"This is the peer reviewed version of the following article: [Chem.  Eur. J . 2015,  21, 7 144  – 7 150   ], which has been published in final form at [http://onlinelibrary.wiley.com/doi/10.1002/chem.201500333/abstract]. This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving ."     Highly  Efficient  Chirality  Transfer  from  Diamines  Encapsulated  within  a  Self-­‐Assembled  Calixarene-­‐Salen  Host   Luis  Martínez-­‐Rodríguez,[a]  Nuno  A.  G.  Bandeira,[a]  Carles  Bo[a,b]  and  Arjan  W.  Kleij*[a,c]     Abstract:  A  calix[4]arene  host  equipped  with  two  bis-­‐ Zn(salphen)  complexes  self-­‐assembles  into  a  capsular   complex  in  the  presence  of  a  chiral  diamine  guest  with   an  unexpected  2:1  ratio  between  the  host  and  the   guest.  Effective  chirality  transfer  from  the  diamine  to   the  calix-­‐salen  hybrid  host  is  observed  by  CD   spectroscopy,  and  a  high  stability  constant  K21  of  1.59   ×  1011  M-­‐2  for  the  assembled  host-­‐guest  ensemble  has   been  determined  with  a  substantial  cooperativity   factor  a  of  6.4.  DFT  analysis  has  been  used  to   investigate  the  origin  of  the  stability  of  the  host-­‐guest   system  and  the  experimental  CD  spectrum  compared   with  the  calculated  ones  for  both  possible   diastereoisomers  showing  that  the  M,M-­‐isomer  is  the   one  that  is  preferentially  formed.  The  current  system   holds  promise  for  the  chirality  determination  of   diamines  as  evidenced  by  the  investigated  substrate   scope  and  the  linear  relationship  between  the  ee  of   the  diamine  and  the  amplitude  of  the  observed   Cotton  effects.   Introduction   The  creation  and  transfer  of  chirality,  sometimes   [a] [b] [c] L. Martínez, Dr. N. A. G. Bandeira, Prof. Dr. C. Bo, Prof. Dr. A. W. Kleij, Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain E-mail: akleij@iciq.es Prof. Dr. C. Bo Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo s/n, 43007 Tarragona, Spain Prof. Dr. A. W. Kleij Catalan Institute of Research and Advanced Studies (ICREA), Pg. Lluís Companys 23, 08010 Barcelona, Spain Supporting information for this article is given via a link at the end of the document referred  to  as  chirogenesis,  plays  a  key  role  in   biological  processes  that  involve  proteins  and  other   natural  systems  such  as  DNA.[1]  Chiral  transmission   has  also  been  shown  to  be  crucial  in  the  catalytic   asymmetric  synthesis  of  various  organic  compounds,   where  a  metal  or  organic  catalyst  favors  the  formation   of  one  preferred  chiral  product  in  the  enantio-­‐ controlling  step.[2]  Further  to  this,  to  date  highly   efficient  methodologies  have  been  designed  to  create   materials  with  reversible  and  responsive  features,  and   smart  materials  have  also  been  developed  with  pre-­‐ designed  sensing  purposes.[3]  The  field  of  chirality   sensing  has  rapidly  advanced  over  the  last  five  years   with  a  strong  focus  on  newly  designed  systems  that   may  facilitate  fast  and  efficient  determination  of  the   concentration,  absolute  configuration,  enantiomeric   excess  and/or  molecular  identity  of  a  chiral  analyte.[4]   Whereas  bis-­‐porphyrins  have  been  and  still  continue   to  be  popular  hosts  in  chirality  transfer  processes,[4e,5]   we  have  recently  started  to  use  modular  and  easy  to   assemble  dinuclear  and  trinuclear  Zn(salen)  based   hosts  that  show  (strong)  chirogenesis  effects  in  the   presence  of  chiral  carboxylic  acids,[4d]  diamines,   aminoalcohols  and  diols[6]  induced  by  1:1  complex   formation  between  the  host  and  the  guest.   With  most  reported  supramolecular  host  systems,  the   transfer  of  chiral  information  by  interaction  with   chiral  diamines  is  hampered  by  the  requirement  of  a   pre-­‐treatment  of  the  analyte  with  additives,  the  use  of   a  (large)  excess  of  diamine,  the  requirement  of  air-­‐ sensitive  reagents  and/or  a  relatively  low  binding   constants  between  the  host  and  guest  partners;  such   challenges  makes  the  quest  for  an  efficient  host   system  still  an  important  undertaking.       Scheme  1.  Schematic  structures  of  calix-­‐Zn(salphen)   hosts  1  and  2  and  the  expected  coordination   stoichiometry  (1:1)  and  induction  of  chirality  in  host  1   by  binding  to  a  one  molecule  of  a  ditopic  chiral   diamine.   Here,  we  present  a  new  type  of  supramolecular  host   for  chiral  diamine  guests  that  is  based  on  a   calix[4]arene-­‐salen  hybrid  structure.  Each  calixarene   unit  is  functionalized  by  two  distal  Zn(salphen)   complexes  connected  to  the  upper  rim  of  the   calixarene  incorporating  two  pro-­‐chiral  biphenyl  units   (Scheme  1;  host  1).  