Unexpected E-to-Z Isomerizations during the Negishi-Type Homocoupling of E-Iodoalkenes

Abstract

The direct insertion of Zn into olefin–halide bonds is a challenge. When (E)-alkenyl iodides were treated with a very large excess of Zn nanoparticles, in the presence of Pd(PPh3)4, the dimerization was observed but, unexpectedly, yielding mainly Z,E-1,3-dienes. This apparently contrathermodynamic E-to-Z isomerization of organometallic intermediates is predicted to be general and is explained with the aid of DFT [principally M06/6-311+G(d,p)], MP2, and CCSD(T) calculations.