EPR Study of Photochemical Reactions of fac- and mer-[Cr(CO)3(η1-L2)(η2-L2)]+ (L2 = Bidentate Phosphine, Arsine, or Phosphonite Ligand)

Abstract

Rearrangement of fac-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + to mer-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + (L 2 is a bidentate phosphine or arsine ligand) is a rapid thermally activated process. Loss of CO from mer-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + to form trans-[Cr(CO) 2 (η 2 -L 2 ) 2 ] + is shown to be a clean photochemical process, perhaps the first example of a quantitative photochemical transformation for a Cr(I) complex. The bidentate phosphonite ligand, L 2 = (MeO) 2 PCH 2 CH 2 P(OMe) 2 , behaves quite differently: fac-[Cr(CO) 3 (η 2 -L 2 )(η 1 -L 2 )] + undergoes photochemical loss of CO to form a five-coordinate complex which converts slowly via thermal activation to trans-[Cr(CO) 2 (η 2 -L 2 ) 2 ] + .