THE SPECTROSCOPIC PROPERTIES AND ORGANOMETALLIC REACTIVITIES OF COBALT(III) PORPHYRINS

Chlorocobalt(III) porphyrins showed novel UV-vis and H-1 NMR spectra in a non-coordinating solvent to suggest displacement of the cobalt out of the porphyrin plane toward the axial ligand in solution. They underwent insertion of alkynes into the Co-Cl bond to generate sigma-(trans-2-chlorovinyl)cobalt(III) complexes. In a special case, novel [4 + 2]cycloaddition reaction between the Co-N-C(pyrrole-alpha)-C(meso) moiety of [Co(III)Cl(oep)] [oep = octaethylporphyrin dianion] and dimethyl acetylenedicarboxylate took place. The reaction behavior of chlorocobalt(III) porphyrins was compared with that of diaquaperchloratocobalt(III) porphyrins which also reacted with alkynes in the presence of 2,6-lutidine to give analogous sigma-vinylcobalt(III) porphyrins with a 2,6-dimethyl-1-pyridinio substituent occupying the trans-beta-position of the sigma-vinyl group. While the methoxycarbonyl group of methyl propiolate was directed to the alpha side of these sigma-vinylcobalt(III) complexes, the phenyl group of phenylacetylene was found to be directed to the alpha side of sigma-(2-chlorovinyl)cobalt(III) porphyrin and to the beta side of sigma-[2-(2,6-dimethyl-1-pyridinio)vinyl]cobalt(III) porphyrin.