Dioxygen Binding to a Cobalt(II) Porphycene Complex and Its Auto-Oxidized Cobalt(III) Complex

摘要

The reaction between a cobalt porphycene complex,[Co~(II)(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 [Co~(III)-O_2~(-centre dot)].In the presence of pyridine as an axial ligand,the formation of a six-coordinated superoxide 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.nu(Co-O_2) stretching is also observed at 540 cm~(-1).The nu(O-O) and nu(Co-O_2) wavenumbers in the complex were assigned by means of ~(18)O_2 substitution.nu(Co-O_2) of the O_2 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 Co~(III) complex,which was structurally determined by X-ray analysis.The complex crystallized in the monoclinic space group P2_1,a = 9.6266(4) A,b = 12.6343(5) A,c = 15.6566(6) A,beta = 99.1200(10)deg,V = 1880.17(13) A~3,and Z = 2.The Co~(III) ion lies on the plane of the porphycenato core,and coordinates four porphycenato nitrogen atoms and two pyridine nitrogen atoms.The complex cation,[Co~(III)(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.