The borylation of arenes leads to the formation of synthetically versatile products from unactivated arene reagents. We report that Ir(I) precursors in conjunction with bipyridine ligands catalyze in high yields the borylation of arenes under mild conditions. These reactions encompase arenes bearing both electron-withdrawing and electron-donating substituents. The temperatures required for the transformation are much lower than those previously reported for direct arene borylation. The combination of [Ir(COE)2Cl]2 and (4,4-di-t-butyl)bipyridine even allows for reaction at room temperature. The same catalyst system at 100 degrees C provides remarkably high turnover numbers for a hydrocarbon functionalization process. Mechanistic studies show that the reactions involve uncommon, Ir(II) tris-boryl complexes. An example of this type of complex ligated by di-t-butylbipyridine was isolated and structurally characterized. It reacted rapidly at room temperature to produce aryl boronate esters in high yields.

-The cross-coupling reaction of bis(pinacolato)diboron with chloroarenes to yield pinacol arylboronates was carried out in 1,4-dioxane at 80 °C in the presence of KOAc (1.5 equivs) and Pd(dba) 2 /2.4PCy 3 (3-6 mol%). The catalyst was also effective to carry out analogous coupling with aryl bromides or triflates under milder conditions than those of the previous procedures catalyzed by PdCl 2 (dppf) in DMSO.

Borylation at the benzylic C–H bond of alkylbenzenes with bis(pinacolato)diboron [(Me4C2O2)B–B(O2C2Me4)] or pinacolborane [(Me4C2O2)B–H] was carried out at 100 °C in the presence of a catalytic amount of 10% Pd/C. The reaction selectively afforded pinacol benzylboronates in good yields directly from various alkylbenzenes.

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.