Orzeł Lukasz, Fiedor Leszek, Wolak Maria, Kania Agnieszka, van Eldik Rudi, Stochel Grazyna
Inorganic Chemistry, Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany.
Chemistry. 2008;14(30):9419-30. doi: 10.1002/chem.200800991.
The mechanism of acetate-assisted transmetalation of tetrapyrroles was investigated in a model system consisting of chlorophyll a and copper(II) acetate in organic solvents by using a spectroscopic and kinetic approach. Surprisingly, acetate ions bind to the central Mg in chlorophyll much more strongly than do acetonitrile, methanol and even pyridine, one of the best ligands in chlorophyllic systems. This exceptionally strong non-symmetrical axial ligation of the central Mg by acetate causes its out-of-plane displacement and deformation of the tetrapyrrole ring, thus facilitating the interaction with an incoming CuII complex. This mechanism is controlled by a keto-enol tautomerism of the chlorophyll isocyclic ring. Additionally, depending on solvent, acetate activates the incoming metal ions. These new insights allow to suggest a mechanism for the acetate method of metal exchange in tetrapyrrolic macrocycles, which resembles biological insertion of metal ions into porphyrins. It also provides a guideline for the design of more efficient methods for the metalation of porphyrins and related macrocycles.
通过光谱和动力学方法，在由叶绿素a和醋酸铜（II）组成的有机溶剂模型体系中，研究了醋酸根辅助的四吡咯跨金属化机理。令人惊讶的是，醋酸根离子与叶绿素中心镁的结合比乙腈、甲醇甚至吡啶（叶绿素体系中最佳配体之一）都要强得多。醋酸根对中心镁这种异常强的非对称轴向配位导致其平面外位移和四吡咯环变形，从而促进与进入的CuII配合物的相互作用。该机理受叶绿素异环的酮-烯醇互变异构控制。此外，根据溶剂不同，醋酸根会活化进入的金属离子。这些新见解有助于提出四吡咯大环中醋酸根法金属交换的机理，该机理类似于金属离子在卟啉中的生物插入。它还为设计更有效的卟啉及相关大环金属化方法提供了指导。
