Ligand controlled dioxygen oxidation of rhenium nitrosyl complexes

Abstract

The addition of an excess of phenyldiazomethane to chlorobenzene solutions of the cationic dinitrosyl bisphosphine rhenium(−I) complexes [Re(NO)₂(PR₃)₂][BAr^F₄] (R = Cy 1a, R = ⁱPr 1b) gave the corresponding benzylidene complexes [Re{CH(C₆H₅)}(NO)₂(PR₃)₂][BAr^F₄] (2a and 2b) in good yields. The treatment of 2b with dioxygen resulted in the oxidation of one of the nitrosyl ligands into the corresponding η²-nitrito (3b) and nitrato complexes (4b) both in the solid state and in solution. In the case of the tricyclohexylphosphine derivative 2a the analogous conversion was not observed. A mechanism for the reaction of 2b with O₂ is proposed which is based on an initial SET to the O₂ molecule and subsequent formation of a peroxynitrite complex followed by the formation of a dinuclear µ-N₂O₄ intermediate. This in turn would undergo fission of the peroxo bond to afford 3b. A related sequence of steps is anticipated for the transformation of 3b to 4b. Furthermore, a similar mechanism seems reasonable for the seemingly topochemical reaction of 2b to 3b and 4b in the solid state. The initial SET to dioxygen and subsequent formation of the peroxynitrite complex is supported by DFT calculations on the trimethylphosphine model complexes [Re(CH{C₆H₅})(NO)₂(PMe₃)₂]ⁿ⁺ (n = 1 and 2).