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

Cationic ruthenium pincer complexes, [Ru(CNC)(CO)(PPh 3 )Cl]X (CNC = 2,6‐bis(1‐methylimidazol‐2‐ylidene)‐pyridine, X = Cl − [ 1a ], PF 6 − [ 1b ]), [Ru(CNC)(PPh 3 ) 2 Cl]X (X = Cl − [ 2a ], PF 6 − [ 2b ]) and [Ru(CNC)(PPh 3 ) 2 (H)]X (X = Cl − [ 3a ], PF 6 − [ 3b ]) with triphenylphosphine, CO and halides as coligands have been synthesised and characterised by 1 H, 13 C, 31 P 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.