developed a detailed study about the effect of the electronic properties of
phenanthroline ligands on the electron-donating ability of these ligands and on the
rates for cleavage of CÀH bonds by iridiumÀtrisboryl complexes that catalyze the
borylation of CÀH bonds [18].
Hartwig and co-workers developed in 2014 the iridium-catalyzed CÀH
borylation of several heteroarenes containing multiple heteroatoms, such as
benzoxazoles (Scheme 2), pyrimidines, and unprotected benzimidazoles (Scheme
3), pyrazoles, and azaindoles (Scheme 4), by the combination of an iridium
(I) precursor [Ir(μ-OMe)(COD)] 2 /Me 4 Phen and B 2 pin 2 [19].
In this work, the authors led to the development of powerful rules for predicting
the regioselectivity of borylation of heteroarenes showing that borylation occurs
distal to NÀH bonds due to rapid NÀH borylation, creating an unfavorable steric
Scheme 2 Iridium-catalyzed CÀH borylation of benzoxazoles
Scheme 3 Iridium-catalyzed CÀH borylation of benzimidazoles
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E. Fernández