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

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 .