Synthesis and characterisation of cyclometallated orthoazobenzene complexes of Ru(II): crystal and molecular structure of [RuCl(CO)(η2-C,N-C6H4NNPh)(PPh3)2]·0.5CHCl3·0.5Et2O. Is there a similarity to the hydroxyazo/ketohydrazone tautomerisation in ortho-

Treatment of [RuHCl(CO)(PPh3)3] with Hg(o-C6H4NNC6H5)2 affords [RuCl(CO)(η2-C,N-o-C6H4NNC6H5)(PPh3)2] (1) in good yield, where the cyclometallated azobenzene ligand coordinates through an ortho-C and N to give a five-membered chelate ring. Reaction of 1 with AgNO3, followed by NaBr or NaI, affords the chloride exchanged products [RuX(CO)(η2-C,N-o-C6H4NNC6H5)(PPh3)2] (2 and 3), while reaction of 1 with AgOC(O)Me gives the monondentate acetate complex [Ru{η1-OC(O)Me}(CO)(η2-C,N-o-C6H4NNC6H5)(PPh3)2] (4), and reaction with NaS2CNEt2·2H2O gives the chelate complex [Ru(CO)(S2CNEt2)(η2-C,N-o-C6H4NNC6H5)(PPh3)] (5). The cationic complex [Ru (CO)(bipy)(η2-C,N-o-C6H4NNC6H5)(PPh3)][BF4] (6) is obtained on treatment of 1 with AgNO3, followed by bipy and NaBF4. In the solid-state structure of 1, significant changes in the bond lengths for the cyclometallated azobenzene ligand are observed and are discussed with the aid of a range of related examples, and compared with those observed in the well-known hydroxyazo/ketohydrazone tautomeric process in azodyes.