Reversible Complexation of Acetylene with (Perchlorato)cobalt(III) Porphyrins To Form a Novel Dicobalt(II) Bis(porphyrin) with a Vinylene-N,N‘ Linkage

Abstract

(Perchlorato)cobalt(III) porphyrins bind acetylene reversibly in anhydrous CH2Cl2. The 1H NMR and UV−vis spectra of the acetylene adduct at room temperature are characteristic of a CoII N-substituted porphyrin. The ESR spectra of the acetylene adduct in CH2Cl2 at 4.2 and 77 K showed signals due to a π-cation radical and low-spin CoII. These spectroscopic data show that one acetylene combines with two cobalt porphyrins to generate a vinylene-N,N‘-linked bis(porphyrin) dicobalt(II) structure reversibly via an acetylene π-complex of CoII porphyrin π-cation radical. When coordinating anionic axial ligands (Cl-, SCN-) were attached, the vinylene-N,N‘ bis(tetraarylporphyrin) dicobalt(II) complexes were stabilized enough to be isolated and fully characterized.