In this work, by means of quantum chemistry (DFT, PW6B95/def2-TZVPP; DLPNO-CCSD(T)/CBS), HCN polymerization [(HCN)1 − 4] initiated and catalyzed by a siloxyl radical (Si-O•) on a model silica surface is analyzed. Linear HCN polymers (pHCN) are obtained by a radical initiated mechanism at a SiO• site and are characterized by a -(HC-N)- skeleton due to radical localization on the terminal N atom and radical attack on the C center. NC heterocycles are formed by cyclization of the linear SiO-(HCN)3 − 4 and are always thermodynamically preferred over their linear counterparts, acting as thermodynamic sinks. Of particular interest to the astrochemistry community is the formation of the N-heterocycle 1,3,5-triazine that can be released into the gas-phase at relatively low T (ΔG†=23.3 kcal/mol). Full hydrogenation of SiO-(HCN•) follows two reaction channels with products: a) SiO-CH3+•NH2 or b) aminomethanol+Si•, though characterized by slow kinetics. Nucleophilic addition of H2O to the electron rich SiO-(HCN•) shows an unfavorable thermodynamics as well as a high activation energy. The cleavage of the linear (HCN)1 − 4 from the SiO• site also shows a high thermodynamic energy penalty (ΔG≥82.0 kcal/mol). As a consequence, the silicate surface will be passivated by a chemically active “pHCN brush” modifying the surface physico-chemical properties. The prospect of surface-catalyzed HCN polymers exhibiting a high degree of chemical reactivity and proposed avenues for formation of 1,3,5-triazine and aminomethanol open exciting new chemical pathways to COM formation in astrochemistry.
