Coordination and Catalytic Activity of Ruthenium Complexes Containing Tridentate P,N,O Ligands

The coordination chemistry of RuII ions with [2-(diphenylphosphanyl)-N-(o-hydroxybenzylidene)]aniline (PNO-H) and the methylated analogue PNO-Me have been studied. Thus, [(PNO)RuCl(dmso)2] (1), [(PNO)2Ru] (2), [(PNO)RuCl(PPh3)] (3) and [(PNO)RuCl(CO)2] (4) were synthesized by reactions of various RuII precursors with PNO-H. Treatment of PNO-Me with [RuCl2(dmso)4] resulted in in the formation of [P,N-(PNO-Me)Ru(dmso)2Cl2] (5). However, complexation of PNO-Me with [RuCl2(CO)3(THF)] (THF = tetrahydrofuran) provided a mixture of [P,N-(PNO-Me)Ru(CO)2Cl2] (6) and 4 because O-demethylation took place during the reaction. All of the RuII complexes have been characterized by elemental analysis and spectroscopic techniques, as well as X-ray crystal structural analysis for 2, 4 and 6. The ruthenium complexes investigated in this work, except 2, are good precatalysts for the reductive amination of amine with alcohols, and 4 appears to be the best. Moreover, 4 can catalyze the direct amination of nitrobenzene with benzyl alcohol to the corresponding secondary amine.