Reactivity of Five-Coordinate Intermediate Generated by Laser Photolysis of Monoligated Chloro(5,10,15,20-tetraphenylporphinato)chromium(III) in Toluene

Article abstract of DOI:10.1246/bcsj.68.2293

The Cr(III) porphyrin complexes (1) and <(Cr(tpp)(Cl)(py)> (2) (tpp represents the dianion of 5,10,15,20-tetraphenylporphine) crystallized from a chloroform-toluene mixture in the tetragonal space group I4, Z = 2, a = 13.559(5), b = 13.559(5), c = 9.770(3) Angstroem, V = 1796(3) Angstroem³, and from a dichloroethane-toluene mixture containing a small amount of pyridine (py) in the monoclinic space group P2₁/n, Z = 4, a = 14.655(5), b = 23.498(4), c = 13.152(2) Angstroem, β = 101.54(1) deg, V = 4437(2) Angstroem³, respectively.The axial Cr-O bond length for 1 and the axial Cr-N bond length for 2 are 2.239(3) and 2.140(5) Angstroem, respectively.Laser irradiation of the toluene solution of causes the photodissociation of the axial ligand L, where L represents H2O or 3-cyanopyridine, to give the five-coordinate intermediate .The rate constant of the axial ligand recombination reaction falls into a narrow range around 1x10⁹ mol^-1 kg s^-1 at 25.0 deg C for both reactions.The activation parameters indicate the very high reactivity of the five-coordinate intermediate.The diffusion-controlled process is regarded as a rate-determining step for the recombination.