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.

Increasing attention has been devoted to the direct functionalization of unreactive hydrocarbons by metal-catalyzed reactions because of their wide availability and low cost. [1] A recently developed protocol for hydrocarbon functionalization provides a convenient and direct method for the synthesis of arylboron compounds by the CÀH borylation of arenes by bis(pinacolato)diboron (pin 2 B 2 , [4] [RhCl(PiPr 3 ) 2 (N 2 )], [5] [(Cp*-RhCl 2 ) 2 ], [5] [(h 5 -C 9 H 7 )Ir(cod)]/dppe or dmpe (cod ¼ 1,5cyclooctadiene; dppe ¼ 1,2-bis(diphenylphosphanyl)ethane; dmpe ¼ 1,2-bis(dimethylphosphanyl)ethane), [6] and 1/2[IrCl-(cod)] 2 /2,2'-bipyridine. [7] Among them, iridium(i) complexes generated from [{IrCl(cod)} 2 ] and 2,2'-bipyridine (bpy) exhibited exceptionally high catalyst activity and turnover numbers in neat arene substrate at 80 8C. [7] Moreover, the combination of [IrCl(coe) 2 ] 2 (coe ¼ cyclooctene) and 4,4'-ditert-butyl-2,2'-bipyridine (dtbpy) catalyzed the same reaction at room temperature. [7] We report here the development of catalysts that allow for the first time the direct borylation of arenes or heteroarenes at room temperature in an inert solvent with a stoichiometric ratio of pin 2 B 2 [8] (1) to arene (2) to produce the corresponding arylboronates (3) in high yields (Scheme 1).During subsequent studies of the aromatic CÀH borylation, we found that the effect of varying the anionic ligands (X) on iridium(i) precursors could provide a greater effect on catalyst COMMUNICATIONS 3056

Abstract-TheRegioselective synthesis of bis(boryl)heteroaromatics was also achieved by using an almost equimolar amount of substrates and the diboron.--

The synthesis of 1-alkenylboronic acid pinacol esters via a palladium-catalyzed cross-coupling reaction of bis(pinacolato)diboron (pin(2)B(2), pin = Me(4)C(2)O(2)) with 1-alkenyl halides or triflates was carried out in toluene at 50 degrees C in the presence of KOPh (1.5 equiv) and PdCl(2)(PPh(3))(2)-2Ph(3)P (3 mol %). The borylation of acyclic and cyclic 1-alkenyl bromides and triflates was achieved in high yields with complete retention of configuration of the double bonds. The method was applied to the one-pot synthesis of unsymmetrical 1,3-dienes via the borylation-coupling sequence.

Increasing attention has been devoted to the direct functionalization of unreactive hydrocarbons by metal-catalyzed reactions because of their wide availability and low cost. [1] A recently developed protocol for hydrocarbon functionalization provides a convenient and direct method for the synthesis of arylboron compounds by the CÀH borylation of arenes by bis(pinacolato)diboron (pin 2 B 2 , [4] [RhCl(PiPr 3 ) 2 (N 2 )], [5] [(Cp*-RhCl 2 ) 2 ], [5] [(h 5 -C 9 H 7 )Ir(cod)]/dppe or dmpe (cod ¼ 1,5cyclooctadiene; dppe ¼ 1,2-bis(diphenylphosphanyl)ethane; dmpe ¼ 1,2-bis(dimethylphosphanyl)ethane), [6] and 1/2[IrCl-(cod)] 2 /2,2'-bipyridine. [7] Among them, iridium(i) complexes generated from [{IrCl(cod)} 2 ] and 2,2'-bipyridine (bpy) exhibited exceptionally high catalyst activity and turnover numbers in neat arene substrate at 80 8C. [7] Moreover, the combination of [IrCl(coe) 2 ] 2 (coe ¼ cyclooctene) and 4,4'-ditert-butyl-2,2'-bipyridine (dtbpy) catalyzed the same reaction at room temperature. [7] We report here the development of catalysts that allow for the first time the direct borylation of arenes or heteroarenes at room temperature in an inert solvent with a stoichiometric ratio of pin 2 B 2 [8] (1) to arene (2) to produce the corresponding arylboronates (3) in high yields (Scheme 1).During subsequent studies of the aromatic CÀH borylation, we found that the effect of varying the anionic ligands (X) on iridium(i) precursors could provide a greater effect on catalyst ZUSCHRIFTEN 3182