Laser Flash Photolysis Studies of Nitritomanganese(III) Tetraphenylporphyrin. Reactions of O2, NO, and Pyridine with Manganese(II) Tetraphenylporphyrin

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• 作者：Mikio Hoshino ; Yutaka Nagashima ; Hiroshi Seki ; Malcolm De Leo ; and Peter C. Ford
• 刊名：Inorganic Chemistry
• 出版年：1998
• 出版时间：May 18, 1998
• 年：1998
• 卷：37
• 期：10
• 页码：2464 - 2469
• 全文大小：128K
• 年卷期：v.37,no.10(May 18, 1998)
• ISSN：1520-510X

文摘

Laser photolysis of nitritomanganese(III)tetraphenylporphyrin, Mn^IIITPP(ONO)(1), in degassed toluene givesmanganese(II) tetraphenylporphyrin, Mn^IITPP(2), plus NO₂. The quantum yield, , forthe formation of Mn^IITPP is dependent on the excitation wavelength: = 0.045 at 355 nmand = 0.0064 at 532 nm. Continuousphotolysis studies reveal that the quantum yield for the netphotodecomposition of 1 is much smaller(10^-4).Thus, Mn^IITPP produced by laser photolysis ofMn^IIITPP(ONO) mostly returns to 1 byrecombination with NO₂according to second-order kinetics with a rate constant 2.2 ×10⁹ M^-1s^-1. The kinetics for the reactionsofMn^IITPP with O₂, NO, and pyridine wereinvestigated in detail. In aerated toluene,Mn^IITPP reversibly reactswith oxygen to yield the dioxygen adduct, MnTPP(O₂)(3). The rate constants,k_f(O₂) andk_b(O₂), for theformationand dissociation of 3 at 300 K were determined to be 1.93× 10⁷ M^-1s^-1 and 9.0 × 10⁴s^-1, respectively, andthe equilibrium constant,k_f(O₂)/k_b(O₂),is therefore 2.1 × 10² M^-1.Mn^IITPP reacts with pyridine to giveMn^IITPP(Py) with a rate constant of 9.5 × 10⁸M^-1 s^-1.Mn^IITPP reacts with NO to yield nitrosylmanganeseporphyrin,Mn^IITPP(NO), with the rate constant 5.3 ×10⁸ M^-1s^-1. The association reactions ofMn^IITPP with NO, pyridine,O₂, and NO₂ are discussed in comparison withthose of other metalloporphyrins.