Theoretical Studies of Main Group Organometallic Chemistry

本研究得到了美国国家科学基金会理论与计算化学项目的支持。改进的计算技术将在通用原子和分子电子结构系统（GAMESS）程序中实施。这包括开发和实现使用大规模并行计算机对大分子进行电子结构计算的方法，以及处理溶剂效应的计算方法。电子结构理论与动力学相结合，以获得对热力学和动力学性质的定性和定量理解。该理论应用于：(a)主基团和过渡金属之间的单键和多键的解释，(b)应变环和高价键的理论分析，(c)主基团有机金属反应的势能面计算和反应机理预测。具体反应包括：(a)氢化和偶联反应，(b)单分子分解和异构反应，(c)多键化合物的反应。电子结构理论将分子或分子组合视为电子和原子核强烈相互作用的机械系统。原则上，所有的化学行为都可以通过求解这个多粒子系统的量子力学运动方程来理解，但经验表明，要达到对中等大分子的化学性质进行可靠预测所需的精度，需要进行非常繁重的计算。随着现代超级计算机的出现，特别是大规模并行计算机的出现，这已经成为理论化学研究的一个活跃领域。这个项目就是这类研究的一个例子。它强调将该理论应用于碳、硅和钛的化合物，以及这些元素与含有过渡金属原子（如铁）的有机分子的结合。特别令人感兴趣的是具有不寻常化学键结构的中等大小的分子，如应变环或双键，如C=Si或Si=Si。对这些不寻常分子的几何形状和能量学的详细研究有助于我们设计出更大的分子，这些分子具有相同的键合特征，或者可能是由具有这些特征的瞬态物种参与的化学反应形成的。

This research is supported by the NSF theoretical and computational chemisty program. Improved computational techniques will be implemented in the General Atomic and Molecular Electronic Structure System (GAMESS) program. This includes the development and implementation of methods for performing electronic structure computations for large molecules using massively parallel computers, and computational methods for treating solvent effects. Electronic structure theory is combined with dynamics to obtain a qualitative and quantitative understanding of both thermodynamic and kinetic properties. The theory is applied to: (a) the elucidation of single and multiple bonds between main group and transition metals, (b) theoretical analysis of strained rings and hypervalent bonding, and (c) the computation of potential energy surfaces for and the prediction of reaction mechanisms of main group organometallic reactions. Specific reactions include: (a) hydrosilation and coupling reactions, (b) unimolecular decompositions and isomerations, and (c) reactions of multiply bonded compounds. Electronic structure theory treats a molecule, or a molecular assembly, as a mechanical system of strongly interacting electrons and nuclei. In principle, all chemical behavior can be understood by solving the quantum mechanical equations of motion of this many-particle system, but experience shows that very heavy computations are required to achieve the accuracy required to make reliable predictions of the chemical properties of moderately large molecules. With the advent of modern supercomputers, particularly, of massively parallel computers, this has become an active field of theoretical chemical research. This project is an example of such research. It emphasizes the application of the theory to compounds of Carbon, Silicon, and Titanium and the bonding of these elements to organic molecules containing transition-metal atoms such as iron. Of particular i nterest are moderately small molecules with unusual chemical bond structures such as strained rings or double bonds such as C=Si or Si=Si. Detailed study of the geometries and energetics of such unusual molecules contributes to our ability to design much larger molecules which possess these same bonding features or perhaps are formed by chemical reactions involving transient species which possess them.