C–H borylation catalysis of heteroaromatics by a rhenium boryl polyhydride

Donnelly, Liam J. and Faber, Teresa and Morrison, Carole A. and Nichol, Gary S. and Thomas, Stephen P. and Love, Jason B. (2021) C–H borylation catalysis of heteroaromatics by a rhenium boryl polyhydride. ACS Catalysis, 11 (12). 7394–7400. ISSN 2155-5435 (https://doi.org/10.1021/acscatal.1c00869)

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Transition metal complexes bearing metal–boron bonds are of particular relevance to catalytic C–H borylation reactions, with iridium polyboryl and polyhydrido-boryl complexes the current benchmark catalysts for these transformations. Herein, we demonstrate that polyhydride boryl phosphine rhenium complexes are accessible and catalyze the C–H borylation of heteroaromatic substrates. Reaction of [K(DME)(18-c-6)][ReH4(Bpin)(η2-HBpin)(κ2-H2Bpin)] 1 with 1,3-bis(diphenylphosphino)propane (dppp) produced [K(18-c-6)][ReH4(η2-HBpin)(dppp)] 2 through substitution of two equivalents of HBpin, and protonation of 2 formed the neutral complex [ReH6(Bpin)(dppp)] 3. Combined X-ray crystallographic and DFT studies show that 2 is best described as a σ-borane complex, whereas 3 is a boryl complex. Significantly, the boryl complex 3 acted as a catalyst for the C(sp2)–H borylation of a variety of heteroarenes (14 examples including furan, thiophene, pyrrole and indole derivatives) and displayed similar reactivity to the iridium analogues.