Ringexpansion of N-Heterocyclic Carbenes

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Our recent work demonstrates that N-heterocyclic carbenes (NHCs) are by far less stable than generally expected. These molecules undergo ring expansion reactions (RER) with destruction of the NHC core structure especially when they were reacted with main group element (MGE) hydrides. Furthermore, we have shown for the reaction of selected MGE hydrides with NHCs that dehydrogenative element element coupling occurs; the NHC serves in these cases as a hydrogen acceptor. In our future work we want to continue with the systematic investigation of RERs of NHCs and NHC-mediated dehydrocoupling of MGE hydrides, with a focus on the heavier group 13 (Ga/In), group14 (Ge/Sn/Pb), and group 15 (P/As/Sb) elements. Furthermore, we want to explore the use of NHC adducts of group 13 hydrides of the type (NHC)·EH2X and (NHC)∙EHX2 (E = Al, Ga, In), respectively, as synthetic equivalents for subvalent entities “EX” and “EX2“ and we want to answer the question whether our results on the ring exansion of NHCs can be transferred to a possible RER of N-heterocyclic Silylenes in the reaction with MGE halides. Moreover, we want to try to convert the RER products into novel 6-ring carbenes or silylenes.