Selective Dehydrogenative Mono- or Diborylation of Styrenes by Supported Copper Catalysts

The selective dehydrogenative borylation of alkenes is an attractive method for synthesizing useful borylalkenes. However, very few catalytic systems have been reported that fulfill this objective. All the reported examples are homogeneous catalysts with special ligands requiring the usage of bases. This study describes the heterogeneously catalyzed dehydrogenative borylation by supported copper hydroxide catalysts (Cu(OH)x/support). In the presence of Cu(OH)x/support and suitable ketones, the dehydrogenative borylation of styrenes with bis(pinacolato)diboron efficiently proceeded to selectively afford the corresponding β-monoboryl- or β,β-diborylstyrenes. The observed catalysis was truly heterogeneous, and the catalysts could be reused several times, though their catalytic performance gradually declined.