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)CH₂NPR₃, R = Ph or Cy) differing by the nature of the substituent of the PN phosphorus was explored. Coordination to [RuCl₂(PPh₃)₃] afforded the complexes [RuL^RCl₂(PPh₃)] that were successfully deprotonated at the acidic phosphinomethyl position. With L^Cy, coordination led to a mixture of two isomers. The complexes [RuL^RHCl(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 [RuL^CyHCl(PPh₃)] was thermally stable. Deprotonation of this latter complex was achieved and gave a catalytically competent species for the acceptorless dehydrogenative coupling of alcohols.