Diene-Capped Carbene: Pathways to Cycloaddition, Copolymerization, and Catalysis

An unprecedented diene-capped carbene (DECC), DieneIPr (2) [{(H2CC)­NDipp}2C:; Dipp = 2,6-iPr2C6H3] is accessed by a convenient oxidation/double-deprotonation pathway starting from a widely utilized N-heterocyclic carbene. Functionalization of the carbene donor site in 2 with Se (3) and PPh (5) revealed exceptional π-accepting character within the carbene unit. The phosphinidene complex DieneIPrPPh (5) undergoes diene-localized [4 + 2] cycloaddition with cyclooctyne, while anionic copolymerization of 5 with isoprene yields a “natural rubber”-type copolymer (11) that becomes an active alkyne hydration precatalyst upon P atom coordination to gold.