On the role of catalyst components in the living metathesis polymerization of substituted acetylenes by MoOCl₄-based systems

The role of components in MoOCl₄-based living polymerization catalysts was studied. The MALDI TOF MS spectra of the poly(o-[(trifluoromethyl)phenyl]acetylene)s prepared with n-Bu₄Sn and Et₃A1 as cocatalysts suggested a difference of 28(C₂H₄) in polymer molecular weight. This indicates that the formed polymer possesses an alkyl group of cocatalyst in the initiating chain end, which implies the transalkylation between MoOCl₄ and a cocatalyst and the subsequent formation of a Mo carbene. Sterically uncrowded aliphatic alcohols were useful as the third catalyst components. Addition of EtOH to the catalyst system led to the increase of activation enthalpy and the change of activation entropy from a negative to positive value in the propagation reaction, which suggests that EtOH coordinates to the propagating end competitively with the monomer.