Living ring-opening metathesis polymerization of bicyclo[3.2.0]heptene catalyzed by a ruthenium alkylidene complex

Abstract

Living polymerizations using ring-opening metathesis catalysts (ROMP) have allowed the synthesis of polymers with controlled structure and properties. In the past few years, efforts have been focused on developing novel transition-metal alkylidene complexes that catalyze this reaction and provide either access to new product or easier synthesis. All of the catalysts developed to date are high oxidation state organometallic complexes, which exhibit limited tolerance to polar functional groups, and only catalyze the living polymerization of norbornene and its derivatives. Recently, we have synthesized a ruthenium alkylidene complex that exhibits exceptional tolerance to a variety of polar functional groups and also catalyzes the living ROMP of norbornene. Because we were interested in elucidating the details of this living polymerization, we investigated the ROMP of highly reactive monomer bicyclo[3.2.0] heptene (I), catalyzed by the late-transitionmetal complex (PPh_3)_2(Cl)_2Ru(=CHCH=CPh_2) (II; eq 1). We hope that an investigation of this system will provide us with a better understanding of the mechanism of polymerization catalyzed by late-transition-metal alkylidene complexes and eventually allow us to control molecular weight in the preparation of functionalized polymers with potential uses in biological applications.