Activation and transfer of O2 to organic electrophiles by [RuH(dcpe)2]+
Abstract
The crystal structure of the 16-electron hydride [RuH(dcpe)2]PF6 (1·PF6) [dcpe=1,2-bis(dicyclohexylphosphino)- ethane] shows a short contact between Ru and a cyclohexyl CH2, which was not observed in the disordered tetraphenylborate 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 hydrido dioxygen complex [RuH(η2-O2)(dcpe)2]+ (4), formed by reaction of 1 with O2, does not react with nucleophiles such as olefins and PPh3, but does show 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 dioxygen complex of a late transition metal, as the O2-activating complex 1 is partially regenerated upon oxygen transfer from 4 to the substrate. All these reactions show that oxygen transfer from 4 to an organic substrate effectively competes with oxidation of the dcpe ligand.