21-20,22 = 6.5 Hz, J21-23 = 1.1 Hz, H21), 13 4.78 (s, 3H, H1), 3.47 (s, 3H, H18). C-NMR (151 MHz, CD2Cl2, 298K) 200.66 (C6), 158.75 (C24), 158.43 (C14), 156.51 (C20), 155.50 (C25), 12 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE 151.45 (C7), 136.59 (C22), 135.43 (C27), 133.91 (C10), 132.29 (C11), 126.88 (C21), 125.83 (C3), 124.51 (C12), 122.95 (C23), 121.16 (C26), 121.00 (C8), 120.20 (C9), 119.51 (C13), 118.77 (C4), 54.61 (C18), -1 -1 38.15 (C1). UV/vis (methanol): λmax, nm (ε, M ·cm )= 281 (11988), 313 (14247), 413 (4700), 475 (4332). ESI-MS (MeOH): m/z = 610.1 ([M-PF6-1]). Elemental analysis (% found): C, 44.58; H, 3.10; N, 12.95. Calcd for C28H23ClF6N7OPRu: C, 44.54; H, 3.07; N, 12.99. II cis-[Ru (PhthaPz-OiPr)(trpy)Cl]PF6 (1b(PF6)): [Ru(trpy)Cl3] (130 mg, 0.3 mmol), 1,4-bis(1-methylimidazolium-1-yl)phthalazine dichloride (L1(Cl)2) (73 mg, 0.2 mmol) and LiCl (38 mg 0.9 mmol) were mixed in a round bottom flask and dry isopropanol (20 mL) was added as solvent. Triethylamine (121 mg, 166 μL, 1.2 mmol) was added to the solution and the mixture was refluxed at 83°C for 16 hours. After cooling to room temperature, the reaction crude was filtered ® through celite to remove the black solid formed and 20 drops of saturated aqueous NH4PF6 were added to the filtrate. The solvent was then totally removed in a rotary evaporator and the brown solid obtained was redissolved in isopropanol. The mixture was ® filtered through celite and isopropanol was removed from the filtrate under vacuum until about 10 mL left. During this process a brown precipitate appeared, which was filtered off, washed with 1 diethyl ether and dried under vacuum. Yield: 55 mg (35%). H-NMR (600 MHz, acetone-d6, 298K) δ=9.02 (d, 1H J4-3 = 2.4 Hz, H4), 8.84 (d, 1H, J9-10 = 9.0 Hz, H9), 8.75 (d, 2H, J27-28 = 8.1 Hz, H27), 8.57 (d, 2H, J24-23 = 15.8 Hz, H24), 8.35 (t, 1H, J28-27,27’ = 8.1 Hz, H28), 8.11 (m, 4H, J21-22 = 7.2 Hz, H21; J12-11 = 4.8 Hz, H12; J10-9,11 = 9.0 Hz, H10), 8.00 (d, 1H, J3-4 = 2.4 Hz, H3), 7.92 (m, 3H, H11, H23), 7.29 (ddd, 1H, J2221,23,24 = 7.0, 5.6, 1.2 Hz, H22), 4.79 (s, 3H, H1), 4.54 (sept, 1H, J18-19 = 13 6.2 Hz, H18), 1.09 (d, 1H, J19-18 = 6.2 Hz, H19). C-NMR (151 MHz, acetone-d6, 298K) 200.91 (C6), 159.08 (C25), 157.41 (C14), 156.82 (C21), 155.61 (C26), 151.44 (C7), 136.70 (C23), 135.48 (C28), 133.82 (C10), 132.09 (C11), 126.85 (C22), 126.03 (C3), 124.30 (C12), 123.13 (C24), 121.64 (C27), 121.28 (C8), 120.94 (C9), 119.61 (C13), 119.14 (C4), 70.79 (C18), 37.48 (C1), 20.96 (C19). UV/vis (methanol): λmax, -1 -1 nm (ε, M ·cm )= 276 (11315), 314 (14616), 413 (5036), 479 (3889). ESI-MS (MeOH): m/z = 638.1 ([M-PF6-1]). Elemental analysis (% found): C, 46.07; H, 3.52; N, 12.49. Calcd for C30H27ClF6N7OPRu: C, 46.01; H, 3.48; N, 12.52. II [Ru (PhthaPz-OMe)(tpm)Cl]PF6 (3(PF6)): [Ru(tpm)Cl3] (130 mg, 0.3 mmol), 1,4-bis (1-methylimidazolium-1-yl)phthalazine dichloride (L1(Cl)2) (73 mg, 0.2 mmol) and LiCl (38 mg 0.9 mmol) were mixed in a round bottom flask and dry methanol (20 mL) was added as solvent. Triethylamine (121 mg, 166 μL, 1.2 mmol) was added to the solution and the mixture was refluxed at 65°C for 16 hours. After cooling to room temperature, the reaction crude was filtered ® through celite to remove the black solid formed and 20 drops of saturated aqueous NH4PF6 were added to the filtrate. The methanolic solution was concentrated in a rotary evaporator until about 10 mL and a brown precipitate was obtained. The precipitate was filtered off, washed with diethyl ether and dried under vacuum. 1 Yield: 88 mg (60%). H-NMR (600 MHz, acetone-d6, 298K) δ=9.66 (s, 1H, H24), 8.88 (d, 1H, J4-3 = 2.3 Hz, H4), 8.87 (d, 1H, J9-10 = 8.6 Hz, H9), 8.68 (d, 1H, J20-21 = 1.6 Hz, H20), 8.57 (d, 1H, J31-32 = 2.3 Hz, H31), 8.52 (d, 1H, J22-21 = 2.2 Hz, H22), 8.47 (d, 1H, J33-32 = 1.7 Hz, H33), 8.46 (d, 1H, J26-27 = 2.5 Hz, H26), 8.39 (d, 1H, J12-11 = 8.0 Hz, H12), 8.20 (t, 1H, J10-9,11 = 7.3 Hz, H10), 8.07 (t, 1H, J11-10,12 = 7.6 Hz, H11), 7.64 (d, 1H, J3-4 = 2.3 Hz, H3), 6.89 (d, 1H, J28-27 = 1.9 Hz, H28), 6.74 (t, 1H, J21-20,22 = 2.3 Hz, H21), 6.67 (t, 1H, J32-31,33 = 2.4 Hz, H32), 6.33 (t, 1H, J27-26,28 = 2.4 Hz, H27), 4.16 (s, 3H, H18), 3.73 (s, 3H, H1). 13 C-NMR (151 MHz, acetone-d6, 298K) 205.44 (C6), 157.87 (C14), 151.40 (C7), 149.12 (C33), 146.71 (C28), 146.66 (C20), 134.70 (C26), 133.97 (C31), 133.75 (C10), 132.43 (C22), 132.27 (C11), 124.89 (C3), 124.34 (C12), 121.57 (C8), 121.28 (C9), 120.17 (C13), 119.63 (C4), 108.41 (C32), 108.27 (C27), 107.51 (C21), 76.77 (C24), 55.04 (C18), -1 -1 36.27 (C1). UV/vis (methanol): λmax, nm (ε, M ·cm )= 302 (7799), 410 (4745). ESI-MS (MeOH): m/z = 591.1 ([M-PF6-1]). Elemental analysis (% found): C, 37.60; H, 3.05; N, 18.99. Calcd for C23H22ClF6N10OPRu: C, 37.53; H, 3.01; N, 19.03. II trans,fac-[Ru (PhthaPz-OMe)(bpea)Cl]PF6 (5(PF6)): [Ru(bpea)Cl3] (130 mg, 0.3 mmol), 1,4-bis(1-methylimidazolium-1-yl)phthalazine dichloride (L1(Cl)2) (73 mg, 0.2 mmol) and LiCl (38 mg 0.9 mmol) were mixed in a round bottom flask and dry methanol (20 mL) was added as solvent. Triethylamine (121 mg, 166 μL, 1.2 mmol) was added to the solution and the mixture was refluxed at 65°C for 16 hours. After cooling to room temperature, the reaction crude was ® filtered through celite to remove the black solid formed and 20 drops of saturated aqueous NH4PF6 were added to the filtrate. The methanolic solution was concentrated in a rotary evaporator until about 10 mL left and a brown precipitate appeared. The precipitate was filtered, washed with diethyl ether and dried under vacuum. 1 Yield: 68 mg (45%). H-NMR (600 MHz, acetone-d6, 298K) δ=9.63 (d, 1H, J20-21 = 5.3 Hz, H20), 9.56 (d, 1H, J34-33 = 5.0 Hz, H34), 8.84 (d, 1H, J4-3 = 2.0 Hz, H4), 8.79 (d, 1H, J9-10 = 8.3 Hz, H9), 8.25 (d, 1H, J12-11 = 8.0 Hz, H12), 8.12 (t, 1H, J10-9,11 = 7.5 Hz, H10), 7.97 (t, 1H, J11-10,12 = 7.6 Hz, H11), 7.92 (t, 1H, J32-31,33 = 7.3 Hz, H32), 7.82 (t, 1H, J22-21,23 = 7.4 Hz, H22), 7.58 (m, 2H, J3-4 = 2.3 Hz, J31-32 = 7.3 Hz, H3, H31), 7.50 (m, 1H, J23-22,33-32,34 = 7.3 Hz, H23, H33), 7.41 (t, 1H, J21-20,22 = 6.5 Hz, H21), 4.52-4.42 (m, 4H, H25, H29) 3.65 (s, 3H, H18), 3.58 (s, 3H, H1), 2.53 (m, 1H, J27-27’,28 = 13.8, 6.8 Hz, H27), 2.35 (m, 1H, J27’-27,28 = 13.7, 13 6.8 Hz, H27’), 0.91 (m, 3H, H28). C-NMR (151 MHz, acetone-d6, 298K) 204.97 (C6), 161.42 (C20), 160.02 (C34), 158.07 (C14), 151.65 (C24), 150.15 (C13), 149.42 (C30), 136.55 (C32), 125.73 (C22), 133.74 (C10), 131.47 (C11), 125.00 (C3), 124.30 (C12), 123.63 (C21), 123.13 (C33), 121.52 (C8), 121.01 (C23), 120.70 (C9), 120.64 (C31), 119.44 (C7), 118.85 (C4), 67.49 (C25), 66.09 (C29), 61.96 (C27), 53.89 (C18), 35.45 (C1), 7.98 (C28). UV/vis (methanol): λmax, nm (ε, -1 -1 M ·cm )= 299 (5226), 434 (5612). ESI-MS (MeOH): m/z = 604.1 ([M-PF6-1]). Elemental analysis (% found): C, 43.37; H, 3.94; N, 13.05. Calcd for C27H29ClF6N7OPRu: C, 43.29; H, 3.90; N, 13.09. II + cis-[Ru (PhthaPz-OMe)(trpy)(OH2)](PF6)2 (2a(PF6)2): 1a (120 mg, 0.16 mmol) was dissolved in a mixture of acetone and water (acetone: water = 1: 3, 40 mL). AgBF4 (109 mg, 0.56 mmol) was added into the solution, which was then refluxed at 90°C for 4 hours. After cooling to room temperature, the reaction crude was ® filtered through celite to remove the black solid formed. The redbrown solution was concentrated under vacuum until about 20 mL left, followed by centrifugation (10000rpm, 10min) to remove the potential colloidal silver still remaining. To the clear red solution 20 This journal is © The Royal Society of Chemistry 20xx