Oxotungsten(V) and (VI) complexes of 1,3-dimethyllumazine as models for the tungstopterin cofactor
作者:Fridmann M. Hornung、Wolfgang Kaim
DOI:10.1039/ft9949002909
日期:——
The coordination of W(O)Cl3 or W(O)2Cl2 to 1,3-dimethyllumazine (DML) occurs at the O(4) and N(5) centres of the chelating DML. While the colourless dioxotungsten(VI) complex shows only partially reversible reduction behaviour, the oxidizable red monooxotungsten(V) complex is stable and could be studied by EPR, UV–VIS, IR and NMR spectroscopy. These latter techniques have been used to confirm the coordination site via changes in the carbonyl stretching bands and via paramagnetic shifts of the proton resonances. Although the EPR results of (L)W(O)Cl3, L = DML, DME (O,O′-coordinating 1,2-dimethoxyethane) and bpy (N,N′-coordinating 2,2′-bipyridine), indicate a rather weak coordination of DML to the Wv centre, the existence of these complexes suggests that the pterin heterocycle coordinates to the metal via N(5) and/or O(4).
W(O)Cl3 或 W(O)2Cl2 与 1,3 二甲基哒嗪(DML)的配位发生在螯合 DML 的 O(4) 和 N(5) 中心。无色的二氧钨(VI)络合物只表现出部分可逆的还原行为,而可氧化的红色单氧钨(V)络合物则很稳定,可通过 EPR、UV-VIS、IR 和 NMR 光谱进行研究。后一种技术通过羰基伸展带的变化和质子共振的顺磁移动来确认配位位点。虽然 (L)W(O)Cl3(L = DML)、DME(O,O′配位的 1,2-二甲氧基乙烷)和 bpy(N,N′配位的 2,2′-联吡啶)的 EPR 结果表明 DML 与 Wv 中心的配位相当弱,但这些配合物的存在表明蝶呤杂环通过 N(5) 和/或 O(4) 与金属配位。