Five- and Six-Coordinate Ruthenium(II) Complexes Containing 2-Ph2PC6H4CHNtBu and 2-Ph2PC6H4CH2NHtBu as Chelate Ligands: Synthesis, Characterization, and Catalytic Activity in Transfer Hydrogenation of Ketones

Abstract

Five- and six-coordinate ruthenium(II) complexes containing imino- and aminophosphines have been prepared by ligand exchange processes. Thus, reactions of [RuCl2(PPh3)3] and [RuCl2(DMSO)4] with 2-Ph2PC6H4CHNtBu (a) lead to [RuCl2(κ2-P,N-2-Ph2PC6H4CHNtBu)(PPh3)] (1a) and trans-[RuCl2(κ2-P,N-2-Ph2PC6H4CHNtBu)(DMSO)2] (2a), respectively. Similarly, reactions with 2-Ph2PC6H4CH2NHtBu (b) afford complexes [RuCl2(κ2-P,N-2-Ph2PC6H4CH2NHtBu)(PPh3)] (5b) and [RuCl2(κ2-P,N-2-Ph2PC6H4CH2NHtBu)(DMSO)] (6b) in good yield. The crystal structures of 1a and 5b have been determined by X-ray diffraction. Compound 2a, containing two labile DMSO ligands, has been used as a precursor to synthesize the derivatives [RuCl2(κ2-P,N-2-Ph2PC6H4CHNtBu)L] [L = PPh3 (1a); PPh2Me (3a); PMe2Ph (4a)]. Complexes 1a, 2a, 5b, and 6b are active in catalytic transfer hydrogenation of aryl−alkyl and dialkyl ketones in propan-2-ol. The five-coordinate complexes 1a, 5b, and 6b show higher catalytic activity than the octahedral complex 2a. Complexes 1a and 5b are more efficient catalysts than the precursor complex [RuCl2(PPh3)3]. For the best catalyst, 1a, yields up to 91% were obtained and turnover frequencies may be as high as 41 400 h-1.