Photochemical studies of Co2(CO)6(acetylene) complexes and their phosphine derivatives in frozen Nujol matrices

Photolysis of Co-2(CO)(6)(alkyne), where alkyne = H2C2 (I), (C2H5)(2)C-2 (II) (C6H5)(2)C-2 (III) and C6H5C2H (IV) in frozen Nujol at ca. 90 K results in loss of CO to give Co-2(CO)(5)(alkyne) in which GO-loss appears to be from the axial position. Complete conversion to a second isomer, presumed to have a vacancy in an equatorial position, or to starting material is observed for all compounds upon annealing the matrices to ca. 140 K. The second isomer is also formed by Co-2(CO)(5)[(C6H5)(2)C-2] upon photolysis at lambda < 280 nm. Photolysis of Co-2(CO)(6)As-2 (V), gave photochemical and annealing products whose spectra were analogous to those of the alkyne compounds. Photolysis of phosphine substituted derivatives such as axiaE-Co-2(CO)(5)(PR3)(C2R2'), where R = Bu; R' = H (VI), R' = H; R' = H (VII), R = OPh, R' = H (VIII), R = Ph; R' = Ph (M) yields two isomeric CO-loss products. Annealing samples of V-IX to ca. 140 K results in simple reaction reversal. Solution photolysis of M with PPh3 gives Co-2(CO)(4)(PPh3)(2)(Ph2C2). Photolysis of Co-2(CO)(4)(PPh3)(2)(H2C2) (X) yields two products. Annealing the sample reforms the starting material and also generates a new species. Photolysis of Co-2(CO)(4)(Ph2P)(2)CH2][(C2H5)(2)C-2] (XI) forms a single product that reforms XI upon annealing. (C) 2000 Published by Elsevier Science S.A. All rights reserved.