Ruthenium complexes featuring cooperative phosphine-pyridine-iminophosphorane (PNN) ligands: synthesis, reactivity and catalytic activity

The coordination to ruthenium(II) centres of two phosphine-pyridine-iminophosphorane ligands L-R (PPh2CH2(C6H3N)CH2N=PR3, R = Ph or Cy) differing by the nature of the substituent of the P=N phosphorus was explored. Coordination to [RuCl2(PPh3)(3)] afforded the complexes [(RuLCl2)-Cl-R(PPh3)] that were successfully deprotonated at the acidic phosphinomethyl position. With L-Cy, coordination led to a mixture of two isomers. The complexes [(RuLHCl)-H-R(PPh3)] were similarly obtained from [RuHCl(PPh3)(3)]. The stability of these complexes depends on the ligand substitution pattern; with L-Ph a CH activation process took place, while [(RuLHCl)-H-Cy(PPh3)] was thermally stable. Deprotonation of this latter complex was achieved and gave a catalytically competent species for the acceptorless dehydrogenative coupling of alcohols.