Preparation of monocarbonyl ruthenium complexes bearing bidentate nitrogen and phosphine ligands and their catalytic activity in carbonyl compound reduction

Abstract

Monocarbonyl complexes [RuCl₂(CO)(PR₃)(NN)] (R = Cy, NN = en 1, ampy 2; R = iPr; NN = en 3) have been prepared in a one pot reaction from [RuCl₂(CO)(dmf)(PPh₃)₂], PR₃ and the NN ligand in CH₂Cl₂. Treatment of [Ru(OAc)₂(CO)(PPh₃)₂] with NN ligands in methanol gives the cationic derivatives [Ru(OAc)(CO)(PPh₃)(NN)]OAc (NN = en 4, ampy 5) in which one acetate acts as a bidentate ligand, whereas the other is not coordinated. Diphosphine complexes [RuCl₂(CO)(PP)(PPh₃)] (PP = dppb 6, dppf 7, (R)-BINAP 8, (R,S_p)-Josiphos 9 and (R,R)-Skewphos 10) have been obtained starting from [RuCl₂(CO)(dmf)(PPh₃)₂] and the PP ligand in CHCl₃ or toluene at reflux. The reaction of [Ru(OAc)₂(CO)(PPh₃)₂] with PP in CH₂Cl₂ or toluene affords the fluxional acetate derivatives [Ru(OAc)₂(CO)(PP)] (PP = dppb 11, dppf 12, (R)-BINAP 13, and (R,R)-Skewphos 14). The cationic diphosphine complexes [RuCl(CO)(PP)(en)]Cl (PP = dppb 15, dppf 16) are prepared from [RuCl₂(CO)(dmf)(PPh₃)₂], PP and en in CH₂Cl₂ or, alternatively, from [RuCl₂(CO)₂]_n or the 6, 7 derivatives. Similarly, [Ru(OAc)(CO)(PP)(NN)]OAc (PP = dppb, NN = en 17, ampy 18; PP = dppf, NN = en 19, ampy 20) are isolated starting from [Ru(OAc)₂(CO)(PPh₃)₂], PP and NN ligands or from 11, 12. The derivatives [Ru(OAc)₂(CO)(PP)] show a fluxional behavior in solution as the result of the flexible coordination of acetate ligands. These complexes are found to be active in the transfer hydrogenation and hydrogenation of ketones and aldehydes, including furfural derivatives, at an S/C up to 10 000 and a TOF up to 18 000 h⁻¹.