Transfer hydrogenation reaction using novel ionic liquid based Rh(I) and Ir(III)-phosphinite complexes as catalyst

Abstract

Hydrogen transfer reduction methods are attracting increasing interest from synthetic chemists in view of their operational simplicity. Thus, interaction of [Rh(mu-Cl)(cod)](2) and Ir(eta(5)-C5Me5)(mu-Cl)Cl](2) with phosphinite ligand [(Ph2PO)-C7H11N2Cl]Cl, 1 gave new monodendate (1-chloro-3-(3-methylimidazolidin1-yl)propan-2-yl diphenylphosphinite chloride) (chloro eta(4)-1,5-cyclooctadiene rhodium(I))], 2 and (1chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (dichloro n.5-pentamethylcyclopentadienyl iridium(III))1, 3 complexes, which were characterized by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis. H-1-{P-31}NMR, H-1-C-13 HETCOR or H-1-H-1 COSY correlation experiments were used to confirm the spectral assignments. The novel catalysts were applied to transfer hydrogenation of acetophenone derivatives using 2-propanol as a hydrogen source. The results showed that the corresponding alcohols could be obtained with high activity (up to 99%) under mild conditions. Notably, (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-y1 diphenylphosphinite chloride) (chloro eta(4)-1,5-cyclooctadiene rhodium(I))], 2 complex is much more active than the other analogous complex, 3 in the transfer hydrogenation. Furthermore, compound, 2 acts as excellent catalysts, giving the corresponding alcohols in 97-99% conversions in 5 min (TOF <= 1176 h(-1)). (C) 2016 Elsevier B.V. All rights reserved.