Photochemical Reaction of Cobalt(II)-Dioxime Macrocyclic Complex in Methanol Solution Containing Tributylphosphine

Abstract

An investigation was made on the photochemical reaction of Co^II(dmgBF₂)₂ (the BF₂ capped species of bis(dimethylglyoxpato)cobalt(II)complex (Co^II(dmgH)₂), Fig.1) in methanot solution containing an excess amount (with the molar ratio of about 2-6: 1) of tributylphosphine (P(n-C₄H₉)₃). The color of the methanol solution, which was purple at temperature higher than -20°C and blue at temperature lower than -40°C, was changed from purple to blue by the irradiation with a low-pressure Hg lamp at room temperature. The visible absorption spectrum of the blue solution was quite similar to that of the blue solution at the temperature lower than -40°C. Therefore, the photoproduct and the low-temperature species of the methanol solution were identified as the same species. The absorption spectrum of the blue solution was also similar to that of Na⁺[Co^I(dmgH)₂.P(n-C₄H₉₃)]^-. Thus, the photoproduct was assigned to H⁺[Co^I(dmkBF₂)₂.P(n-C₄H₉)₃]^-. The photochemical color-change reaction was not observed in benzen or dichloromethane solvent. Therefore, it was proposed that the present photochemical reaction was interpreted by the mechanism in which the central divalent cobalt ion was reduced to the monovalent cobalt ion by methanol.