Csp2–H/F bond activation and borylation with low valent iron

Abstract

Reduction of [K2{(tBupyrr2pyr)Fe}2(mu-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 Csp2–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.