Rhodium iminophosphine complexes as efficacious oxygen carriers. Crystal structure of a representative dioxygen adduct

Abstract

The synthesis, characterization and reactivity of some square-planar rhodium(I) complexes with new bidentate ligands o-Ph₂PC₆H₄CHNR (R = Et, Prⁿ, Prⁱ or Bu^t) having NP donor atoms have been investigated. Depending on the steric crowding of the ligands the complexes can reversibly form dioxygen adducts, in organic solvent solutions at room temperature. The oxygenation–deoxygenation cycles, which have been monitored by ³¹P NMR spectroscopy, can be repeated several times with minor loss in the starting material. A reversible adduct is similarly obtained by reaction with CO. The reaction of the dioxygen adduct with SO₂ allows the formation of a sulfate derivative. The molecular structure of the dioxygen complex [Rh(o-Ph₂PC₆H₄CHNPrⁱ)₂(O₂)]BPh₄ has been determined by a single-crystal diffraction study: triclinic, space group P, a= 17.450(7), b= 16.518(7), c= 9.624(5)Å, α= 92.79(6), β= 92.52(7), γ= 92.69(7)°, Z= 2, R= 0.057. The co-ordination of the metal may be alternatively described as distorted trigonal bipyramidal or distorted octahedral, according to whether the dioxygen molecule is treated as occupying one or two equatorial sites respectively. The two oxygen atoms, which are equidistant from the metal, are 1.436(9)Å apart.