Computational understanding of catalyst-controlled borylation of fluoroarenes: directed 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)/PNP and Ir(iii)/dtbpy (4,4-di--butyl bipyridine). The calculation results indicate that for the Co(i)/PNP catalytic system, the undirected pathway is 2.9 kcal mol more favoured over the directed pathway leading to -to-fluorine selectivity. In contrast, for the Ir(iii)/dtbpy catalytic system, the directed pathway is 1.2 kcal mol more favoured over the undirected pathway bringing about -to-silyl selectivity. For Co(i)/PNP catalyzed borylation, the undirected pathway which involves steps of -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 -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 (o-to-fluorine selectivity) for Co(i)/PNP catalyzed borylation and the favourable directed pathway (-to-silyl selectivity) for Ir(iii)/dtbpy catalyzed borylation could explain well the experimentally observed -to-fluorine borylation of hydrosilyl substituted fluoroarenes with cobalt catalyst (J. V. Obligacion, M. J. Bezdek and P. J. Chirik, , 2017, , 2825-2832) and -to-silyl selectivity with iridium catalyst (T. A. Boebel and J. F. Hartwig, , 2008, , 7534-7535).