Recyclable Silica-Supported Iridium Bipyridine Catalyst for Aromatic C H Borylation

A mesoporous silica (SBA-15)-supported bipyridine iridium complex is prepared by grafting of bipyridine onto the silica support, followed by complexation of an iridium(I) precursor in the presence of HBpin and cyclooctene. Structural analyses by X-ray powder diffraction, nitrogen physisorption, FT-IR, and solid-state NMR spectroscopy demonstrate that the 3-dimensional, hexagonal pore structure of SBA-15 is maintained after the immobilization. In particular, as a heterogeneous catalyst, this silica-supported iridium complex shows moderate to good catalytic activity in the aromatic C H borylation of a variety of substrates. More importantly, the heterogeneous catalyst is recovered easily and reused repeatedly by simple washing without chemical treatment and exhibits good recycling performance with a modest decrease in the catalytic rate, showing good potential for increasing the overall turnover number of this synthetically useful catalyst.