SUBSTITUENT-DEPENDENT STEREOSELECTIVE SYNTHESIS OF HEXA-FUNCTIONALISED BORAZINES

In the growing field of polycyclic aromatic hydrocarbons, the doping by heteroatoms has emerged as one of the most versatile approaches to tune the optoelectronic properties of the materials. In particular, borazine derivatives attracted a lot of attention in the last years. While their synthesis, functionalisation and possible use in a broad spectrum of applications have previously been investigated, the effect of different substituents on the formation of the borazine ring and its functionalisation at the boron site has yet to be addressed. This doctoral thesis aims at filling this gap through an in-depth study of the synthesis of novel borazines derivatives. Before addressing the detailed investigations of this thesis work, Chapter I of this manuscript introduces a brief insight into the history and generalities of borazines in the literature since its discovery in 1926 by Stock and Poland. This Chapter also includes the description of the synthetic approaches used for their production, as well as the chemical properties, stability and material applications. The second Chapter of this manuscript describes the investigations developed toward the elucidation of the substituent’s effect during the functionalisation at the boron site of the borazine core. Following a [1+1’+1+1’+1+1’] hexamerisation route toward the formation of the borazine core (using an amino precursor and boron trichloride), the latter can be further functionalised by the addition of a nucleophile, which leads to the formation of stable borazine derivatives. Accordingly, the synthesis of multiple borazine moieties has been performed, using only one type of amino-precursor (aniline) and different organometallic derivatives during the functionalisation step. These organometallic moieties consist of aryl groups that contain one or two ortho-substituents, which allows for a partial- or full-protection of the borazine core, respectively. In the first case, the control of the stereoselectivity of the process in a reaction in which two different isomers (cc and ct) can be formed, is the main focus of this study. Finally, the chemical compatibility and the stability of this novel class of partially-protected borazine moieties developed along this doctoral thesis is also discussed. Encouraged by the results obtained in Chapter II, the study developed in Chapter III aims at bringing light to the effect of the substituents on the formation of the borazine core together with the subsequent functionalisation toward the preparation of stable borazine moieties. For this purpose, the formation of the borazine core has been followed by reaction of different amino-precursors with boron trichloride. The later functionalisation at the boron site can lead to the formation of stable borazine derivatives, depending on the nature of the amino precursor.