Activation and transfer of O-2 to organic electrophiles by [RuH(dcpe)(2)](+)

The crystal structure of the 16-electron hydride [RuH(dcpe)(2)]PF6, (1 . PF 6) [dcpe = 1,2-bis(dicyclohexylphosphino)ethane] shows a short contact betw een Ru and a cyclohexyl CH2,which was not observed in the disordered tetrap henylborate salt [RuH(dcpe)(2)]BPh4 (1 . BPh4). The comparison of the X-ray structure of 1 . PF6 with those of [RuCl(dcpe)(2)]PF6 (2) and trans-[RuCl2 (dcpe)(2)] (3) indicates that electronic effects co-operate with the steric ones in the stabilization of these 16-electron species. The hydride dioxyg en complex [RuH(eta(2)-O-2)(dcpe)(2)](+) (4), formed by reaction of 1 with O-2, does not react with nucleophiles such as olefins and PPh3, but does sh ow nucleophilic properties, reacting with activated olefins (TCNE, 2-methyl -1,4-naphthoquinone) and with carbonyl compounds [heptanal, PhC(O)Cl]. The reaction of 4 with heptanal shows an unprecedented reaction mode for a diox ygen complex of a late transition metal, as the O-2-activating complex 1 is partially regenerated upon oxygen transfer from 4 to the substrate. All th ese reactions show that oxygen transfer from 4 to an organic substrate effe ctively competes with oxidation of the dcpe ligand.