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，其中金属附着在几个大的基团上，这些基团通过空间拥挤阻止金属与尽可能多的其他原子形成键。这些所谓的配位不饱和物质中的金属原子是缺乏电子的，这使得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激活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对金属氧化物的多相催化提供更清晰的认识方面具有潜在的重要意义。该项目的主要目的是阐明三叔丁基甲氧基（tritox）和三叔丁基硅氧化物（silox）配体的Zr和Ta配合物对小分子的活化机制。动力学同位素效应和自由基探针将被用来证实双-三氧化锆配合物对二氧的活化是基于自由基的。三（三氧化三）Ta对CO的裂解作用将作为CO离解吸附的模型进行研究，这是费托合成的第一步。金属氢化物辅助二氢化氢（硅氧烷）Ta解理CO的细节将作为一个单一序列的独特例子进行研究，该序列涉及均匀的费托反应，CO还原，脱氧和C-C键形成。

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.