Reactivity of Group 6 cationic complexes. Part 5. Photochemical water reduction by a chromium(II) metallorganic system and X-ray crystal and molecular structure of cis- and trans-[Cr(CO)2(η-C5Me5){P(OMe)3}2]+

Abstract

Laser irradiation at 488 nm of a methanol solution of [Mo(CO)₃(η-C₅Me₅){P(OMe)₃}]BF₄(1) gives [Mo(CO)₂(η-C₅Me₅){P(OMe)₃}(MeOH)]BF₄(2), as a mixture of cis and trans isomers. Irradiation at 458 nm of methylene chloride or methanol solutions of the corresponding chromium derivative [Cr(CO)₃(η-C₅Me₅){P(OMe)₃}] BF₄(4) gives a mixture of cis and trans-[Cr(CO)₂(η-C₅Me₅){P(OMe)₃}₂]BF₄(5), together with unidentified products. The solid-state structures of both cis-and trans-(5) were determined by single-crystal X-ray diffraction. The structural models were refined to R= 0.078, (R′= 0.080) for 770 independent reflections [cis-(5)] and to R= 0.046 (R′= 0.049) for 2 439 independent reflections [trans-(5)]. Crystal data: cis-(5), orthorhombic, space group Pbca, a= 17.738(5), b= 26.370(6), c= 11.344(7)Åtrans-(5), monoclinic, space group I2/a, a= 16.167(5), b= 19.814(6), c= 16.106(2)Å, β= 90.20(2)°. Complex (5) photochemically reduces water, being transformed into the chromium(III) cluster [Cr₄(µ-OH)₆(η-C₅Me₅)₄][BF₄]₂(6). Quantum-yield data are reported for this process.