J. Name., 2013, 00, 1-3 | 13 Please do not adjust margins Please do not adjust margins ARTICLE Journal Name drops of saturated aqueous NH4PF6 solution were added and the precipitate formed was filtered off, washed with diethylether and 1 dried under vacuum. Yield: 91 mg (65%). H-NMR (600 MHz, acetone-d6, 298K) 9.01 (d, 1H, J4-3 = 2.4 Hz, H4), 8.80 (d, 2H, J26-27 = 7.4 Hz, H26), 8.78 (d, J9-10 = 8.7 Hz, H9), 8.62 (d, 2H, J23-22 = 8.0 Hz, H23), 8.44 (t, 2H, J27-26,26’ = 8.1 Hz, H27), 8.19 (d, 2H, J20-21 = 5.0 Hz, H20), 8.12 (t, 1H, J10-9,11 = 8.7 Hz, H10), 8.04-8.00 (m, 4H, H12, H3, H22), 7.91 (t, 1H, J11-10,12 = 7.5 Hz, H11), 7.37 (m, 2H, H21), 4.56 (s, 13 3H, H1), 3.46 (s, 3H, H18). C-NMR (151 MHz, acetone-d6, 298K) 200.62 (C6), 159.47 (C24), 158.01 (C14), 157.82 (C20), 156.41 (C25), 153.08 (C7), 138.22 (C22), 137.65 (C27), 134.20 (C10), 132.83 (C11), 127.53 (C21), 126.29 (C3), 124.05 (C12), 123.85 (C23), 122.38 (C26), 121.12 (C9), 120.90 (C8), 119.57 (C14), 119.21 (C3), 54.43 (C18), -1 -1 36.55 (C1). UV/vis (methanol): λmax, nm (ε, M ·cm )= 275 (12189), 309 (13040), 388 (4338), 467 (4474). ESI-MS (MeOH): m/z = 594.1 ([M-2PF6]). Elemental analysis (% found): C, 38.14; H, 2.89; N, 11.06. Calcd for C28H25F12N7O2P2Ru: C, 38.11; H, 2.86; N, 11.11. II + cis-[Ru (PhthaPz-OiPr)(trpy)(OH2)](PF6)2 (2b(PF6)2): 1b (120mg, 0.15 mmol) was dissolved in a 40 mL mixture of acetone and water (1:3). AgBF4 (109 mg, 0.56 mmol) was then added to the solution, which was then refluxed at 90°C for 4 hours. After cooling to room ® temperature, the reaction crude was filtered through celite to remove the silver chloride formed. The brown filtrate was then concentrated in a rotary evaporator until about 20 mL, followed by centrifugation (10000 rpm, 10 min) to remove the remaining solids. To the clear red solution 20 drops of a saturated aqueous NH4PF6 solution were added. The brown precipitate formed was filtered off, washed with diethyl ether and dried under vacuum. Yield: 91 mg 1 (65%). H-NMR (600 MHz, acetone-d6, 298K) δ=9.03 (d, 1H, J4-3 = 2.4 Hz, H4), 8.84 (d, 2H, J27-28 = 6.7 Hz, H27), 8.81 (d, 1H, J9-10 = 8.7 Hz, H9), 8.63 (d, 2H, J24-23 = 8.0 Hz, H24), 8.50 (t, 1H, J28-27,27’ = 8.1 Hz, H28), 8.23 (dd, 2H, J21-22,23 = 10.5, 5.6 Hz, H21), 8.13 (t, 1H, J10-9,11 = 8.5, Hz, H10), 8.10 (d, 1H, J12-11 = 8.7 Hz, H12), 8.06-8.01 (m, 3H, H3, H23), 7.93 (t, 1H, J11-10,12 = 7.6 Hz, H11), 7.38 (ddd, 1H, J22-21,23,24 = 7.0, 5.6, 1.2 Hz, H22), 4.58 (s, 3H, H1), 4.49 (dt, 1H, J18-19,19’ = 12.3, 13 6.2 