Efficient cross-coupling of secondary alkyltrifluoroborates with aryl chlorides--reaction discovery using parallel microscale experimentation.

Microscale parallel experimentation was used to discover three catalyst systems capable of coupling secondary organotrifluoroborates with sterically and electronically demanding aryl chlorides and bromides. The ensuing results represent the first comprehensive study of alkylboron coupling to aryl chlorides and, in particular, using secondary alkylboron partners. A ligand-dependent beta-hydride elimination/reinsertion mechanism was implicated in the cross-coupling of more hindered substrates, leading to isomeric mixtures of coupled products in some cases.