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(μ-Cl)(cod)]2 and Ir(η5-C5Me5)(μ-Cl)Cl]2 with phosphinite ligand [(Ph2PO)-C7H11N2Cl]Cl, 1 gave new monodendate (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (chloro ɳ4-1,5-cyclooctadiene rhodium(I))], 2 and (1-chloro-3-(3-methylimidazolidin-1-yl)propan-2-yl diphenylphosphinite chloride) (dichloro ɳ5-pentamethylcyclopentadienyl iridium(III))], 3 complexes, which were characterized by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis. 1H-{31P} NMR, 1H-13C HETCOR or 1H-1H 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-yl diphenylphosphinite chloride) (chloro ɳ4-1,5-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).