Electron-poor three-center systems

In the last ten years, it has been shown that although bis(amino)carbenes such as 25 do not behave as classical transient singlet carbenes (no cyclopropanation reaction, no 1,2-shift, no C-H insertion...), they are wonderful ligands for transition metals which have very high catalytic activities. [27] Their three center four k electron system makes them strong a-donor and poor Ji-attractor. In other words, they constitute a new class of Lewis base. Despites these facts, in the last two highlights of Angew. Chem. [28] devoted to stable carbenes, only bis(amino)carbenes were considered, without any mention of our work This prompted us, to work harder and harder to demonstrate that our carbene 17 was a true carbene, and that it was even possible to obtain other types of stable carbenes, which are closer to the transient species. 

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