Mononuclear closo-ruthenacarborane complexes containing a rare eight-membered metal-diphosphine ring

Reactions of [exo-5,6,10-{Cl(Ph3P)2Ru}-5,6,10-(μ-H)3-10-H-nido-7,8-C2B9H8] (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 PPh3 ligands on the ruthenium center with the diphosphine to form diamagnetic (18-electron) closo complex [3,3-{κ2-{Ph2P(CH2)5PPh2}}-3-Cl-3-H-closo-3,1,2-RuC2B9H11] (3). On heating in benzene, 3 in the presence of a small amount of CCl4 affords stable paramagnetic (17-electron) species [3,3-{κ2-{Ph2P(CH2)5PPh2}}-3-Cl-closo-3,1,2-RuC2B9H11] (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 CCl4 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.