Ruthenium carborane complexes: a relationship between the structure, electrochemical properties, and reactivity in catalysis of polymerization processes.

The ruthenacarborane complexes of the exo-nido- and closo-structure, namely, diamagnetic exo-nido-5,6,10-[RuCl(PPh)]-5,6,10-(μ-H)-10-H-7,8-(CH)-7,8-CBH, 3,3-[PhP(CH)PPh]-3-H-3-Cl- closo-3,1,2-RuCBH ( n = 4, 5), paramagnetic 3,3-[PhP(CH)PPh]-3-Cl- closo-3,1,2-RuCBH ( n = 2-5), and their some ortho-phenylenecycloboronated derivatives, were studied by cyclic voltammetry. All chelate closo-complexes are characterized by reversible redox transitions, while the exo-nido-complex is liable to irreversible oxidation. Shortening of the methylene link in the diphosphine ligand of closo-ruthenacarboranes and/or the introduction of ortho-phenylenecycloboronated moieties and methyl substituents to the carbon atoms of the {CB} ligand lead to a decrease in the redox potential and electron density redistribution to the metal atom. A comparison of the experimental results on methyl methacrylate polymerization in the presence of the catalytic systems based on the studied metallacarboranes with the data on their electrochemical characteristics suggests that the efficiency of using the ruthenium complexes as catalysts is mainly determined by steric factors. [ABSTRACT FROM AUTHOR]