Acrylonitrile Polymerization by Cy₃PCuMe and (Bipy)₂FeEt₂

Cy₃PCuMe (1) undergoes reversible ligand redistribution at low temperature in solution to form the tight ion pair [Cu(PCy₃)₂][CuMe₂] (3). The structure of 3 was assigned on the basis of (i) the stoichiometry of the 1 = 3 equilibrium, (ii) the observation of a triplet for the PCy₃ C1 ¹³C NMR resonance due to virtual coupling to two ³¹P nuclei, and (iii) reverse synthesis of 1 by combining separately generated Cu(PCy₃)₂⁺ and CuMe₂^- ions. Complex 1 and [Cu(PCy₃)₂][PF₆] (5) coordinate additional PCy₃ to form (Cy₃P)₂CuMe and [Cu(PCy₃)₃][PF₆], respectively, while 3 does not. Complex 1, free PCy₃, and (bipy)₂FeEt₂ (2) each initiate the polymerization of acrylonitrile. In each case, the polyacrylonitrile contains branches that are characteristic of an anionic polymerization mechanism. The major initiator in acrylonitrile polymerization by 1 is PCy₃, which is liberated from 1. A transient iron hydride complex is proposed to initiate acrylonitrile polymerization by 2.