Аннотация:Novel ruthenacarborane 3,3-(Ph2P(CH2)4PPh2)-3-H-3-Cl-9-Me-closo-3,1,2-RuC2B9H10 (1) and its derivatives 3,3-(Ph2P(CH2)4PPh2)-3-Cl-9-Me-closo-3,1,2-RuC2B9H10 (2), 3,3,8-(Ph2P(CH2)4PPh (3) and 3,3,4,8-(Ph2P(CH2)4P-(C6H4-о)2-3-Cl-9-Me-closo-3,1,2-RuC2B9H8 (4) were successfully obtained basing on a nido-carborane ligand bearing methyl substituent in lower bend of the cage [5-Me-7,8-C2B9H11]–. The obtained ruthenacarboranes keep the geometries and steric configurations typical for its unsubstituted analogues but are characterized by lower values of Ru(II)–Ru(III) redox potentials. It was shown that the obtained derivatives are active catalysts of controlled radical polymerization of MMA via ATRP mechanism.