Ruthenium(II) carbonyl complexes of P,P and P,O donor diphosphine ligands, Ph₂P(CH₂)_nPPh₂ and Ph₂P(CH₂)_nP(O)Ph₂, n = 2, 3 and their activities in catalytic transfer hydrogenation reactions

Abstract

The polymeric precursor [RuCl2(CO)2]n reacts with the ligands, P∩P (a, b) and P∩O (c, d), in 1:1 M ratio to generate six-coordinate complexes [RuCl2(CO)2(ƞ2-P∩P)] (1a, 1b) and [RuCl2(CO)2(ƞ2-P∩O)] (1c, 1d), where P∩P: Ph2P(CH2)nPPh2, n = 2(a), 3(b); P∩O: Ph2P(CH2)nP(O)Ph2, n = 2(c), 3(d). The complexes are characterized by elemental analyses, mass spectrometry, thermal studies, IR, and NMR spectroscopy. 1a–1d are active in catalyzed transfer hydrogenation of acetophenone and its derivatives to corresponding alcohols with turnover frequency (TOF) of 75–290 h−1. The complexes exhibit higher yield of hydrogenation products than catalyzed by RuCl3 itself. Among 1a–1d, the Ru(II) complexes of bidentate phosphine (1a, 1b) show higher efficiency than their monoxide analogs (1c, 1d). However, the recycling experiments with the catalysts for hydrogenation of 4-nitroacetophenone exhibit a different trend in which the catalytic activities of 1a, 1b, and 1d decrease considerably, while 1c shows similar activity during the second run.