Studies on the main group-based aromatic compounds : 1,4,2-Diazaborole and Germanium(0) species
Date of Issue2018
School of Physical and Mathematical Sciences
Aromaticity is one of most important concepts in the chemistry. Recently, a variety of aromatic molecules containing main group elements have been extensively studied, which show some unique electronic property. However, in contrast to the classical methods widely applied in organic chemistry, the preparation of such aromatic compounds seems a big challenge due to the requirement of the novel synthetic approaches. Given the importance of aromatic compounds involving main group elements, the development of unique framework is desirable from both fundamental and application points of views. Among them, by installation of a boron atom into ring system with the electronegative nitrogen atom, a series of aromatic B,N-containing heterocycles have been developed with the dramatic advance in synthetic route. In this thesis, a new family of aromatic five-membered B,N-heterocyclic rings, namely 1,4,2-diazaboroles, were introduced and fully characterized. Due to their unique electronic structures, the interesting reactivity was also studied including nucleophilic reactivity of the boron center, borylene insertion, photo-induced isomerization and elimination. Moreover, by utilization of an imino-N-heterocyclic carbene, we successfully isolated a novel germanium(0) species which can be viewed as a mesoionic germylene. The solid-state structure and computational studies disclosed that the electron delocalization over the C2N2Ge ring with the participation of one lone pair on Ge atom, thus supporting its aromaticity. Its nucleophilic properties as one or two lone pairs donor were confirmed by the reactions with MeOTf and transition metal complexes (Cr, Mo, W, Ir). Thus, in this thesis we have demonstrated that by use of N-heterocyclic carbene as the supporting ligand several novel aromatic species containing boron or germanium elements could be isolated successfully. Some unusual reactivity has been also investigated due to their unique electronic structures.