Endo-Selective Iron Catalysts for Intramolecular Alkyne Hydrofunctionalization
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Metal-ligand cooperative iron complexes of the type [Fe(Cp*)(PR2NPh2)(MeCN)]PF6 (R = Cy, Ph) were synthesized and characterized. Both derivatives were active toward the intramolecular hydroamination of 2-ethynylaniline and hydroalkoxylation of 2-ethynylbenzyl alcohol. In the latter case, only the six-membered endo heterocycle isochromene was observed, which suggests that the alkyne is activated by a vinylidene mechanism. The reaction of [Fe(Cp*)(PCy2NPh2)(MeCN)]PF6 with phenylacetylene indeed afforded a complex that was characterized as a vinylidene, which implicates an analogous intermediate in the hydrofunctionalization mechanism.