Siloxyl radical initiated HCN polymerization: computation of N-heterocycles formation and surface passivation
Siloxyl radical initiated HCN polymerization: computation of N-heterocycles formation and surface passivation
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甲硅烷氧基自由基引发的 HCN 聚合：N-杂环形成和表面钝化的计算
DOI：
10.1093/mnras/stac271
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发表时间：
2022
影响因子：
4.8
通讯作者：
DeYonker, Nathan J.
中科院分区：
文献类型：
--
作者：
Fioroni, Marco;DeYonker, Nathan J.
在这项工作中，通过量子化学（密度泛函理论 (DFT)、PW6B95/def2-TZVPP；DLPNO-CCSD(T)/CBS），分析了模型二氧化硅表面上的甲硅烷氧基自由基 (Si-O•) 引发和催化的 HCN 聚合 [(HCN)1 − 4]。线性HCN聚合物(pHCN)是通过SiO•位点上的自由基引发机制获得的，并且由于末端N原子上的自由基定位和C中心上的自由基攻击而具有-(HC-N)-骨架。 NC 杂环是通过线性 SiO-(HCN)3 − 4 的环化形成的，并且在热力学上总是优于其线性对应物，充当热力学汇。天体化学界特别感兴趣的是 N-杂环 1,3,5-三嗪的形成，它可以在相对较低的 T (ΔG†= 23.3 kcal/mol) 下释放到气相中。 SiO-(HCN•) 的完全氢化遵循两个反应通道生成产物：(a)SiO-CH3+•NH2 或 (b) 氨基甲醇 + Si•，但其特点是动力学缓慢。 H2O 与富电子 SiO-(HCN•) 的亲核加成显示出不利的热力学以及高活化能。线性 (HCN)1−4 从 SiO•位点的裂解也显示出较高的热力学能量损失 (ΔG≥82.0 kcal/mol)。因此，硅酸盐表面将被化学活性的“pHCN刷”钝化，从而改变表面的物理化学性质。表面催化 HCN 聚合物表现出高度化学反应性的前景以及形成 1,3,5-三嗪和氨基甲醇的拟议途径为天体化学中复杂有机物质的形成开辟了令人兴奋的新化学途径。
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 by a siloxyl radical (Si-O•) on a model silica surface is analysed. 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 centre. NC heterocycles are formed by cyclization of the linear SiO-(HCN)3 − 4and 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+•NH2or (b)amino-methanol + Si•, though characterized by slow kinetics. Nucleophilic addition of H2O to the electron-rich SiO-(HCN•) shows an unfavourable thermodynamics as well as a high-activation energy. The cleavage of the linear (HCN)1−4from 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-catalysed HCN polymers exhibiting a high degree of chemical reactivity and proposed avenues for the formation of 1,3,5-triazine and amino-methanol opens exciting new chemical pathways to Complex Organic Matter formation in astrochemistry.