REVERSIBLE COMPLEXATION OF ACETYLENE WITH (PERCHLORATO)COBALT(III) PORPHYRINS TO FORM A NOVEL DICOBALT(II) BIS(PORPHYRIN) WITH A VINYLENE-N,N' LINKAGE

(Perchlorato)cobalt(III) porphyrins bind acetylene reversibly in anhyd rous CH2Cl2. The H-1 NMR and UV-vis spectra of the acetylene adduct at room temperature are characteristic of a Co-II N-substituted porphyri n. The ESR spectra of the acetylene adduct in CH2Cl2 at 4.2 and 77 K s howed signals due to a pi-cation radical and low-spin Co-II. These spe ctroscopic data show that one acetylene combines with two cobalt porph yrins to generate a vinylene-N,N'-linked bis(porphyrin) dicobalt(II) s tructure reversibly via an acetylene pi-complex of Co-II porphyrin pi- cation radical. When coordinating anionic axial ligands (Cl-, SCN-) we re attached, the vinylene-N,N' bis(tetraarylporphyrin) dicobalt(II) co mplexes were stabilized enough to be isolated and fully characterized.