Nguyen Huyen Thi, Nguyen Minh Tho
Department of Chemistry, University of Leuven, B-3001 Leuven, Belgium.
Phys Chem Chem Phys. 2015 Jul 14;17(26):16927-36. doi: 10.1039/c5cp01456e.
Thermally feasible decomposition pathways of formamide (FM) in the presence of vanadium VO(X(4)Σ(-)) and titanium TiO(X(3)Δ) monoxides are determined using density functional theory (BP86 functional) and coupled-cluster theory (CCSD(T)) computations with large basis sets. These diatomic metal oxides have been shown to be present in the prebiotic conditions. The dehydration, decarbonylation and dehydrogenation reactions of the molecular and dissociative complexes of FM and MO (M = V, Ti) turn out to be more favourable than those of the ground state isolated FM. The effect of addition of one or two water molecules on energy barriers is also probed for these reaction pathways. In some cases, a combined catalytic effect when adding water is observed. This enhanced catalytic effect was not observed in previously reported cases of FM transformation, for example, when adding water molecules into the mineral-catalyzed isomerizations of FM. The dehydration process of MO-FM complexes without the presence of water is found to be more feasible than the decarbonylation and dehydrogenation. The overall energy barrier for the non-water VO-FM dehydration is ∼3 kcal mol(-1) lower than the reference energy of the separated systems, whereas those of the two latter reactions are higher than the reference. Although the TiO-FM dehydration has a larger overall barrier of 14 kcal mol(-1) as compared to the VO-FM counterpart, the two other decomposition pathways still have much higher energy barriers. Direct formation of urea and H2CO from a FM dimer and indirect formation of urea from FM via the intermediate HNCO are also established. Urea formation in an indirect pathway is preferred. These low-energy-barrier pathways leading to the formation of important prebiotic molecules suggest that metal monoxides MO could play an important catalytic role in the prebiotic reactions of FM.
采用密度泛函理论（BP86泛函）和耦合簇理论（CCSD(T)）并结合大基组，确定了在钒VO(X(4)Σ(-))和钛TiO(X(3)Δ)单氧化物存在下甲酰胺（FM）的热可行分解途径。这些双原子金属氧化物已被证明存在于益生元条件下。FM与MO（M = V、Ti）的分子和离解配合物的脱水、脱羰和脱氢反应比基态孤立的FM更有利。还研究了添加一个或两个水分子对这些反应途径能垒的影响。在某些情况下，观察到加水时的联合催化作用。在先前报道的FM转化案例中未观察到这种增强的催化作用，例如，当向FM的矿物催化异构化中添加水分子时。发现不存在水时MO - FM配合物的脱水过程比脱羰和脱氢更可行。非水VO - FM脱水的总能量垒比分离体系的参考能量低约3 kcal mol(-1)，而后两个反应的能量垒高于参考能量。尽管与VO - FM相比，TiO - FM脱水的总能量垒更大，为14 kcal mol(-1)，但另外两条分解途径的能量垒仍然高得多。还确定了由FM二聚体直接形成尿素和H2CO以及通过中间体HNCO由FM间接形成尿素的过程。间接途径形成尿素更有利。这些导致重要益生元分子形成的低能量垒途径表明，金属单氧化物MO可能在FM的益生元反应中发挥重要的催化作用。
