Cationic ruthenium(II)–NHC pincer complexes: Synthesis, characterisation and catalytic activity for transfer hydrogenation of ketones

Abstract

Cationic ruthenium pincer complexes, [Ru(CNC)(CO)(PPh3)Cl]X (CNC = 2,6‐bis(1‐methylimidazol‐2‐ylidene)‐pyridine, X = Cl− [1a], PF6− [1b]), [Ru(CNC)(PPh3)2Cl]X (X = Cl− [2a], PF6− [2b]) and [Ru(CNC)(PPh3)2(H)]X (X = Cl− [3a], PF6− [3b]) with triphenylphosphine, CO and halides as coligands have been synthesised and characterised by 1H, 13C, 31P NMR, mass and single‐crystal X‐ray crystallography. The application of Ru complexes in the transfer hydrogenation of a wide range of ketones with 2‐propanol as the hydrogen source is explored. The in situ transformations observed during the synthesis help understand and suggest a plausible mechanism via the hydride complex 3b. All complexes appear to be efficient catalyst precursors for transfer hydrogenation of ketones.