Mechanistic Insights into Acetophenone Transfer Hydrogenation Catalyzed by Half-Sandwich Ruthenium(II) Complexes Containing 2-(Diphenylphosphanyl)-aniline - A Combined Experimental and Theoretical Study

Several new half-sandwich ruthenium(II) complexes containing 2-(diphenyphosphanyl)aniline (PNH2) of formula {Ru[(kappa P-2,N)PNH2](p-cymene)Cl}Y [Y = Cl (1a), PF6 (1b), BF4 (1c), BPh4 (1d), TfO (1e)] were synthesized and fully characterized both in solution (H-1 NMR and P-31{H-1) NMR spectroscopy) and in the solid state (FTIR, X-ray analysis on single crystal). Complexes 1a and 1b are active precatalysts in the hydrogen transfer reaction of acetophenone, leading to tof values up to 4440h(-1). In comparison, the {Ru[(kappa P-2,N)-PNMe2](p-cymene)Cl}Cl complex leads to a tof value of 100 h(-1) under the same catalytic conditions. The mechanism through which the precatalysts operate was deeply explored by high-resolution MS (ESI) and DFT/PCM studies. The results reveal that the complexes containing PNH2 operate through a bifunctional mechanism analogous to that proposed for diamines and amino alcohol ligands. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)