RuCl2(DPEphos)(N-N)] (DPEphos = bis[(2-diphenylphosphino)phenyl]ether; N-N = 2-aminomethylpyridine or ethylenediamine): synthesis, characterization and transfer hydrogenation of aryl-ketones

Abstract

The complexes trans/cis-[RuCl2(DPEphos)(ampy)] (trans – 1a; cis – 1b) and trans/cis-[RuCl2(DPEphos)(en)] (trans – 2a; cis – 2b) were obtained from the reactions of mer-[RuCl2(DPEphos)(PPh3)] (PPh3 = triphenylphosphine) with the corresponding amine in CH2Cl2. The isomer 1a was observed in situ when the reaction was carried out at r.t.; isolation leads to mixtures with 1b, while the latter was isolated when the reaction was performed under reflux. On the other hand, trans-[RuCl2(DPEphos)(en)] (2a) was obtained at r.t., in good yield and the cis-isomer 2b was observed when the reaction was carried out under reflux or when a CH2Cl2 solution of 2a is exposed to ambient light, but 2b was not isolated in pure form even under reflux for one week. Cyclic voltammetry studies revealed the presence of one reversible process with E1/2 0.57 and 0.40 V for 1b and 2a, respectively. Both 1b and 2a were used as pre-catalysts for reduction of acetophenone and p-substituted acetophenones (F–, Me– and MeO–) in transfer-hydrogenation conditions (isopropanol, 82 °C, and pre-catalyst:KOH:acetophenones in molar ratio 1:20:500 and/or 1:20:1000) showing conversions of 93–99% and TOF values up to 4.2 104 h−1.