Csp2–H/F bond activation and borylation with iron

Abstract

Reduction of [K₂{(^tBupyrr₂pyr)Fe}₂(μ-N₂)] (1) with two equiv. of KC₈ in the presence of crown-ether 18-C-6 yields the N₂ adduct [{K(18-C-6)}₂(^tBupyrr₂pyr)Fe(N₂)] (2). Complex 2 heterolytically splits the C_sp²–H bond of benzene to form [{K(18-C-6)}(^tBupyrr₂pyr)Fe(C₆H₅)] (3), whereby usage of a diboron B₂pin₂ promotes hydride elimination to form the salt [K(18-C-6)HB₂Pin₂] (4). Similarly, 3 can also be formed by cleavage of the C–F bond of fluorobenzene. Reaction of 3 with ClBcat yields [K(18-C-6)(thf)₂][(^tBupyrr₂pyr)FeCl] (5) and PhBcat and the former can be reduced to 2 to complete a synthetic cycle for heterolytic benzene C–H activation and borylation.