Ligand-displacement reactions as a powerful route to closo-ruthenacarboranes incorporating bidentate N-donor ligands

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

“…In several recent reports we have demonstrated that the long-known "threebridge" exo-nido-ruthenacarborane [exo-5,6,10-{Ru(Ph 3 P) 2 Cl}-5,6,10-(m-H) 3 -10-H-nido-7,8-C 2 B 9 H 8 ] (1) [5], as well as its closo isomer [3,3-(Ph 3 P) 2 -3-Cl-3-H-closo-3,1,2-RuC 2 B 9 H 12 ] [3], can undergo facile substitution of the PPh 3 by the chelating diphosphinoalkanes [Ph 2 P(CH 2 ) n PPh 2 ] (n ¼ 2e4) [3,6] or their chiral derivatives [7,8], as well as by N,N-donor ligands such as 2,2 0 -bipyridyl derivatives [9]. As a result a series of novel diamagnetic (18-electron) and paramagnetic (17-electron) diphosphine and diamine ruthenacarborane complexes of closo and/or exo-nido types have been conveniently prepared, and some of them proved to be extremely efficient pre-catalysts for atom transfer radical polymerization (ATRP) of vinyl monomers [10].…”

“…On heating in benzene, 3 in the presence of a small amount of CCl 4 affords stable paramagnetic (17-electron) species [3,3-{k 2 -{Ph 2 P(CH 2 ) 5 PPh 2 }}-3-Clcloso-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 oddelectron species) data and, in addition, by single-crystal X-ray diffraction studies of three paramagnetic complexes 5, 7 and 8.…”