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

Half-Sandwich Nickelacarboranes Derived from [7-(MeO(CH2)2S)-7,8-C2B9H11]−

New carboranyl thioethers 1-MeO(CH2)nS-1,2-C2B10H11 (n = 2, 3) were prepared by the alkylation of the trimethylammonium salt of 1-mercapto-ortho-carborane with 1-bromo- 2-methoxyethane and 1-bromo-3-methoxypropane, respectively. Their deboronation with cesium fluoride in ethanol gave the corresponding nido-carboranes Cs[7-MeO(CH2)nS-7,8-C2B9H11] (n = 2, 3). The reactions of Cs[7-MeO(CH2)2S-7,8-C2B9H11] with various nickel(II) phosphine complexes [(dppe)NiCl2] and [(R’R2P)2NiCl2] (R = R’ = Ph, Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) were studied and a series of nickelacarboranes 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 and 3,3- (R’R2P)2-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 (R = R’ = Bu; R = Me, R’ = Ph; R = Ph, R’ = Me, Et) was prepared. The molecular crystal structure of 3,3-dppe-1-MeO(CH2)2S-closo-3,1,2-NiC2B9H10 was determined by single-crystal X-ray diffraction.

Synthesis and Catalytic Properties of Novel Ruthenacarboranes Based on nido-[5-Me-7,8-C2B9H10]2− and nido-[5,6-Me2-7,8-C2B9H9]2− Dicarbollide Ligands

The effect of methyl substituents in the lower belt of dicarbollide ligands on the redox potential of ruthenacarboranes based thereof, as well as the ability of the metallacarboranes obtained to catalyze radical polymerization with atom transfer were studied. For this purpose, a new approach to the synthesis of closo-ruthenacarboranes based on substituted dicarbollide ligands was developed and six new complexes 3,3-(Ph2P(CH2)4PPh2)-3-H-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H9, 3,3,8-(Ph2P(CH2)4PPh-μ-(C6H4-o))-3-Cl-9-Me-12-X-closo-3,1,2-RuC2B9H8 and 3,3,4,8-(Ph2P(CH2)4P-μ-(C6H4-o)2)-3-Cl-9-Me-9-X-closo-3,1,2-RuC2B9H7 (X = H, Me) were synthetized and characterized by single crystal X-ray diffraction, NMR and ESR spectroscopy and MALDI TOF mass-spectrometry. Comparison of the values of the redox potentials of the synthesized ruthenium complexes in 1,2-dichloroethane with the values previously found for the corresponding ruthenacarboranes based on the parent dicarbollide anion showed that the introduction of methyl substituents into the carborane cage led to a decrease in the redox potentials of the complexes, which made them more preferable catalysts for ATRP. Test experiments on the polymerization of MMA showed that the synthesized ruthenacarboranes were effective catalysts for ATRP, the most active being the complex with two methyl groups and two ortho-phenylenecycloboronated fragments.