Cis-influence of hydroporphyrin macrocycles on axial ligation equilibria and alkyl exchange reactions of alkylcobalt(III) porphyrin complexes.
Cis-influence of hydroporphyrin macrocycles on axial ligation equilibria and alkyl exchange reactions of alkylcobalt(III) porphyrin complexes.
复制标题
氢卟啉大环对烷基钴(III)卟啉配合物的轴向连接平衡和烷基交换反应的顺式影响。
DOI：
10.1021/ic991304t
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发表时间：
2000
影响因子：
4.6
通讯作者：
Summers,JS
中科院分区：
文献类型：
--
作者：
Stolzenberg,AM;Summers,JS
报道了吡啶和取代吡啶在甲苯溶液中与辛基卟啉（OEP）、辛基乙基氯（OEC）和辛基乙基异菌氯（OEiBC）的烷基钴（III）配合物的稳定性常数。稳定性常数与含氮配体的碱强度有关。观察到大环饱和水平对稳定性常数的顺式影响。给定的吡啶配体与烷基钴（III）配合物的配位稳定常数大约比相应的钴（II）配合物的稳定常数小10倍。热力学循环的分析表明，这导致配合物的稳定性下降，相对于Co - C键的均裂配位，“基础”效应。不同四吡咯的钴配合物之间发生烷基交换。平衡数据表明，交换是非统计性的，并且通过增加四吡咯大环的饱和度来稳定Co - C键。
Stability constants are reported for the coordination of pyridine and substituted pyridines to the alkylcobalt(III) complexes of octaethylporphyrin (OEP),t-octaethylchlorin (OEC), andttt-octaethylisobacteriochlorin (OEiBC) in toluene solution. The stability constants correlate with the base strength of the nitrogenous ligand. A cis-influence of the macrocycle saturation level on the stability constants is observed. Stability constants for coordination of a given pyridine ligand to an alkylcobalt(III) complex are roughly 10 times smaller than the stability constants for the corresponding cobalt(II) complex. Analysis of a thermodynamic cycle demonstrates that this leads to decreased stability of the complex with respect to Co−C bond homolysis upon ligand coordination, a “base-on” effect. Alkyl exchange occurs between cobalt complexes of different tetrapyrroles. Equilibrium data establish that the exchange is nonstatistical and that the Co−C bond is stabilized by increasing the saturation of the tetrapyrrole macrocycle.