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

Abstract

We report an iron system, Cp*Fe(1,2-R 2 PC 6 H 4 X), which controls the Markovnikov and anti-Markovnikov hydrostannation of alkynes by tuning the ionic metal−heteroatom bonds (Fe−X) reactivity. The sequential addition of nBu 3 SnH 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 βvinylstannanes. 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.

Bioinspired Iron-Catalyzed Dehydration of Aldoximes to Nitriles: A General N–O Redox-Cleavage Method

“…Although these iron­(II) nitrile compounds feature an 18-electron configuration, they are paramagnetic in benzene solution. As measured by the Evans method, the effective magnetic moments of 2a – 2c are in the range of 2.80–2.81, consistent with the values reported previously for intermediate-spin iron­(II) complexes. ,,− …”

“…The HRMS was performed on a Q-TOF mass spectrometer, Bruker impact II Mass Spectrometer Q-TOF6510. Cp*Fe­(1,2-PCy 2 C 6 H 4 O)­( 1 ), the oxime substrates including 3b – 3ab , 3af – 3aj , 3am – 3at , d -3b , and 1,2-benzisoxazoles 5a – 5k were prepared according to the reported procedures.…”

“…We are interested in half-sandwich iron complexes of the Cp*Fe­(1,2-R 2 PC 6 H 4 X) (X = S – , O – , or HN – ) type that have an ionic metal–heteroatom (M–X) bond . Such coordinatively unsaturated iron­(II) complexes adopting an intermediate-spin (S = 1) state usually show intriguing reactivities in bond activation and catalysis. , Herein, we report a general iron-catalyzed dehydration system that achieves selective transformation of various aliphatic and aromatic aldoximes to nitriles by direct release of H 2 O at room temperature (Figure b). The reactions are based on catalytic homolytic cleavage of the N–O bond in oximes by the iron complex Cp*Fe­(1,2-Cy 2 PC 6 H 4 O) ( 1 ).…”

A Parent Iron Amido Complex in Catalysis of Ammonia Oxidation

“…Our previously reported half-sandwich iron­(II) complex, Cp*Fe­(1,2-Ph 2 PC 6 H 4 NH) ( 1 ) bearing a phosphinoamido ligand, is stable toward NH 3 . Once oxidized, however, the iron complex binds NH 3 to afford a ferric ammine complex, Fe­(III)NH 3 .…”

“…Of note, the iron oxidation states are denoted by their formal oxidation states, and the assignments of the physical oxidation states are deferred in the Electronic Structure Analyses section. 45 bearing a phosphinoamido ligand, is stable toward NH 3 . Once oxidized, however, the iron complex binds NH 3 to afford a ferric ammine complex, Fe(III)NH 3 .…”