environment for borylation adjacent to these bonds. They also proved, via DFT
calculations, that borylation or heteroarenes do not occur alpha or ortho to basic
nitrogen moieties probably due to the combination of a higher-energy pathway for
the borylation adjacent to basic nitrogen relative to the borylation at other sites and
the instability of the products from borylation adjacent to basic nitrogen under the
reaction conditions.
Simultaneously to the previous example, Colacot and co-workers developed a
cheaper catalytic system based on Ir(I) modified with 1,10-phenantroline ligand
(Phen). This work is remarkable because the authors studied the effect of preformed
versus in situ formed iridium complexes for C–H borylation of heteroarenes, with a
ligand that is 5 and 13 times cheaper than dtbpy and Me 4 Phen, respectively
[20]. They developed a robust and operationally simple process with relatively
low Ir loading to borylate C–H of heterocycles (Scheme 5). One of the key points
Scheme 4 Iridium-catalyzed CÀH borylation of azaindoles
Scheme 5 Preformed iridium-catalyzed CÀH borylation of N-containing heterocycles
Iridium-Catalyzed Undirected Homogeneous C–H Borylation Reaction
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