Catalysis of Organic..

Durán Pachón and Rothenberg 503the coupling reaction could occur on the cathode surface. Electron transfer from aPd 0 atom on the cathode surface to PhI would give a [PhI] –• radical anion, that wouldthen dissociate to Ph • and I – (11). The constant supply of electrons to the cathodewould ensure the electron transfer. However, we did not observe any reaction in thiscase (nor were any Pd nanoparticles formed). Thus, we conclude that palladiumnanoparticles are necessary for catalysing the homocoupling of aryl halides.Table 1 Ullmann homocoupling of various haloaryls. aEntryArylhalideBiaryl productConversion(%) b Yield(%) b TON c Time(h)1I99 80 816 8INO 2299 82 811 8O 2 NO 2 N3Br99 75 701 14NO 2Br474 61 540 20O 2 NO 2 NBrOCH 35H 3 CO80 65 550 24H 3 COClNO 265 4 32 24O 2 NO 2 Na Reaction conditions: 20 mmol aryl halide, 50 mL [omim] + [BF 4 ] – , 25 ºC.b Based on GC analysis, corrected for the presence of an internal standard.cBased on the difference in weight in the Pd anode before and after the reaction.