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|標題:||Density functional studies on dicobalt octacarbonyl mediated urea formation from primary amine||作者:||Hong, F.E.
|關鍵字:||catalytic oxidative carbonylation;selenium-assisted carbonylation;carbon-monoxide;cyclic ureas;aliphatic-amines;aromatic-amines;metal;complexes;aniline;alkoxycarbonylation||Project:||Organometallics||期刊/報告no：:||Organometallics, Volume 23, Issue 4, Page(s) 718-729.||摘要:||
Two adiabatic potential energy surfaces (PES) are employed for probing the process of the formation of the urea-like compound CH3HNC(=O)NHCH3, which is mediated by dicobalt octacarbonyl from the primary amine NH2CH3, by utilizing the density functional theory method at the B3LYP/631LAN level. These two reaction pathways described here are route 1, which is designated as an insertion-addition pathway, and route 2, an addition-insertion pathway. Elementary steps for both reaction pathways, including the amino group migration to the Co-CO bond, additional NH2CH3 molecule association, oxidative addition of the coordinated amine proton to the cobalt center, and reductive elimination of -C(=O)NHCH3 with -NH2CH3, are modeled and examined. Rather small energies for activation (DeltaG(double dagger)), 2.3 and 2.1 kcal/mol for routes 1 and 2, respectively, are observed for the process of amino group migration and the formation of the Co-carbamyl bond in both routes. The results are in contrast to the alkyl group migration in RCo(CO)(4) cases, in which much higher energies are required. The oxidative addition process of the N-H bond is established as the rate-determining step (rds) for both routes, and the activation energies DeltaG(double dagger) are 49.2 and 56.8 kcal/mol for routes 1 and 2, respectively. All the elementary steps are thermodynamically favorable, except for the oxidative addition process of the N-H bond to the cobalt center. These large energy barriers are responsible for the rigorous reaction conditions required in common transition-metal-mediated urea formation reactions and the low to medium yield in our previously reported cobalt carbonyl mediated urea-like compound formation from propargylamine. On the whole, route 2 is an energetically less favorable and more complicated reaction pathway than route 1. Furthermore, another compound, a formamide derivative, is predicted as a potential product from a competitive reaction of route 1 by our theoretical study. The process has a DeltaG(double dagger) value smaller than that of the formation of the urea product. Nevertheless, there has been no experimental evidence for the formation of formamide until now.
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