These  Zn(salphen)  complexes  are   known  to  form  stable  complexes  with  amine  donors[7]   and  as  such  we  anticipated  the  easy  formation  of  1:1   complexes  with  chiral  diamines;  i.e.,  complex  1  would   thus  be  engaged  with  one  diamine.  However,  the   unusual  formation  of  2:1  host/guest  assemblies  with   two  molecules  of  calixarene-­‐bis-­‐Zn(salphen)s  are   interacting  with  only  one  diamine  was  noted  with   concomitant,  cooperative  and  diastereo-­‐selective   encapsulation  of  the  chiral  diamine  guest.  The   underlying  reasons  for  this  unusual  observation  have   been  investigated  in  detail  using  various  experimental   and  computational  methods,  and  the  use  of  these   types  of  calix-­‐salen  host  systems  in  the  determination   of  the  absolute  configuration  and  ee  of  the  diamine  is   also  detailed.     Results  and  Discussion   represents  a  control  compound  in  the  chirality   transfer  experiments  as  will  be  discussed  below.   We  first  designed  host  1  (Scheme  2  and  Schemes  S1-­‐ S2;  Supporting  Information  for  more  details;  Figures   S1-­‐16)  having  two  co-­‐facially  orientated  Zn(salphen)   units  that  should  accommodate  the  binding  of   suitable  chiral  diamine  guests  and  block  the  Caryl-­‐Caryl   rotation  of  the  biphenyl  units  leading  to  chirality   transfer  effects.         Scheme  2.  Synthesis  of  bis-­‐Zn(salphen)  host  1  and   schematic  structures  for  chiral  diamines  a  and  b.   The  synthesis  of  host  1  started  off  by  using  known   calixarene-­‐disalicylaldehyde  A-­‐1  and  treatment  with   the  ketamine  reagent  B  (Scheme  S1)  furnishing  the   calixarene-­‐bis-­‐salphen  ligand  B-­‐1  in  70%  yield.  The  Zn   based  host  1  was  then  prepared  from  B-­‐1  by  reaction   with  a  stoichiometric  amount  of  ZnEt2  in  THF  giving   the  desired  calixarene-­‐bis-­‐Zn(salphen)  complex  in  83%   yield.  Likewise,  the  mono-­‐Zn  host  2  (Scheme  S2)  was   prepared  in  a  similar  way  in  99%  yield  from  its   calixarene-­‐mono-­‐salphen  precursors.  Complex  2   The  potential  induction  of  chirality  by  chiral  diamines   and  thus  a  conformational  control  within  host   structure  1  was  first  probed  in  the  presence  of   (1R,2R)-­‐(+)-­‐1,2-­‐diphenylethylenediamine  a  (Scheme  2)   and  the  UV-­‐vis  and  circular  dichroism  (CD)  features  of   1  in  the  presence  of  this  chiral  diamine  were  studied.   Titration  of  a  solution  of  1  (CH2Cl2;  6  ×  10-­‐5  M)  with  a   solution  of  the  diamine  a  (CH2Cl2;  6  ×  10-­‐4  M)  showed   typical  UV-­‐vis  changes  of  a  Zn(salphen)  derived   complex  (Figure  1a).  A  small  but  detectable   bathochromic  shift  (Dl  =  6  nm)  was  noted  together   with  a  significant  decrease  of  the  absorption  upon   addition  of  higher  amounts  of  diamine  a.  Similar  types   of  bathochromic  shifts  of  Zn(salphen)s  were  noted  in   the  presence  of  pyridine  donors,[8]  however  in  these   cases  an  increasing  absorption  was  noted  at  higher   concentrations  of  analyte  due  to  aggregate-­‐to-­‐ monomer  transitions  of  these  materials.  Thus,  in  the   present  case  it  seems  that  host  molecule  1  does  not   seem  to  be  in  an  aggregated  state  rendering  it  useful   for  interaction  with  suitable  ditopic  substrates  such  as   diamine  a.  The  CD  features  of  (Figures  1b  and  1d)  1   showed  typical  Cotton  effects  at  l  =  416  and  476  nm   with  an  unexpected  saturation  point  after  the   addition  of  0.5  equiv  of  diamine  a,  i.e.  at  a  2:1  host-­‐ guest  ratio  (Figure  1c).[9]  The  species  formed  at  this   ratio  proved  to  be  rather  stable  as  a  large  excess  of  40   equiv  of  the  diamine  guest  are  required  to  fully   disrupt  the  2:1  assembly  (Supporting  Information;   Figure  S28).     (a) (d) cooperative  binding  of  a  (full  details  in  the  Supporting   Information).  Interestingly,  a  similar  preferred  2:1   stoichiometry  between  host  1  and  diamines  b  and  d   (Figures  S29-­‐S32)  was  found  as  evidenced  by  their   titration  data,  thus  pointing  to  more  general  and   similar  chirality  transfer  behaviour  for  1  in  the   presence  of  chiral  diamines.   20 Δε / mdeg 10 0 -10 -20 360 (b) 400 440 480 520 λ / nm (e) (c)     Figure  1.  a)  Zoom  of  the  UV-­‐vis  spectrum  for  1  (6  ×  10-­‐ 5  M;  CH2Cl2)  in  the  presence  of  increasing  amounts  of   diamine  a  (0-­‐100  eq).  b)  CD  spectral  changes  for  host   1  (6  ×  10-­‐5  M;  CH2Cl2)  in  the  presence  of  0.06-­‐1.50   equiv  of  diamine  b.  c)  Titration  curve  for  1  using  the   CD  data  at  l  =  416  nm.  d)  CD  response  for  1  in  the   presence  of  0.5  equiv  of  diamine  a  at  [1]  =  2  ×  10-­‐4  M   (CH2Cl2).  e)  Computed  structure  for  assembly  (1)2·∙b.   The  binding  constant  K2,1  represents  the  binding  of   one  diamine  with  two  equiv  of  calixarene  host  1;  if   this  binding  process  is  cooperative  (i.e.,  K1,1