Dioxygen binding to a cobalt (II) porphycene complex and its auto-oxidized cobalt (III) complex

The reaction between a cobalt porphycene complex, [CoII(TPrPc)] (TPrPc is a dianion of 2, 7, 12, 17-tetrapropylpor-phycene), and dioxygen was investigated by means of UV-vis, ESR, and resonance Raman (RR) spectroscopies. These spectra indicate the formation of [CoIII-O2-·]. In the presence of pyridine as an axial ligand, the formation of a six-co-ordinated superoxides species was confirmed by its characteristic ESR spectrum. The six-coordinated dioxygen adduct exhibits an RR band at 1144 cm-1, which is characteristic of O-O stretching of superoxide. ν(Co-O2) stretching is also observed at 540 cm-1. The ν(O-O) and ν(Co-O2) wavenumbers in the complex were assigned by means of 18O2 substitution. ν(Co-O2) of the O2 adduct shows a higher frequency relative to those of cobalt porphyrin complexes. On standing for one day at room temperature, the compound was auto-oxidized to a CoIII complex, which was structurally determined by X-ray analysis. The complex crystallized in the monoclinic space group P21/n, a=9.6266(4) A, b=12.6343(5) A, c=15.6566(6) A, β=99.1200(10)deg, V=1880.17(13) A3, and Z=2. The CoIII ion lies on the plane of the porphycenato core, and coordinates four porphycenato nitrogen atoms and two pyridine nitrogen atoms. The complex cation, [CoIII(TPrPc)(Py)2]+, exhibits a slightly distorted octahedral coordination geometry. The average Co-N (porphycenato pyrrole) distance and the Co-N (pyridine) distance are 1.929 and 1.952 A, respectively. (author)