钴(II)卟啉与咪唑类配体配位反应热力学、动力学

钴（Ⅱ）卟啉能可逆地结合氧而作为血红蛋白的模拟化合物．此外,维生素B12的某些辅酶反应是通过Co（Ⅱ）自由基中间物进行的,而Co（Ⅱ）卟啉的d7Co（Ⅱ）离子在dz2轨道的单个未配对电子使其具有自由基性质,所以人们对钴（Ⅱ）卟啉表示了极大的兴趣[1-5].Walker的早期工作[1]

Thermodynamics and Kinetics of Coordination Reaction of Imidazolates with Cobalt(II) Porphyrin

The thermodyntamics of axial coordination reaction of Cobalt(Ⅱ)(p-OCH3)TPP with various ligands [L=Im(imidazole), MeIm (2-methydrimidazole), EMIm (2-ethyl-4-methylimidazole)] at different temperatures in dichloromethane solvent have been studied.
Cobalt(Ⅱ)(p-OCH3)TPP+nL↔ Cobalt(Ⅱ)(p-OCH3)TPP﹒Ln
The equilibrium constant (β) and stoichiometric number (n) of reaction (1) were measured by means of Shimadzu UV-240 spectrophotometer. The changes of standard molar enthalpy △ rHm? and molar entropy △rSm? of reaction (1) were calculated. The steric and electronic effects of the three axial ligands on the reaction were compared.
The kinetic study for the axial coordination faster reaction of Cobalt(Ⅱ) (p-OCH3)TPP with Im in dichloromethane at different temperatures by means of a Union Giken RA-401 stopped-flow spectrophotometer was reported. The mechanism of reaction (1) was postulated as follows:
Co(Ⅱ)(p-OCH3) TPP+ Im↔ Co(Ⅱ)(p-OCH3) TPP﹒Im
Co(Ⅱ)(p-OCH3) TPP﹒Im+Im→Co(Ⅱ)(p-OCH3) TPP﹒(Im)2
The parameters K and k were evaluated. The △ rHm?, △rSm? of a pre-equilibrium step (2) and △r≠Hm, △r≠Sm of a rate-determining step (3) were also calculated.