Lammertsma Koop, Ehlers Andreas W, McKee Michael L
Department of Chemistry, Vrije Universiteit, Amsterdam, The Netherlands.
J Am Chem Soc. 2003 Dec 3;125(48):14750-9. doi: 10.1021/ja0349958.
Density functional theory is used to explore the mechanism of the copper(I)-chloride-catalyzed decomposition of W(CO)(5)-complexed 7-phosphanorbornadiene and the subsequent olefin trapping of the terminal phosphinidene complex. CuCl lowers the activation barrier by interacting directly with the breaking P-C bond. Contrary to the prevailing notion that a free terminal phosphinidene complex (W(CO)(5)=PR) is generated in the CuCl-catalyzed cheletropic elimination of the 7-phosphanorbornadiene-W(CO)(5) complex, the present mechanism suggests that CuCl is attached to the terminal phosphinidene. Furthermore, a "chloride shuttle" takes place where the chloride first migrates to the phosphorus center and then is returned back to the copper center by the incoming olefin in an S(N)2 reaction step. When the substituent on phosphorus is a phenyl group (R = Ph), the uncatalyzed reaction has an activation barrier of 17.9 kcal/mol, which is reduced by 10.9 kcal/mol on including the CuCl catalyst. The CuCl-catalyzed decomposition of 7-phosphanorbornadiene followed by olefin trapping of the terminal phosphinidene complex has a close parallel with the Cu(I)-catalyzed cyclopropanation reaction of diazoalkane. In both catalyzed reactions, copper(I) is coordinated to the phosphinidene/carbene as a Lewis acid, while a Lewis base is displaced from the phosphorus/carbon center as the olefin is added.
密度泛函理论用于探究氯化亚铜催化的W(CO)(5)络合的7-磷降冰片二烯分解机理以及随后末端磷烯络合物的烯烃捕获过程。氯化亚铜通过与断裂的P-C键直接相互作用降低了活化能垒。与普遍认为在氯化亚铜催化的7-磷降冰片二烯-W(CO)(5)络合物的螯变消除反应中生成游离末端磷烯络合物（W(CO)(5)=PR）的观点相反，目前的机理表明氯化亚铜附着在末端磷烯上。此外，发生了一个“氯穿梭”过程，其中氯首先迁移到磷中心，然后在一个S(N)2反应步骤中被进入的烯烃返回到铜中心。当磷上的取代基为苯基（R = Ph）时，未催化反应的活化能垒为17.9 kcal/mol，加入氯化亚铜催化剂后降低了10.9 kcal/mol。氯化亚铜催化的7-磷降冰片二烯分解，随后末端磷烯络合物的烯烃捕获过程与氯化亚铜催化的重氮烷环丙烷化反应密切平行。在这两个催化反应中，亚铜离子作为路易斯酸与磷烯/卡宾配位，而当加入烯烃时，一个路易斯碱从磷/碳中心被取代。
