Suzuki reaction catalysed by a PCsp3P pincer Pd(II) complex: Evidence for a mechanism involving molecular species

{Cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexyl}palladium(II)trifluoroacetate (1) acts as a precatalyst for the Suzuki reaction of aryl halides with phenylboronic acid in the absence or presence of mercury to give the product in modest to reasonably good yields. The reaction was monitored by 31P- and 1H NMR spectroscopy in a stepwise fashion, concluding that complex 1 reacts with activated boronic acids in the first reaction step to yield the corresponding phenyl complex 2. Complex 2 thereafter generates the Suzuki cross-coupling product upon addition of aryl halide. This shows that (PCP)Pd complexes, in addition to the previously demonstrated Pd(0)/Pd(II) mechanism, can mediate cross-coupling reactions using molecular species in a non-zero oxidation state.

Based on a mechanistic investigation of the Suzuki reaction catalysed by an aliphatic PCP palladium pincer complex an alternative parallel reaction mechanism based on soluble palladium(II) species only is proposed.Figure optionsDownload as PowerPoint slide