Highly Electrophilic Olefin Polymerization Catalysts. Quantitative Reaction Coordinates for Fluoroarylborane/Alumoxane Methide Abstraction and Ion-Pair Reorganization in Group 4 Metallocene and “Constrained Geometry” Catalysts
作者:Paul A. Deck、Colin L. Beswick、Tobin J. Marks
DOI:10.1021/ja972912f
日期:1998.3.1
Reaction enthalpies of group4metallocenes having the general formula L2M(CH3)2 (L = Cp, 1,2-Me2Cp, Me5Cp; L2 = Me2Si(Me4Cp)(tBuN); M = Ti, Zr, and Hf) with the strong organo-Lewis acid B(C6F5)3 were measured using batch titration calorimetry in toluene. Methideabstraction to form the corresponding L2MCH3+CH3B(C6F5)3- contact ion pairs is highly exothermic in all cases. Exothermicity increases with
具有通式 L2M(CH3)2 (L = Cp, 1,2-Me2Cp, Me5Cp; L2 = Me2Si(Me4Cp)(tBuN); M = Ti、Zr 和 Hf) 的第 4 族金属茂的反应焓与强有机路易斯酸 B(C6F5)3 在甲苯中使用分批滴定量热法测量。在所有情况下,形成相应的 L2MCH3+CH3B(C6F5)3- 接触离子对的甲基化物提取都是高度放热的。放热性随着 Cp 甲基取代基的增加而增加:对于 M = Zr,ΔH = -23.1(3)、-24.3(4) 和 -36.7(5) kcal mol-1,分别为 L = Cp、Me2Cp 和 Me5Cp。对于 M = Hf 和 L = 1,2-Me2Cp,ΔH = -20.8(5) kcal mol-1。“受限几何”配合物 (L2 = Me2Si(Me4Cp)(tBuN)) 表现出类似的放热性,对于 M = Ti,ΔH = -22.6(2)、-23