Physical Organic Chemistry of Transition Metal Carbene Complexes. 27. Substituent Effects on the Nucleophilic Substitution of [Aryl(thiomethyl)carbene]pentacarbonylchromium(0) Complexes by Amines in Aqueous Acetonitrile
作者:Claude F. Bernasconi、Santanu Bhattacharya
DOI:10.1021/om020955l
日期:2003.3.1
A kinetic study of the reactions of (CO)5CrC(SMe)C6H4Z (Z = 4-CF3, 4-Cl, 4-F, 4-Me, 4-MeO, and 4-Me2N) with n-butylamine, 2-chloroethylamine, piperidine, and 1-(2-hydroxyethyl)piperazine in 50% MeCN−50% water (v/v) at 25 °C is reported. In all cases the nucleophilic attachment of the amine to the carbene complex is rate limiting, which contrasts with the previously reported aminolysis of the methoxy
(CO)5 Cr C(SMe)C 6 H 4 Z(Z = 4-CF 3,4 -Cl,4-F,4-Me,4-MeO和4-Me 2的反应动力学研究N)在25°C下于50%MeCN-50%水(v / v)中的正丁胺,2-氯乙胺,哌啶和1-(2-羟乙基)哌嗪进行了报道。在所有情况下,胺与卡宾配合物的亲核连接均受速率限制,这与先前报道的甲氧基类似物((CO)5 Cr C(OMe)C 6 H 4Z),在大多数情况下,离开小组的离开是限速的。取代基对亲核连接步骤的影响(平均ρ= 0.55)比甲氧基类似物(ρ= 2.03)弱得多。结果表明,(CO)5 Cr C(SMe)C 6 H 4 Z的小ρ值是“正常”的,反映了在过渡态时取代基对部分正电荷和部分负电荷的作用几乎抵消。这些发现提供了证据:(CO)5 Cr C(OMe)C 6 H 4 Z的高ρ值是“异常的”,并且是甲氧基对反应物卡宾络合物的强烈π供体作用的结果。