Z -selective dimerization of terminal alkynes by a (PNNP)Fe II complex.

A tetradentate bis(amido)bis(phosphine) Fe II complex, (PNNP)Fe, is shown to activate the terminal C-H bond of aryl alkynes across its Fe-N amide bonds. (PNNP)Fe is also shown to catalytically dimerize terminal aryl alkynes to produce 1,3-enynes with Z  :  E ratios as high as 96 : 4 with yields up to 95% and loadings as low as 1 mol% at 30 °C in 2 h. A plausible metal-ligand cooperative mechanism invoking a vinylidene intermediate is proposed.