Chemical Reactivity of Electronically Excited Transition Metal Complexes

金属簇合物是一类重要的催化剂，作为催化剂时存在于金属表面的物种模型也引起了人们的极大兴趣。这种簇合物强烈地吸收光，由此形成的高能(激发态)物种在引起有机分子的化学转化方面非常活跃。这一研究项目有望提供有效利用金属团簇作为光诱导化学反应催化剂所必需的信息。建议的研究集中于提供从两类过渡金属化合物开始的多电子光化学的一般指南：多键金属-金属(M-n-M)二聚体和六核簇合物Mo(II)和W(II)。这些化合物的激发态发光强度高，寿命长。控制六核团簇和M-n-M二聚体激发态动力学的因素将用电子吸收光谱、发射光谱和时间分辨光谱来确定。初步数据表明，这些物种的氧化还原化学来源于金属核。研究将通过循环伏安法、计时安培法和电致化学发光(ECL)来识别反应路径。特别重要的是实验，在这些实验中，ECL将被用来探索六核簇氧化还原过程的几个机理特征。光谱和电化学研究是互补的，将被用来定义一个框架，在其中构建激发态金属团簇的多电子转换。基于小分子反应物和有机底物在电子激发、配位不饱和金属簇核上的氧化还原反应的激发态反应路径将被开发出来。

Metal cluster compounds are an important class of catalysts and are also of substantial current interest as models of species which exist at the metal surfaces when they are used as catalysts. Such cluster compounds absorb light strongly and the high-energy (excited state) species which are formed thereby are very reactive in bringing about chemical transformations of organic molecules. This research project is expected to provide information which is essential to effective use of metal clusters as catalysts for light-induced chemical reactions. The proposed research is focused on providing general guidelines for multielectron photochemistry beginning with two classes of transition metal compounds: multiply bonded metal- metal (M-n-M) dimers and hexanuclear clusters of Mo(II) and W(II). The excited states of these compounds are highly luminescent and long-lived. The factors governing the excited state dynamics of the hexanuclear clusters and the M-n-M dimers will be defined using electronic absorption, emission and time-resolved spectroscopies. Preliminary data indicate that the oxidation-reduction chemistry of these species is derived from the metal cores. The studies will be extended by using cyclic voltammetry, chronoamperometry and electrogenerated chemiluminescence (ecl) to identify reaction pathways. Of special importance are experiments in which ecl will be used to probe several mechanistic features of the hexanuclear cluster oxidation-reduction processes. The spectroscopic and electrochemical studies are complementary and will be used to define a framework in which to construct multielectron transformations of excited state metal clusters. Excited state reaction pathways that rely on redox reactions of small molecule reactants and organic substrates at electronically excited, coordinatively unsaturated metal cluster cores will be developed.