Control of Electron Transfer Reactions on the Basis of Dynamic Intramolecular Coordination

目前的工作源于我们早期的观察，即羰基、烷氧基和吡啶基的引入降低了四烷基锡烷的氧化电位。光谱学未发现中性分子中的配位现象。因此，氧化电位的降低似乎归因于阳离子自由基中间体与锡的动态分子内配位。这种配位稳定了阳离子自由基，从而有利于电子转移，也控制了键裂解的选择性。吡啶基已被发现在检查中特别有效。从而形成了一类新的电助剂[2-（2-吡啶基）乙基]二甲基硅基。α-硅醚和硫化物在硅原子上引入2-（2-吡啶基）乙基，使其氧化电位降低。基于核磁共振谱、从头算分子轨道计算和氧化的溶剂效应的研究表明，氧化势的降低是由于吡啶基与硅的“分子内动态配位”。通过竞争实验，比较了该新型电助剂与三甲基硅基、三基锡基的反应性。本研究表明，利用动态分子内配位对电助剂的反应性进行微调是可行的。

The present work stems from our earlier observations that the introduction of carbonyl, alkoxy, and pyridyl groups decreases the oxidation potential of tetraalkylstannanes. There is no indication of the coordination in the neutral molecule by the spectroscopy. Therefore, the decrease of the oxidation potential seems to be attributed to the dynamic intramolecular coordination to tin in the cation radical intermediates. Such coordination stabilizes the cation radical which in turn favors the electron transfer and also controls the selectivity of the bond cleavage. Pyridyl group has been found to be especially effective among the examined.Thus new class of electroauxiliary, [2-(2-pyridyl)etyl]dimethylsilyl group has been developed. Introduction of 2-(2-pyridyl)ethyl group on silicon atom of α-silylethers and sulfides gives rise to decrease of their oxidation potentials. Studies based on NMR spectra, ab initio molecular orbital calculations, and solvent effect of oxidation have suggested that the decrease of the oxidation potentials is attributed to the 'dynamic intramolecular coordination' of pyridyl group to silicon. The reactivity of this new electroauxiliary has been compared with those of trimethylsilyl group and tributylstannyl group by competition experiments. The present study indicates the feasibility of fine tuning of the reactivity of electroauxiliaries using dynamic intramolecular coordination.