Bisphosphine Monoxide-Ligated Ruthenium Catalysts: Active, Versatile, Removable, and Cocatalyst-Free in Living Radical Polymerization

As potentially bidentate ligands, bisphosphine monoxides [BPMOs, Ph2P(O)(CH2)nPPh(2)) n = 1, 2, Ph = C6H5] were found to be effective for pentamethylcyclopentathene ruthenium chloride catalysts [Cp*(RuCl)-Cl-II(BPMO)(m), m = 1,2] in living radical polymerization active, versatile, cocatalyst-free, and removable The complexes catalyzed lime radical polymerizations of a variety of monomers and their functionalized derivatives methyl acrylate, methyl methacrylate (M M A). styrene, 2-hydroxyethyl methacrylate, and poly(ethylene glycol) methacrylate The controllability and activity were high enough even with a small amount of catalyst ([Ru](0)/[initiator](0) = 1/200, 50 ppm for monomer), to give high molecular weight PM M A with narrow MWD (M-n = 103 000 M-w/M-n = 1 19) and block copolymers Such an activity and a wide applicability in terms of monomers have been found for few Ru catalysts thus far. Importantly, they did not necessarily need a cocatalyst (aluminum alkoxide, amine. etc) for their catalysis, in contrast to most of the other ruthenium catalysts that are effective only with a cocatalyst. The cocatalyst-free catalysis is concluded to be derived from the phosphine oxide moiety in BPMO, whose hemilabile coordination promotes the deactivation process (in growth active) [similar to similar to similar to C center dot (growth active) -> -C-Cl (dormant)] and, in turn, accelerates the whole catalytic cycle (radical <-> dormant, Ru-II <-> Ru-III) Furthermore, the high polarity of BPMO ligands effectively helped near perfect removal of the catalyst residue ( >99 7% for PM MA) just by single reprecipitation into methanol