A unique coplanar multi-center bonding network in doubly acetylide-bridged binuclear zirconocene complexes: A density functional theory study
- 作者：Shuqiang Niu ; Agnes Derecskei-Kovacs ; Michael B. Hall
- 关键词：Density functional theory ; C– ; C coupling ; Coplanar multi-center bonding ; Alkynyl migration mechanism ; Isomerization transition state
- 刊名：Journal of Organometallic Chemistry
- 出版年：2007
- 期刊代码：64_0022328x
- 类别：ch
- 出版时间：1 October 2007
- 卷：692
- 期：21
- 页码：4760-4767
- 文件大小：762 K
摘要
A unique π-conjugative interaction pattern was experimentally revealed in the doubly acetylide-bridged binuclear group 4 metallocene complexes, which was involved in C–C coupling/cleavage reactions of acetylides and σ-alkynyl migrations. To elucidate how this multi-center bonding network affects the structural and reaction properties of these complexes, density functional theory (DFT) calculations and molecular orbital (MO) analysis were carried out on the electronic structure and σ-alkynyl migration mechanisms of the doubly acetylide-bridged binuclear Zr complexes, (L2Zr)2(μ-C
CH)2 (L = Cp, Cl). The B3LYP calculations suggested that the doubly [σ,π] acetylide-bridged complex C2h-(L2Zr)2(μ-CCH)2 was produced by the reaction of L2Zr(CCH)2 with L2Zr through a C2v-(L2Zr)2(μ-CCH)2 intermediate followed by an isomerization process. In particular, the isomerization of C2h- or C2v-(L2Zr)2(μ-CCH)2 is almost thermoneutral through a low barrier of 15.3–17.0 kcal/mol. The MO Walsh diagram revealed that the two isomers have a very similar six-center-six-electron bonding network. The coplanar π-conjunctive interaction by the electron donating and back-donating interactions between the metal centers and acetylide ligands significantly stabilizes the doubly acetylide-bridged binuclear group 4 metallocene complexes and the isomerization transition state.