Palladium/IzQO-Catalyzed Coordination–Insertion Copolymerization of Ethylene and 1,1-Disubstituted Ethylenes Bearing a Polar Functional Group

Coordination–insertion copolymerization
of ethylene with
1,1-disubstituted ethylenes bearing a polar functional group, such
as methyl methacrylate (MMA), is a long-standing challenge in catalytic
polymerization. The major obstacle for this process is the huge difference
in reactivity of ethylene versus 1,1-disubstituted ethylenes toward
both coordination and insertion. Herein we report the copolymerization
of ethylene and 1,1-disubstituted ethylenes by using an imidazo­[1,5-a]­quinolin-9-olate-1-ylidene-supported palladium catalyst.
Various types of 1,1-disubstituted ethylenes were successfully incorporated
into the polyethylene chain. In-depth characterization of the obtained
copolymers and mechanistic inferences drawn from stoichiometric reactions
of alkylpalladium complexes with methyl methacrylate and ethylene
indicate that the copolymerization proceeds by the same coordination–insertion
mechanism that has been postulated for ethylene.