Hz, H18), 1.07 (d, 6H, J19-18 = 6.2 Hz, H19). C-NMR (151 MHz, acetone-d6, 298K) 200.66 (C6), 159.47 (C25), 157.96 (C21), 157.31 (C14), 156.32 (C26), 152.73 (C7), 138.23 (C23), 137.53 (C28), 134.05 (C10), 132.74 (C11), 127.63 (C22), 126.16 (C3), 124.24 (C12), 123.77 (C24), 122.47 (C27), 121.15 (C8), 121.07 (C9), 119.80 (C13), 119.62 (C4), 70.98 (C18), 36.39 (C1), 20.90 (C19). UV/vis (methanol): λmax, -1 -1 nm (ε, M ·cm )= 280 (12006), 311 (14895), 392 (4700), 463 (4220). ESI-MS (MeOH): m/z = 622.1 ([M-2PF6]). Elemental analysis (% found): C, 39.63; H, 3.24; N, 10.74. Calcd for C30H29F12N7O2P2Ru: C, 39.57; H, 3.21; N, 10.77. II + [Ru (PhthaPz-OMe)(tpm)(OH2)](PF6)2 (4(PF6)2): 3 (120 mg, 0.16 mmol) was dissolved in a 40 mL mixture of acetone and water (1:3). AgBF4 (109 mg, 0.56 mmol) was added into the solution that was then refluxed at 90°C for 4 hours. After cooling to room ® temperature, the reaction crude was filtered through celite to remove the silver chloride formed. The brown filtrate was then concentrated in a rotary evaporator until about 20 mL, followed by centrifugation (10000 rpm, 10 min) in order to remove the remaining solids. To the clear red solution 20 drops of a saturated aqueous NH4PF6 solution were added. The red precipitate formed was filtered off, washed with diethyl ether and dried under vacuum. 1 Yield: 76 mg (55%). H-NMR (600 MHz, acetone-d6, 298K) δ=9.90 (s, 1H, H24), 8.99 (d, 1H, J4-3 = 2.4 Hz, H4), 8.97 (d, 1H, J9-10 = 8.5 Hz, H9), 8.83 (d, 1H, J20-21 = 1.7 Hz, H20), 8.72 (d, 1H, J31-32 = 2.9 Hz, H31), 8.67 (d, 1H, J22-21 = 2.7 Hz, H22), 8.58 (d, 1H, J33-32 =2.0 Hz, H33), 8.53 (d, 1H, J26-27 = 5.5 Hz, H26), 8.47 (d, 1H, J12-11 = 8.1 Hz, H12), 8.29 (dd, 1H, J10-9,11 = 8.2, 7.7 Hz, H10), 8.17 (t, 1H, J11-10,12 = 7.7 Hz, H11), 7.74 (d, 1H, J3-4 = 2.3 Hz, H3), 6.85 (m, J21-20,22 = 2.4 Hz, J28-27 = 2.2 Hz, H21, H28), 6.80 (t, 1H, J32-31,33 = 2.5 Hz, H32), 6.34 (t, 13 1H, J27-26,28 = 2.5 Hz, H27), 4.20 (s, 3H, H18), 3.74 (s, 1H, H1). CNMR (151 MHz, acetone-d6, 298K) 200.22 (C6), 158.58 (C14), 152.76 (C7), 148.70 (C33), 148.04 (C28), 147.06 (C20), 135.74 (C26), 134.89 (C31), 134.17 (C10), 133.64 (C22), 133.40 (C11), 125.84 (C3), 124.48 (C12), 122.02 (C9), 121.75 (C8), 120.96 (C13), 120.61 (C4), 109.06 (C32), 108.69 (C27), 108.04 (C21), 76.61 (C24), 55.38 (C18), -1 -1 36.65 (C1). UV/vis (methanol): λmax, nm (ε, M ·cm )= 295 (8297), 392 (5315). ESI-MS (MeOH): m/z = 575.1 ([M-2PF6]). Elemental analysis (% found): C, 32.02; H, 2.81; N, 16.19. Calcd for