The termination of semiconductor surfaces plays a major role in surface reactivity and in our ability to create a well defined and sharp interface between a semiconductor and a thin film, often required for practical applications. Although hydrogen termination of group IV semiconductors is often a good starting point for deposition chemistry, the reactivity of hydrogen terminated surfaces is often limited. Here we selectively produce a specific NHx termination of Si(100) surface by exposing it to ammonia and briefly annealing at a predetermined temperature. The reactivity of silicon surfaces prepared in such a way is examined by reacting them with a common organometallic precursor for thin diffusion barrier film growth, tetrakis(dimethylamido)titanium, TDMAT. Experimental observations suggest the occurrence of a surface transamination reaction, where an approaching TDMAT molecule reacts with a surface NHX site, eliminating dimethylamine and attaching Ti to the surface N atom. Vibrational spectroscopy holds the key to determining this reactivity and surface reaction pathways. Together with temperature programmed desorption and computational DFT investigations, these studies expand the generality of transamination processes to other amines on Si(100). The role of steric and electronic factors is evaluated for improving proposed deposition schemes.