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INORGANIC AND ORGANOMETALLIC CHEMISTRY
1. Reactivity of Transition Metal-Carbon Multiple Bonds
A major project of my group is concerned with the reactivity of metal-carbon multiple bonds. The long-range goal is the development of selective bond-forming processes. Our work is focusing on transition metal alkylidyne complexes, i. e. compounds containing metal-carbon triple bonds. In recent years, we studied coupling reactions of alkylidyne ligands with other terminal ligands such as carbonyl, isocyanide, and thiocarbonyl ligands. The coupling of two alkylidyne ligands was also demonstrated. Coupling reactions of alkylidyne ligands with other ligands such as alkylidene, imido, oxo, alkyl, aryl, alkynyl ligands will be explored. In this work, we are primarily interested in the fundamental aspects of the bond-forming steps. The potential of low-valent transition metal alkylidyne complexes as reagents in organic synthesis is only beginning to be realized. In an effort to establish a rational basis for the development of this chemistry, we investigate reactions of alkylidyne metal complexes with alkenes, alkynes and other unsaturated organic substrates. These reactions are useful for the construction of larger organic systems within the coordination sphere of transition metal centers.
2. Metal-Carbon Multiple Bonds as Functional Components in Molecular Materials
Metal-carbon triple bonds provide a means of strong electronic coupling between metal centers and organic p systems. This feature and the presence of low-energy metal-to-alkylidyne charge transfer transitions make metal-carbon triple bonds promising as components in molecular materials. Furthermore, metal-carbon triple bonds are thermally rather stable entities, and reliable synthetic methods are available to fine-tune the electronic properties of metal alkylidyne complexes. Several functionalized tungsten alkylidyne complexes of the Fischer-type have been designed for the study of the following aspects: nonlinear optical properties, photo-induced directional electron transfer, and photo-induced energy transfer. Modifications of the systems to form liquid crystals are being explored.
3. Synthesis of Molecular Solid-State Materials by the Self-Assembly of Stable Transition Metal Complex Building Blocks
A new project in our group is concerned with the synthesis of molecular materials based on the assembly of stable transition metal complex building blocks. The basic synthetic strategy is based on the use of special bi- (or multi-) functional ligands. One functionality is a strongly ligating site. It is used to form the stable transition metal complex building blocks of defined geometry and size. The other function is a site capable of weak interactions, such as a weakly coordinating site or a hydrogen bonding site. The building blocks are interconnected in a geometrically defined manner via the weak interaction sites. The goal is to achieve control over the supramolecular structures and physical properties on the new materials via the nature of these transition metal complex building blocks. Thus by proper choice of transition metal centers (electron configuration and coordination geometry) and spacer ligands (length, steric and electronic properties) it may be possible to determine the dimensions of the new materials and influence their electronic properties. Presently, we are focusing on the use of transition metal complexes of bifunctional isocyanides as the building blocks.
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