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Photochemistry of Nitrosyl Porphyrins in the Temperature Range 180-300 K and the Effects of Pyridine on Photodenitrosylation of Nitrosyliron Tetraphenylporphyrin
Hoshino, Mikio,Kogure, Mieko
, p. 5478 - 5484 (1989)
Nitrosylmetal tetraphenylporphyrin (NOMTPP, M=Fe,Co, and Mn) in benzene solutions undergoes facile photodenitrosylation to give NO and metal(II) tetraphenylporphyrin, MIITPP.The photodenitrosylation yields of NOFeTPP and NOCoTPP are respectively determined as 0.50 +/- 0.05 and 1.0 +/- 0.05 at both excitation wavelengths 355 and 532 nm.The yield, Φ, in toluene is expressed as a function of temperature: Φ = (1 + 1.56 x 10-2 exp(2400/RT))-1 for NOFeTPP and Φ = (1 + 1.02 x 10-6 exp(5200/RT))-1 for NOCoTPP.Contrary to NOFeTPP and NOCoTPP, the photodenitrosylation yields, Φ, of NOMnTPP are independent of temperature in the range 300-180 K and exhibit excitation wavelength dependence: Φ = 0.78 +/- 0.05 at 355 nm and Φ + 0.62 +/- 0.05 at 532 nm.The effects of the central metal on photodenitrosylation are described.The laser photolysis of NOFeTPP in the presence of low concentration of pyridine revealed that the FeIITPP initially produced reacts with a pyridine molecule, Py, to form five-coordinate (Py)FeIITPP.The five-coordinate (Py)Fe%II%TPP further reacts with Py to give six-coordinate (Py)2FeIITPP, which recombines with NO to regenerate NOFeTPP.The kinetic study has demonstrated that the five-coordinate (Py)FeIITPP which is in equilibrium with (Py)2FeIITPP is responsible for the recombination reaction of (Py)2FeIITPP and NO.
