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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-[PPh2(CH2)5PPh2]-3-Cl-3,1,2-closo-RuC2B9H11 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.

The heating of a mixture of 14-e [Ph2P(CH2)nPPh2]FeCl2 (n = 3 or 2) with the [K]+ salt of the [nido-7,8-C2B9H12]− mono-anion under gentle reflux in benzene affords either the paramagnetic (17-electron) complex [3,3-(dppp)-3-Cl-closo-3,1,2-FeC2B9H11] isolated in 15% yield or a mixture of the paramagnetic complex [3,3-(dppe)-3-Cl-closo-3,1,2-FeC2B9H11] (46% yield) and the diamagnetic complex [commo-8,8′-μ-(Ph2PCH2CH2PPh2)-3,3′-Fe{1,2-C2B9H10}2] (10% yield). All three novel ferracarboranes were characterized by spectroscopic (EPR or NMR) data and single-crystal X-ray diffraction.

The ruthenacarborane complexes of the exo-nido- and closo-structure, namely, diamagnetic exo-nido-5,6,10-[RuCl(PPh3)2]-5,6,10-(μ-H)3-10-H-7,8-(CH3)2-7,8-C2B9H6, 3,3-[Ph2P(CH2)nPPh2]-3-H-3-Cl-closo-3,1,2-RuC2B9H11 (n = 4, 5), paramagnetic 3,3-[Ph2P(CH2)nPPh2]-3-Cl-closo-3,1,2-RuC2B9H11 (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 {C2B9} 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.

Reactions of [ exo -5,6,10-{Cl(Ph 3 P) 2 Ru}-5,6,10-(μ-H) 3 -10-H- nido -7,8-C 2 B 9 H 8 ] ( 1 ) with 1,5-bis(diphenylphosphino)pentane ( 2 ) in benzene either at ambient temperature for ca 2 days or under gently reflux for 30 min in anaerobic conditions both proceed with the replacement of PPh 3 ligands on the ruthenium center with the diphosphine to form diamagnetic (18-electron) closo complex [3,3-{κ 2 -{Ph 2 P(CH 2 ) 5 PPh 2 }}-3-Cl-3-H- closo -3,1,2-RuC 2 B 9 H 11 ] ( 3 ). On heating in benzene, 3 in the presence of a small amount of CCl 4 affords stable paramagnetic (17-electron) species [3,3-{κ 2 -{Ph 2 P(CH 2 ) 5 PPh 2 }}-3-Cl- closo -3,1,2-RuC 2 B 9 H 11 ] ( 5 ) along with traces of ortho -phenylenecycloboronated closo complex, ( 7 ). The latter complex was prepared in higher yields by thermal treatment of either 3 or 5 under more severe conditions in toluene at 110 °C. Thermolysis of 7 in boiling toluene in the presence of a small amount of CCl 4 afforded the new paramagnetic complex ( 8 ), featuring bis( ortho -cycloboronation) of both P-phenyl groups located at the same phosphorus atom of the ruthenium bound dppt ligand; a minor amount of chloro-cage-substituted complex ( 9 ) was also isolated from the latter reaction as the by-product. All new closo -ruthenacarboranes obtained were characterized by a combination of analytical, multinuclear NMR (for even-electron species) or EPR (for odd-electron species) data and, in addition, by single-crystal X-ray diffraction studies of three paramagnetic complexes 5 , 7 and 8 .

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.