Synthesis of Novel Chelating N-Heterocyclic Carbenes and Their Heavier Analogues as Tools in Coordination Chemistry

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N-Heterocyclic carbenes (NHCs) have been attracting worldwide interest because of their considerable potential in coordination/organometallic chemistry, catalysis and materials science. In recent years, stable N-heterocyclic silylenes (NHSis), the silicon analogues of NHCs, are no longer laboratory curiosities but valuable building blocks for new functional silicon compounds. Particularly, NHSis can act as very effective sigma-donor ligands toward low-valent main group elements and transition-metals to form novel types of complexes with currently unknown and promising chemical behavior. The goal of this project is to develop new NHC and NHSi chelate systems that serve as effective supporting ligands for the stabilization of currently unknown main-group (Si, Ge, Sn, Pb, B, Al, Ga, etc.) and transition metal (Mn, Fe, Co, Ni, etc.) complexes. The complexes are expected to show particular reactivities because of the unusual low oxidation states of the central atoms. The resulting chelate ligand supported low-valent compounds are highly reactive with respect to the activation of small molecules and thus useful for chemical transformations of substrates which are otherwise hard to achieve. Moreover, the silylene-containing target systems, featuring at least one divalent silicon center, are even capable to facilitate the activation of small molecules without the presence of a metal (‘metal-free’) and can lead to value-added coupling products of organic substrates such as the heterocoupling of CO and isocyanides to give ketimines. Not only for better understanding but eventually to derive at the level of predicting their steering role in coordination chemistry, the synthesis and reactivity patterns of NHC and NHSi chelate ligands,related sigma-donor systems such as phosphine, pyridine and even those of the currently unknown bis-phosphinidene and bis-borylene moieties are included in this investigation.