C23H24F12N10O2P2Ru: C, 31.99; H, 2.80; N, 16.22. II + trans,fac-[Ru (PhthaPz-OMe)(bpea)(OH2)](PF6)2 (6(PF6)2): 5 (120 mg, 0.16 mmol) was dissolved in a 40 mL mixture of acetone and water (1: 3). AgBF4 (109 mg, 0.56 mmol) was then added into the solution, which was refluxed at 90°C for 4 hours. After cooling to ® room temperature, the reaction crude was filtered through celite to remove the silver chloride formed. The red-brown solution was concentrated in a rotary evaporator until about 20 mL, followed by centrifugation (10000 rpm, 10 min) to remove the remaining solids. To the clear red solution 20 drops of a saturated aqueous NH4PF6 solution were added. The precipitate formed was filtered off, washed with diethyl ether and dried under vacuum. Yield: 96 mg 1 (68%). H-NMR (600 MHz, acetone-d6, 298K) δ=8.99 (d, 1H, J4-3 = 2.4 Hz, H4), 8.96 (d, 1H, J34-33 = 5.3 Hz, H34), 8.93 (m, 2H, H20, H9), 8.36 (d, 1H, J12-11 = 8.1 Hz, H12), 8.23 (t, 1H, J10-9,11 = 7.7 Hz, H10), 8.08 (t, 1H, J11-10,12 = 7.6 Hz, H11), 7.99 (td, 1H, J32-33,31 = 7.8, J32-34 = 1.4 Hz, H32), 7.88 (td, 1H, J22-23,21 = 7.4, J22-20 = 1.7 Hz, H22), 7.72 (d, 1H, J3-4 = 2.4 Hz, H3), 7.67 (d, 1H, J31-32 = 7.9 Hz, H31), 7.57 (m, 1H, H33), 7.55 (d, 1H, J23-22 = 7.9 Hz, H23), 7.50 (t, 1H, J21-22,20 = 6.6 Hz, H21), 4.57-4.40 (m, 4H, H25, H29), 3.71 (s, 3H, H1), 3.65 (s, 3H, H18), 2.40 (m, 1H, J27-27’,28 = 9.2, 5.0 Hz, H27), 2.30 (m, 1H, J27’-27,28 = 9.2, 5.0 Hz, 13 H27’),0.91 (t, 3H, J28-27,27’ = 7.0 Hz, H28). C-NMR (151 MHz, acetone-d6, 298K) 202.85 (C6), 161.20 (C24), 159.56 (C30), 158.81 (C14), 151.85 (C7), 149.37 (C20), 147.67 (C34), 137.42 (C32), 136.72 (C22), 134.06 (C10), 132.67 (C11), 125.82 (C3), 124.41 (C12), 124.30 (C21), 123.78 (C33), 121.63 (C8), 121.54 (C23), 121.49 (C31), 121.35 (C9), 120.47 (C13), 119.89 (C4), 67.89 (C25), 67.29 (C29), 62.80 (C27), 54.19 (C18), 35.89 (C1), 7.97 (C28). UV/vis (methanol): λmax, -1 -1 nm (ε, M ·cm )= 299 (5810), 423 (5753). ESI-MS (MeOH): m/z = 586.1 ([M-2PF6]). Elemental analysis (% found): C, 37.06; H, 3.60; N, 11.15. Calcd for C27H31F12N7O2P2Ru: C, 36.99; H, 3.56; N, 11.19. Acknowledgements 14 | J. Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx Please do not adjust margins Please do not adjust margins Journal Name ARTICLE Support form MINECO (CTQ2011-26440 and CTQ2015-64261R) is gratefully acknowledged. M.G.-S. is grateful for the award of a PIF doctoral grant from UAB. Notes and references 1 W. A. Herrmann and C. 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