Efficient catalytic systems based on paramagnetic closo-ruthenacarboranes for the controlled synthesis of polymers

Novel catalytic systems were proposed for controlled radical polymerization of vinyl monomers. These systems are based on the paramagnetic (17-electron) closo-complex, namely, 3,3-(dppb)-3-Cl-closo-3,1,2-RuC2B9H11 (1, dppb is 1,4-bis(diphenylphosphino)butane) and its mono(P-phenylene)- and di(P,P-ortho-phenylene)cycloboronated derivatives, namely, (R = H, n = 10 (2); R = Me, n = 8 (3)) and (4). With the polymerization of methyl methacrylate as an example, the effect of the steric hindrances in complexes 1-4 on the synthesis and molecular-weight characteristics of the resulting polymers was analyzed. In the presence of aliphatic amines, the polymerization rate increases substantially and the catalyst concentration can be lowered without losing control of the process. The structure of 17-electron complex 3 in the solid state and its paramagnetic nature were confirmed by X-ray diffraction and ESR spectroscopy.