Ionic liquids as reaction media for palladium-catalysed cross-coupling of aryldiazonium tetrafluoroborates with potassium organotrifluoroborates

The system comprising a palladium complex in a 1-butyl-3-methylimidazolium tetrafluoroborate/methanol mixture efficiently catalyses the cross-coupling reaction between p-tolyl-diazonium tetrafluoroborate and potassium phenyltrifluoro-borate at room temperature. The presence of methanol (or water) in the reaction mixture is necessary in order to achieve quantitative conversions, due to its scavenging behaviour towards the BF3 formed during the reaction. Yields higher than 90% were obtained using Pd-2(dba)(3) or the azapalladacycle 10 as the palladium source. With the latter complex a turnover frequency of about 6000 h(-1) was attained in the coupling of aryldiazonium tetrafluoroborates with potassium vinyltrifluoroborate. Recycling of the catalytic solution could be performed provided that a slight excess of diazonium salt was used in the first run. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)