Larock indole synthesis using palladium complexes immobilized onto mesoporous silica

Heterogeneous palladium catalysts were prepared by covalent immobilization of palladium (II) complexes of the general formula PdCl2L2 (L = P, CN) onto SBA-15 silica using a post-synthetic method. The state of the hybrid materials was characterized using a wide variety of molecular and solid-state techniques. In general, all the palladium modified solids exhibited highly ordered mesostructures while keeping the integrity of the parent molecular precursors. The catalytic performances of the materials were evaluated in the heteroannulation of 2-iodoaniline and 2-bromoaniline with triethyl(phenylethynyl)silane which showed high activities and selectivities with isolated yields in the range of 80–85%. Despite a decrease in the initial activity, quantitative conversion of iodoaniline to the expected product was observed over multiple recyclings, making these materials particularly efficient for such applications. The catalytic process was shown to be homogeneous in nature, the solid apparently serving as a “reservoir” for the metal between cycles.

Figure optionsDownload high-quality image (35 K)Download as PowerPoint slideResearch highlights▶ Palladium (II) complexes covalently immobilized onto SBA-15 silica were prepared using a post-synthetic procedure. ▶ The integrity of the parent molecular precursors in highly ordered mesostructured solids was confirmed. ▶ The materials exhibit high performance for the heteroannulation of 2-iodoaniline and 2-bromoaniline with triethyl(phenylethynyl)silane over multiple recyclings. ▶ The catalysis was shown to be homogeneous, the solid apparently serving mainly as a metal reservoir.