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

Abstract Several new half‐sandwich ruthenium(II) complexes containing 2‐(diphenyphosphanyl)aniline (PNH2) of formula {Ru[(κ2P,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 (1H NMR and 31P{1H} 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 4440 h–1. In comparison, the {Ru[(κ2P,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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)