Computational understanding of catalyst-controlled borylation of fluoroarenes: directed vs. undirected pathway.

In this work, density functional theory (DFT) calculations are performed to understand the origin of the regioselective C-H borylation of aromatics catalyzed by Co(i)/iPrPNP and Ir(iii)/dtbpy (4,4-di-tert-butyl bipyridine). The calculation results indicate that for the Co(i)/iPrPNP catalytic system, the undirected pathway is 2.9 kcal mol-1 more favoured over the directed pathway leading to ortho-to-fluorine selectivity. In contrast, for the Ir(iii)/dtbpy catalytic system, the directed pathway is 1.2 kcal mol-1 more favoured over the undirected pathway bringing about ortho-to-silyl selectivity. For Co(i)/iPrPNP catalyzed borylation, the undirected pathway which involves steps of ortho-to-fluorine C-H oxidative addition, C-B reductive elimination, B-B oxidative addition, and B-H reductive elimination is favorable due to the electron deficient character of the ortho-to-fluorine C-H bond. For Ir(iii)/dtbpy catalyzed borylation, the directed pathway consisting of Si-H oxidative addition, B-H reductive elimination, C-H oxidative addition, B-B oxidative addition, C-B reductive elimination, Si-H reductive elimination is favored over the undirected pathway attributed to the directing effect of the hydrosilyl group. The favourable undirected pathway (ortho-to-fluorine selectivity) for Co(i)/iPrPNP catalyzed borylation and the favourable directed pathway (ortho-to-silyl selectivity) for Ir(iii)/dtbpy catalyzed borylation could explain well the experimentally observed ortho-to-fluorine borylation of hydrosilyl substituted fluoroarenes with cobalt catalyst (J. V. Obligacion, M. J. Bezdek and P. J. Chirik, J. Am. Chem. Soc., 2017, 139, 2825-2832) and ortho-to-silyl selectivity with iridium catalyst (T. A. Boebel and J. F. Hartwig, J. Am. Chem. Soc., 2008, 130, 7534-7535).