Fe-Promoted C–F Activation of Aryl Fluorides Enables Heck-Type Coupling with Alkenes and One-Pot Synthesis of Indenes

Abstract

Metal-mediated aryl fluoride activation not only presents challenges because of the thermodynamically robust C–F bond but also provides opportunities to develop C–C coupling reactions with this unconventional electrophile. Here, we report that the metallanucleophile, K[CpFe(CO)2] (KFp), is readily arylated by aryl fluorides to provide CpFe(CO)2Ar (FpAr) complexes under ambient conditions in the absence of any catalyst, contrary to previous literature reports. This C–F activation likely proceeds by a SNAr mechanism rather than the more common oxidative addition pathway for metal-mediated C–F cleavage. Facile access to FpAr derivatives has enabled further development of Fe-promoted coupling reactions of aryl fluorides with alkenes and alkynes. Under stoichiometric Fe conditions, Heck-type coupling reactions with aryl fluoride electrophiles are reported herein. Various aryl fluorides were found to couple with olefins to provide E-alkene products; aliphatic derivatives unexpectedly underwent reduction to 1,2-disubstituted ethane products to varying extents. Aryl fluorides were also found to couple with 5-decyne to yield indene derivatives in a one-pot manner; indenone and indanone products were also observed in selected cases. A mechanistic investigation to identify the apparently potent hydride donor generated under these conditions was conducted, leading to a mechanistic hypothesis involving the intermediacy of metal carbonyl-capped, triple-decker ferrocene compounds as reductants. Despite the involvement of these di-iron intermediates limiting stoichiometric product yields, the observed C–C coupling reactions expand the limits of organofluorine chemistry.

Photochemical H2 activation by an Zn–Fe heterometallic: a mechanistic investigation

“…Formation in a 1 : 1 ratio conserves the reaction stoichiometry. Generation of 3a could be considered to derive from: (i) 1a reacting with [Fe(η 5 -C 5 H 5 )(CO) 2 ] 2 to form 2a and [Fe(η 5 -C 5 H 5 )(H)(CO) 2 ] 26–28 as a transient intermediate which is then trapped by a second equiv. of 1a to form 3a or (ii) addition of in situ generated H 2 across the Zn–Fe bond of 2a under photochemical conditions.…”

Activation of robust bonds by carbonyl complexes of Mn, Fe and Co

“…Earlier this year, in 2023, in line with data shown above, our study featured a new method for the synthesis of aryliron( ii ) carbonyls 16 via reaction of KFp with monofluorobenzenes 15 with (-M)-electron-withdrawing groups and electron-poor monofluoropyridines. 65 Still, electron-rich monofluorides remained unreactive under studied conditions (Scheme 3a). It is interesting to note that previously this reaction was considered impossible by some based on preliminary studies of reduction of electron-deficient bromo and iodobenzenes with KFp.…”