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Abstract

A new synthetic route to N-heterocyclic carbenes (NHCs) with cyclophanic architecture is described. Using this approach, the electronic and structural parameters of an imidazopyridine-based carbene could be uncoupled. The electronic cross-talk between the cyclophane-layers made it possible to change the electronic properties without any constitutional redesign. Although the σ-donor-properties of the cyclophane-based carbene is comparable to its planar cousin, the results of theoretical (DFT-calculations) as well as experimental (IR, CV, X-ray) studies suggested that it is much easier to tune its π-acceptor-properties. Furthermore, reactivity data demonstrated that the outcome of three mechanistically distinct gold-catalyzed reactions was determined by changing the π-acceptor-properties of the particular NHC that is used.
The second part of this dissertation deals with the synthesis and characterization of phosphorus-based aminoylid carbenes (AYCs) and with the synthesis of homo- as well as heteronuclear bimetallic AYCs. Theoretical (DFT), experimental (CV, IR) as well as reactivity data gave some insights into the ambivalent electronic properties of AYCs. On the one hand IR-data indicated that this type of carbene is one of the strongest σ-donors known nowadays. On the other hand reactivity data, e. g. of a gold (I) catalyzed enallene cycloaddition, also gave evidence for their distinctive π-acceptor-properties. Using a silver-carbene approach several different mono- and heteronuclear bimetallic AYCs could be synthesized.