Chemistry of Bulky Alkoxide/Siloxide Complexes: Homogeneous Metal Oxides

拟议研究的重点是金属化合物的合成和化学反应，其中金属连接到几个大基团，这些基团通过空间拥挤阻止金属与尽可能多的其他原子成键。这些所谓配位不饱和物种中的金属原子是缺电子的，这导致它们表现出与金属氧化物相当的反应性。这些化合物已被发现能够活化一氧化碳和大气中的氧气，它们的反应在有机化合物的合成和更清楚地理解金属氧化物的多相催化方面具有重要的潜在意义。该项目的一个主要目标是阐明三叔丁基甲醚(TRITOX)和三叔丁基硅氧烷(Silox)配体的Zr和Ta络合物对小分子的活化机理。动力学同位素效应和自由基探针将被用来证实双三氧锆络合物对氧的活化是基于自由基的。作为Fischer-Tropsch合成的第一步，三(三氧基)Ta对CO的解离吸附模型将被研究。金属氢化物辅助二氢双(硅氧烷)Ta裂解CO的细节将作为单一序列的一个独特例子进行研究，该序列涉及均相Fischer-Tropsch反应、CO还原、脱氧和C-C键的形成。

The focus of the proposed research is the synthesis and chemical reactions of metal compounds in which the metal is attached to several bulky groups which by steric crowding prevent the metal from making bonds to as many other atoms as it would if it could. The metal atoms in these so-called coordinatively unsaturated species are electron deficient, which causes them to manifest reactivities which are comparable to metal oxides. These compounds have been found to be capable of activating carbon monoxide and atmospheric oxygen, and their reactions are potentially of great importance in the synthesis of organic compounds and in providing a clearer understanding of heterogenous catalysis by metal oxides. A primary objective of the project is to elucidate the mechanisms of activation of small molecules by Zr and Ta complexes of tri-tertiary-butylmethoxide (tritox) and tri-tertiary-butylsiloxide (silox) ligands. Kinetic isotope effects and radical probes will be used to substantiate that the activation of dioxygen by a bis-tritoxZr complex is radical based. The cleavage of CO by tris(tritox)Ta will be studied as a model of the dissociative adsorption of CO, the initial step in Fischer-Tropsch synthesis. The details of the metal-hydride assisted cleavage of CO by dihydridobis(silox)Ta will be investigated as a unique example of a single sequence which involves a homogeneous Fischer-Tropsch reaction, CO reduction, deoxygenation and C-C bond formation.