氯化原卟啉Ⅸ二甲酯合钴（Ⅲ）的合成及其与咪唑反应动力学的研究

SYNTHESIS OF Co(Ⅲ) PP ⅨDMECI AND KINETIC STUDY OF THE REACTION OF Co(Ⅲ)PPⅨDMECI WITH IMIDAZOLES

从原卟啉Ⅸ（ＰＰⅨ）出发合成氯化原卟啉Ⅸ二甲酯合钴（Ⅲ）．分别用元素分析、ＵＶ光谱和ＩＲ光谱表征．２９８Ｋ时，测定氯化原卟啉Ⅸ二甲酯合钴（Ⅲ）与咪唑反应在丙酮或二氯甲烷溶剂中的表观速率常数ｋｏｂｓ，结果表明反应的决速步是单分子咪唑中间体Ｃｏ（Ⅲ）ＰＰⅨＤＭＥ（ＲＩｍ）Ｃｌ中氯的离解。总反应速率方程对咪唑是一级反应；氯离解的速率常数ｋ１依赖于溶剂与氯形成氢键的能力，即＂远位咪唑氢键效应＂；当咪唑中出现２－甲基、２－苯基时，由于取代基与卟啉配位体之间的相互作用，促使反应氯的离解速率增加，产生＂近位张力效应＂．

Protoporphyrin Ⅸ dimethyl ester complex of cobalt(Co(Ⅲ)PPⅨDMECl) was synthesized from protoporphyrin Ⅸ(PPⅨ) and characterized by elemental analysis, UV spectrum, IR spectrum and melting point respectively. The observed rate constants(kobs) of the reactions of Co(Ⅲ←)PPⅨ DMECl with imidazoles (RIm) have been investigated in acetone and dichloromethane solvents at 298. 15K. Experiments show that the rate-determining step is chloride ionization from the mono(imidazole) intermediate. The rate law for the overall reaction is the first order in imidazole. The chloride ionization rate constant(k1) strongly depends on the avility of solvent to form hydrogen-bonding, i. c. “distal-imidazole hydrogen bond effect”.When a 2-methyl or 2-phenyl substituent is present the steric strain with porphyrin ligand increases the rate of the trans cholride ionization, i. e.“proximal-strain effect”.