Carborane complexes of ruthenium with long-chain diphosphine ligands as effective catalysts of controlled radical polymerization

Catalytic systems based on carborane complexes of ruthenium with long-chain diphosphine ligands, such as 1,4-bis(diphenylphosphino)butane and 1,5-bis(diphenylphosphino)pentane, are prepared for the controlled radical polymerization of methyl methacrylate. It is found that the used metallacarboranes can catalyze polymerization initiated by both carbon tetrachloride and 2,2′-azo-bis(isobutyronitrile). It is shown that closo -ruthenacarborane with 1,5-bis(diphenylphosphino)pentane 3,3-[PPh 2 (CH 2 ) 5 PPh 2 ]-3-Cl-3,1,2- closo -RuC 2 B 9 H 11 and its o -phenylenecycloborated derivatives make it possible to conduct polymerization at higher rates than those attained with the use of previously synthesized complexes based on diphosphines with a smaller length of the hydrocarbon fragment. The relationship between the redox potential of the complex and the efficiency of control over molecular-mass characteristics of the polymers is analyzed. Experiments reveal that the addition of small amounts of aliphatic amines causes a considerable increase in the rate of polymerization and leads to a decrease in the concentration of the catalyst with retention of a high degree of control over the process.