Indol-2-ylidene (IdY): Ambiphilic N-Heterocyclic Carbene Derived from Indole*.

The synthesis of ambiphilic N-heterocyclic carbene ligand, indol-2-ylidene (IdY, A), is described. A series of indolenium precursors (2 a-f) were prepared on a gram scale in good yields. Trapping experiments with elemental selenium, [RhCl(cod)]2 and CuCl provided the expected carbene adducts. Further computational and spectroscopic studies supported the ambiphilicity of IdY, which lies between cyclic (alkyl)(amino)carbenes (CAAC-5) and cyclic (amino)(aryl)carbene (CAArC). The copper complexes (6) show high percent buried volume (% Vbur = 58.1) and allow for carboboration of terminal alkynes within 30 minutes in a demonstration of synthetic utility with good yields and high regioselectivity.