Iron-Catalyzed Regiodivergent Hydrostannation of Alkynes: Intermediacy of Fe(IV)–H versus Fe(II)–Vinylidene

We report an iron system, Cp*Fe(1,2-R2PC6H4X), which controls the Markovnikov and anti-Markovnikov hydrostannation of alkynes by tuning the ionic metal–heteroatom bonds (Fe–X) reactivity. The sequential addition of nBu3SnH to the iron–amido catalyst (1, X = HN–, R = Ph) affords a distannyl Fe(IV)–H species responsible for syn-addition of the Sn–H bond across the C≡C bond to produce branched α-vinylstannanes. Activation of the C(sp)–H bond of alkynes by an iron–aryloxide catalyst (2, X = O–, R = Cy) affords an iron(II) vinylidene intermediate, allowing for gem-addition of the Sn–H to the terminal-carbon producing β-vinylstannanes. These catalytic reactions exhibit excellent regioselectivity and broad functional group compatibility and enable the large-scale synthesis of diverse vinylstannanes. Many new reactions have been established based on such a synthetic Fe–X platform to demonstrate that the initial step of the catalysis is conveniently controlled by the activation of either the tin hydride or the alkyne substrate.