Nowroozi-Isfahani Taraneh, Musaev Djamaladdin G, McDonald Frank E, Morokuma Keiji
Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322.
Organometallics. 2005 Jun 6;24(12):2921-2929. doi: 10.1021/om050255r.
Mo-catalyzed endo-cycloisomerizations of alkynes tethered to alcohols have been studied using density functional theory, and comparisons were made with the W-catalyzed reaction. The cycloisomerization is initiated with the formation of metal alkyne pi complex and is followed by the rate-determining step, which transforms the pi complex to a vinylidene carbene complex, considered to be critical for endo-mode cyclization. Several different alkynols have been selected to investigate five- and six-membered ring endo-cycloisomerizations in the presence of Mo(CO)(5) catalyst. The energy barriers calculated for five- and six-membered ring cycloisomerizations are within a range of 25-30 kcal/mol for most cases studied, showing no significant energy difference between the two metals. The stabilization effect of THF and Et(3)N solvents and the substitution reaction of THF by alkynol substrates in the reaction process with Mo and W complexes are studied as well. The principal difference between Mo- and W-catalyzed cycloisomerization processes appears to be the initial formation of a pi complex, which is more stabilizing for formation of the W-alkyne vs Mo-alkyne complexes.
利用密度泛函理论研究了钼催化的与醇相连的炔烃的分子内环异构化反应，并与钨催化的反应进行了比较。环异构化反应始于金属炔烃π络合物的形成，随后是速率决定步骤，该步骤将π络合物转化为亚乙烯基卡宾络合物，这被认为是endo-模式环化的关键。选择了几种不同的炔醇来研究在Mo(CO)₅催化剂存在下的五元环和六元环endo-环异构化反应。在大多数研究的情况下，五元环和六元环环异构化反应计算出的能垒在25-30 kcal/mol范围内，表明两种金属之间没有显著的能量差异。还研究了四氢呋喃（THF）和三乙胺（Et₃N）溶剂的稳定作用以及在反应过程中THF被炔醇底物与钼和钨络合物发生的取代反应。钼和钨催化的环异构化过程之间的主要区别似乎在于π络合物的初始形成，对于W-炔烃络合物的形成，π络合物的稳定性比Mo-炔烃络合物更高。
