The Spectroscopic Properties and Organometallic Reactivities of Cobalt(III) Porphyrins

Chlorocobalt(III) porphyrins showed novel UV-vis and 1H 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 σ-(trans-2-chlorovinyl)cobalt(III) complexes. In a special case, novel [4+2]cycloaddition reaction between the Co–N–C(pyrrole-α)-C(meso) moiety of [CoIIICl(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 σ-vinylcobalt(III) porphyrins with a 2,6-dimethyl-1-pyridinio substituent occupying the trans-β-position of the σ-vinyl group. While the methoxycarbonyl group of methyl propiolate was directed to the α side of these σ-vinylcobalt(III) complexes, the phenyl group of phenylacetylene was found to be directed to the α side of σ-(2-chlorovinyl)cobalt(III) porphyrin and to the β side of σ-[2-(2,6-dimethyl-1-pyridinio)vinyl]cobalt(III) porphyrin.