Pd Complex-catalyzed copolymerization of a bicyclic methylenecyclopropane with carbon monoxide to afford a new polyketone

Alternating copolymerization of 7-methylenebicyclo[4,1,0]heptane with CO in thf is promoted by catalysts prepared from Pd complexes, PdCl (Me)L (L = chelating diimine or diamine), and NaBARF (BARF =[B{C6H3(CF3)2-3,5}4]–), to produce the polyketone containing enone and 1,2cyclohexane units. The Pd complexes with Schiff-base type diimines, 2,9-disubstituted 1,10-phenanthroline, and tmen are effective as catalysts to afford the polyketone containing mainly the cis-1,2-disubstituted cyclohexane ring. Polymerization in thf using Schiff-base diimine as the ligand for Pd produces product with a narrow molecular weight distribution (Mw/Mn= 1.10–1.19). The increase in molecular weight during polymerization and polymer growth caused by addition of new monomer indicates living polymerization. The reaction catalyzed by cationic Pd complexes with 2,2ʹ-bipy and phen, prepared from NaBARF and PdCl(Me)L (L = 2,2ʹ-bipy, phen) in CH3CN, produces polymer that contains both trans- and cis-disubstituted cyclohexane rings in almost equal amounts. Heating of the polymer with cis-disubstituted cyclohexane in the presence of sodium o-chlorophenolate induces epimerization of the polymer into thermodynamically more stable polyketones with transdisubstituted cyclohexane.