Photochemical and thermal disproportionation of [(CO) 4CoM(CO) 3(LL)] (M  Mn, Re; LL = 2,2′-bipyridine, 2-pyridinecarbaldehyde N-isopropylimine) complexes

Abstract

A study has been made of the secondary thermal reactions occurring after MLCT photolysis of [(CO) 4CoRe(CO) 3(LL)] (LL = 2,2′-bipyridine, 2-pyridinecarbaldehyde N-isopropylimine). Contact ion pairs {[Re(CO) 3(LL)] +[Co(CO) 4 −1]} have been detected as final products upon irradiation into the MLCT band of the Re complexes in toluene. The initial quantum yield of the 476.5 nm photolysis of the 2,2′-bipyridine complex in toluene at 223 K is independent of the concentration and light intensity, implying that the contact ion pairs are formed by radical-radical interaction without involvement of any other donor molecule. The quantum yields increase with temperature. At initial concentrations of 10 −2 mol 1 −1 with toluene as the solvent the photodisproportionation into contact ion pairs is strongly retarded at about 50% conversion; this effect seems to depend on the concentration of the contact ion pair. Tle complexes under study disproportionate thermally into ion pairs when their solutions in CH 3CN or THF are left in the dark. In 2-MeTHF at T ⩽ 243 K only [(CO) 4CoMn(CO) 3(2,2′-bipyridine)] undergoes disproportionation.