Cl3Si(NH)BCl2, i.e., [(trichlorosilyl)amino]dichloroborane or TADB may act as a molecular precursor in syntheses to high-demand Si/B/N ceramics. To build a ceramic such as Si3B3N7. one may use liquid ammonia as the network forming agent. The actual processes which lead to such amorphous material are not yet fully understood. With this work. we aim at a quantification of product formation probabilities during initial reactions of TADB with NH3. For this reason, we have investigated the less complicated case of various gas-phase reactions with perturbation theory, and the situation in the liquid phase Will be published separately, In more detail, the reactions comprise (a) the first and second ammonolysis of TADB, (b) the decomposition of adducts (H3N --> SiCl3NHBCl2 and H3N --> BCl2NHSiCl3.). (c) the dimerization of TADB, and finally (d) a continuing reaction of TADB with the most probable product of the first ammonolysis of TADB (which we term TACBA, trichlorosilylaminochloroboryl amine). Besides these initial steps. and because of the significance of their products, reactions of TACBA with other TACBA molecules and formations of borazine derivates have also been looked into. Our results confirm qualitative chemical intuition: The major primary process in the gas phase is a substitution at the boron center of TADB to yield TACBA. Also. it can be seen that the dissociation of the H3N --> BCl2NHSiCl3 adduct into BCl2NH2 and SiCl3NH2 is a side reaction. Albeit, in the continuing stage, the trimerization of TACBA under formation of a borazane six-membered ring releases much more energy than competing processes and is therewith important. As further reactions to be taken into consideration, we find a branching of the molecular backbone accompanied by a break-up of the Si-N-B unit in TADB and a second ammonolysis at the boron side of TACBA. Linking monomer units becomes energetically less and less probable as the ammonolyses of Si-Cl and B-Cl bonds proceed.