Cyclic (Alkyl)amino Carbene Based Iron Catalyst for Regioselective Dimerization of Terminal Arylalkynes

[(cAAC)­Fe­(CO)4] (1) catalyzed head-to-head dimerization of terminal arylalkynes toward conjugated enynes in very high yield and high E selectivity (up to 84:16 E:Z). The protocol can be performed under extremely low catalyst loading down to 0.01 mol %, resulting in a high TON of 6500. A mechanistic pathway for arylalkyne dimerization has been proposed on the basis of a well-defined catalyst, an isolable intermediate, and quantum chemical calculations.