Siloxyl radical initiated HCN polymerization: computation of N-heterocycles formation and surface passivation

ABSTRACT In this work, by means of quantum chemistry (Density Functional Theory (DFT), PW6B95/def2-TZVPP; DLPNO-CCSD(T)/CBS), HCN polymerization [(HCN)1 ? 4] initiated and catalysed a siloxyl radical (Si-O•) on model silica surface is analysed. Linear polymers (pHCN) are obtained mechanism at SiO• site characterized -(HC-N)- skeleton due to localization the terminal N atom attack C centre. NC heterocycles formed cyclization linear SiO-(HCN)3 4 always thermodynamically preferred over their counterparts, acting as thermodynamic sinks. Of particular interest astrochemistry community formation N-heterocycle 1,3,5-triazine that can be released into gas phase relatively low T (?G† = 23.3 kcal/mol). Full hydrogenation SiO-(HCN•) follows two reaction channels with products: (a) SiO-CH3 + •NH2 or (b) amino-methanol Si•, though slow kinetics. Nucleophilic addition H2O electron-rich shows an unfavourable thermodynamics well high-activation energy. The cleavage (HCN)1?4 from also high energy penalty (?G?82.0 As consequence, silicate will passivated chemically active ‘pHCN brush’ modifying physico-chemical properties. prospect surface-catalysed exhibiting degree chemical reactivity proposed avenues for opens exciting new pathways Complex Organic Matter in astrochemistry.