Sterically Reduced Cyclopentadienyl, Amidinate Group 4 Metal Initiators for Living Coordination Chain-Transfer Polymerization with Challenging Metals and Monomers

Reduction of nonbonded steric interactions within the supporting cyclopentadienyl, amidinate (CPAM) ligand environment of group 4 metal dimethyl complexes of general formula, (η5-C5R5)[κ2-(N,N)-N(R1)C(R2)N(R3)]MMe2 (I), render these capable of serving as initiators for the living coordination polymerization (LCP) and living coordinative chain-transfer polymerization (LCCTP) of challenging alkene monomers, such as vinylcyclohexene (VCH). More specifically, the active ion pair initiator derived from the Cs-symmetric Hf preinitiator 1 (M = Hf; R = R1 = R3; R2 = Ph) and the anilinium borate co-initiator, [PhNHMe2][B(C6F5)4] (B1), provides isotactic poly(vinylcyclohexane) (iPVCH) through LCP via a chain-end stereocontrol mechanism, and in the presence of 5 equiv of diethylzinc (ZnEt2) as a chain-transfer agent, the LCCTP of VCH provides end-group-functionalized atactic PVCH using a reactive quench with I2. Finally, the active initiator obtained from the CPAM Ti preinitiator 2 (M = Ti; R = H, R1 = R3 = Me, R2 = Ph) and either B1, [Ph3C][B(C6F5)4] (B2), or B(C6F5)3 (B3) as a co-initiator, was shown to be competent for the nonliving coordination polymerizations of ethene, propene, and 1-hexene.