d⁰/fⁿ-mediated ring-opening Ziegler polymerization (ROZP) and copolymerization with mono- and disubstituted methylenecyclopropanes. Diverse mechanisms and a new chain-capping termination process

The mono- and disubstituted methylenecyclopropane derivatives 2-phenyl-1-methylene-cyclopropane (A) and 7-methylenebicyclo[4.1.0]heptane (B) have been successfully implemented in ring-opening Ziegler polymerization. Homogeneous ethylene + 2-phenyl-1-methylenecyclopropane (A) random copolymerizations are mediated efficiently by the single-site catalysts Cp*₂ZrMe⁺B(C₆F₅) ₄^-, [Cp*₂LuH]₂, [Cp*₂SmH]₂, and [Cp*₂ YH]₂ (Cp* = C₅Me₅) to produce a copolymer (C) with A enchained in a ring-opened fashion. Single-site coordinative polymerization of 7-methylenebicyclo[4.1.0]heptane (B) proceeds via either ring-opened or ring-unopened pathways. In the presence of Cp*₂ZrMe⁺ MeB(C₆F₅) ₃^- at 0°C, B undergoes polymerization to afford the insoluble, ring-unopened homopolymer D, which was characterized by CPMAS NMR, DSC, elemental analysis, FTIR, TGA, and XRD. The melting point of polymer D lies above its decomposition temperature (> 300°C). Random copolymerizations of B and ethylene mediated by Cp*₂ ZrMe⁺MeB(C₆F₅)₃^- at room temperature result in polymer E, a polyethylene capped by a ring-opened B fragment. The formation of B-capped polymer E is a consequence of a new chain transfer mechanism, as evidenced by a linear relationship between M_n and [B]^-1. The rate constant for insertion of ethylene is ∼25× greater than the rate constant for insertion of monomer B into the metal-alkyl bond. Random copolymers (F) of ring-opened B and ethylene are produced when the catalysts Me₂Si(Me₄C₅)(^tBuN)ZrMe₂, Me₂Si(Me₄C₅)(^tBuN)TiMe₂ (activated by either (C₆H₅)₃C⁺ B(C₆F₅)₄^- or B(C₆F₅)₃), and [Cp*₂LuH]₂ are employed.