Low-valent Main Group Compounds
The physical properties and chemical reactivities of main group elements generally depend on the number of valence electrons. For this reason, elements with the same number of valence electrons generally have similar chemical and physical properties. One of the fundamental interests in chemistry is to consistently understand the similarities and differences of the elements and their compounds, particularly those in the same periodic group. Low-coordinated compounds of carbon play an integral role in organic chemistry and have been the subject of intense study for nearly 200 years. On the other hand, the first low coordinate compound of silicon was synthesized in 1981. Since this time heavier element analogues of low-coordinate organic compounds have fascinated chemists both in the field of organic and inorganic chemistry because despite their isovalent nature they often have unique chemical features.
Main group compounds have shown their ability to mimic transition metals through their ability to activate relatively inert bonds under mild conditions. However in order to offer a true ‘eco-friendly’ alternative to transition metals their catalytic potential is yet to be fully realized. Research within the Inoue group focuses on the synthesis, characterization and reactivity of novel low-oxidation state group 13, 14, and 15 complexes. With the overall aim to understand the key processes in enabling catalytic turnover via a combined experimental and theoretical approach. So far we have developed our understanding of the role of ligand design in the stabilization of these low-oxidation species but also their role in enabling oxidative addition of small molecules and substrates. Challenges still remain in reductive elimination chemistry, but recent discoveries from our group have shown it is possible to use these reactive earth abundant metals in catalysis.
Transition Metal Complexes with Silicon Based Ligands
Organometallic compounds containing metal-carbon multiple bonds are indispensible ingredients of many chemical transformations especially catalytic reactions, which are becoming increasingly important for waste-free (sustainable) processes particularly in oil industry. An enormous impact in this field has its origins in the seminal works of E. O. Fischer (Nobel laureate 1973), who synthesized the first organometallic species with carbon metal multiple bonds, and R. Schrock, R. Grubbs, and Y. Chauvin (Noble laureates 2005), who discovered that certain unsaturated organometallic species are incredibly efficient catalysts in all types of olefin metathesis reactions, an invaluable synthetic tool for organic chemists. While metal-carbon multiple bonded systems are well established and can serve as highly efficient catalytic systems, heavier homologues, such as metal-silicon multiple bonded complexes, are scarce. These novel metal silicon complexes are expected to serve as powerful and selective catalysts capable of activating small and relatively unreactive molecules, which can be used in the efficient syntheses of complex organic molecules, pharmaceuticals, polymers, and a broad spectrum of value-added products. The focus of this project is to synthesize novel reagents and catalysts based on silicon-metal complexes and then to use these species in the development of efficient catalytic processes. In particular processes that activate small molecules such as methane (the main component of natural gas) and ammonia will be investigated. Small molecule activation is a vital area of chemistry that will make it possible to efficiently convert simple feed stock chemicals into complex value added products with minimal waste.
Main Group Metal Hydrides
Main group metal hydrides have recently attracted widespread attention because of their applications in organic synthesis and material sciences. For example, hydrometalation using main group metal hydrides has developed into one of the most important synthetic methods. Moreover, compounds with M-H bonds are often efficient hydrogen transfer-reagents and may react with unsaturated functionalities, as well as organic radicals. Accordingly, many main group metal hydrides are powerful reducing agents and allow for the transformation of compounds with inert element-element bonds into more reactive species. Metal hydrides are considered as fuel storage-materials with reasonable prospects in a hydrogen-based alternate energy-supply concept. Deposition-coating processes (e.g. CVD, PVD) are another field of application for this type of compounds. To date, a large number of main group metal hydrides has been prepared and very often reactivity adjustment is realized by steric congestion and by attaching strongly electron-donating substituents to the metal center. This research project focuses on the synthesis and reactivity of novel hydrido complexes of main group metals (e.g. B, Al, Ga, Si, Ge, Sn, etc.) through the use of tailor-made ligand systems. In particular, the activation of comparably unreactive bonds such as C-H, C-O, C-N and C-C, often found in organic substrates, or of element-element bonds in feedstock materials (e.g. elemental phosphorus, sulfur) is a major topic of interest. Furthermore, the catalytic hydrogenation of unsaturated functional groups (e.g. C=O, C=N, C=C) applying these main group metal hydrides will be investigated.