Stereochemistny and Reactivity of the Complexes with Co-C bond Obtained by Photodecarboxylation

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1. Photodecaiboxylation of the (amino carboxylato)cobalt(III) complexes with glycinate (five-membered) and beta-alaninate (six-membered) chelate ring leads to products having corresponding three- and four-membered chelate ring. The formation of the three-membered Co-CH_2-N ring introduces significant distortions into the octahedral coordination around the Co atom, In the case of photolysis reactions of the mixed-ligand Co(III) complexes containing aminocarboxylates and amines such as phenanthroline (phen) and tris(2-pyridylmethyl)amine (tmpa), the complexes with Co-C bond were isolated. These results are consistent with the idea that most of cobalt(III) complexes with stable Co-C bond have highly unsaturated ligands.2. Photodecarboxylation reaction of the complexes with the S-CH_2-COO five-membered ring provided new complexes with a novel Co-CH_2-S three-membered ring in a good yield. However, the irradiation of UV-light to the complexes containing the S-CHz-CH-COO six-membered ring did not provide analogous complexes with a Co-C bond.3. The complexes with Co-CHz-N and Co-CHz-S three-membered ring are labile in an aquous solution and exist in the equilibrium mixture between their isomers, judging from the ^<13>C-NMR and CD behaviors of these complexes.4. The alpha- and beta-isomers of [Co(eedmp)(phen)]+ (eedmp : N-(2-ethyl)-ethylenediamine-N'-3-propionate), which were obtained by the photodecarboxylation reaction of beta-[Co(eddp)(pben)]+ (eddp : ethylenediamine-N,N'-dipropionate), isomerized to each other in an aqueous solution. The rate constants at 323 K were as follows : k(beta to alpha) = 6.32 x 10^<-6>s^<-1>, k(alpha to beta) 7.23 x 10^7s^<-1>.