α‑Dicationic Chelating Phosphines: Synthesis and Application to the Hydroarylation of Dienes

A series
of new P^P-chelating ligands constituted by a dicationic
−[P­(H2Im)2]+2 unit (H2Im = 1,3-dimethyl-4,5-dihydroimidazol-2-ylidene) and a −PPh2 group connected through structurally different backbones
have been synthesized. Evaluation of their reactivity toward different
metal centers provides evidence that the dicationic fragment, otherwise
reluctant to coordinate metals, readily participates in the formation
of chelates when embedded into such a scaffold. Moreover, it significantly
enhances the Lewis acidity of the metals to which it coordinates.
This property has been used to develop a Rh catalyst that efficiently
triggers the hydroarylation of dienes with electron-rich aromatic
molecules. Kinetic studies and deuterium-labeling experiments, as
well as density functional theory calculations, were performed in
order to rationalize these findings.

一系列由双阳离子−[P(H₂Im)₂]²⁺单元（其中H₂Im为1,3-二甲基-4,5-二氢咪唑-2-亚基，英文全称为1,3-dimethyl-4,5-dihydroimidazol-2-ylidene）与−PPh₂基团通过结构各异的骨架连接而成的新型P^P螯合配体已成功合成。对其与不同金属中心的反应性开展评估后证实，原本难以与金属配位的该双阳离子片段，在嵌入此类骨架后可顺利参与螯合物的形成。此外，该片段可显著提升其所配位金属的路易斯酸性。依托这一特性开发出的铑（Rh）催化剂，可高效催化富电子芳香分子与二烯烃的氢芳基化反应。为阐明上述实验结果的内在机理，本研究开展了动力学研究、氘标记实验以及密度泛函理论（density functional theory, DFT）计算。