Hyperdistorted Tungsten Allyl Complexes and Their Stereoselective Deprotonation to Form Dihapto-Coordinated Dienes

Several π-allyl complexes of {TpW(NO)(PMe3)} are investigated as possible sources of η2-diene complexes. In order to prepare the diene complex as a single diastereomer, the allyl complex must undergo deprotonation stereoselectively. Allyl complexes of this tungsten system are highly distorted, with the difference between the W−C bond lengths for the two allyl termini being as much as 0.69 Å. DFT calculations and several crystal structures are presented that collectively suggest that one terminus, C1, distal to the PMe3 group, tends toward an sp2 carbocation. Consistent with this interpretation, deprotonation preferentially occurs at a carbon adjacent to this allyl terminus for six-membered rings. However, in the presence of base the five-membered cyclic analogue [TpW(NO)(PMe3)(C5H7)]+ fails to form either isomer of the corresponding η2-diene complex.

本研究针对{TpW(NO)(PMe3)}的多款π-烯丙基配合物 (π-allyl complexes) 展开探究，考察其作为η²-二烯配合物 (η²-diene complexes) 潜在前驱体的可行性。为获得单一非对映异构体的二烯配合物，该类烯丙基配合物需经历立体选择性脱质子过程。该钨体系的烯丙基配合物存在显著结构畸变，两个烯丙基端基的W−C键长差值最高可达0.69埃（Å）。本文结合密度泛函理论 (DFT, Density Functional Theory) 计算与多组晶体结构解析结果，综合证实：其中远离PMe3配体的端基C1更倾向于呈现sp2杂化碳正离子的结构特征。该结论与实验观测高度吻合：对于六元环体系，脱质子反应优先在该烯丙基端基相邻的碳原子处发生。然而，在碱存在的条件下，五元环环状类似物[TpW(NO)(PMe3)(C5H7)]+无法生成对应η²-二烯配合物的任意一种异构体。