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.