Diastereomeric half-sandwich Ru(II) cationic complexes containing amino amide ligands. Synthesis, solution properties, crystal structure and catalytic activity in transfer hydrogenation of acetophenone

The cationic complexes [(eta(6)-arene) Ru(N,O-amino amide) X]Y (arene = p-cymene or indane; N, O-amino amide = (L)-proline amide or (L)-phenylalanine amide; X = Cl or I; Y = Cl, I or PF6) have been synthesised and fully characterized by spectroscopic and analytical methods. In several cases (1a, 3a, 4a, 4b, 5) the metal configuration has been definitively established by X-ray analysis on single crystal. The lability of the metal center in solution has been studied by H-1 NMR and CD techniques. The highest configurational stability has been found in the complexes of the type [(eta(6)-indane)Ru(N,O-proline amide)Cl]Y (4a, b). The complexes 1b, 2a-b, 3b, 4b and 5 are good precatalysts for the transfer hydrogenation of acetophenone in basic i-PrOH, with ee up to 76% at 30 degrees C. An ESI(+)-MS study of pre-catalytic solutions has provided useful information on the catalytic mechanism. (C) 2009 Elsevier B. V. All rights reserved.