A Solid Chelating Ligand: Periodic Mesoporous Organosilica Containing 2,2′-Bipyridine within the Pore Walls

Abstract

Synthesis of a solid chelating ligand for the formation of efficient heterogeneous catalysts is highly desired in the fields of organic transformation and solar energy conversion. Here, we report the surfactant-directed self-assembly of a novel periodic mesoporous organosilica (PMO) containing 2,2'-bipyridine (bpy) ligands within the framework (BPy-PMO) from a newly synthesized organosilane precursor [(i-PrO)3Si-C10H6N2-Si(Oi-Pr)3] without addition of any other silane precursors. BPy-PMO had a unique pore-wall structure in which bipyridine groups were densely and regularly packed and exposed on the surface. The high coordination ability to metals was also preserved. Various bipyridine-based metal complexes were prepared using BPy-PMO as a solid chelating ligand such as Ru(bpy)2(BPy-PMO), Ir(ppy)2(BPy-PMO) (ppy = 2-phenylpyridine), Ir(cod)(OMe)(BPy-PMO) (cod = 1,5-cyclooctadiene), Re(CO)3Cl(BPy-PMO), and Pd(OAc)2(BPy-PMO). BPy-PMO showed excellent ligand properties for heterogeneous Ir-catalyzed direct C-H borylation of arenes, resulting in superior activity, durability, and recyclability to the homogeneous analogous Ir catalyst. An efficient photocatalytic hydrogen evolution system was also constructed by integration of a Ru-complex as a photosensitizer and platinum as a catalyst on the pore surface of BPy-PMO without any electron relay molecules. These results demonstrate the great potential of BPy-PMO as a solid chelating ligand and a useful integration platform for construction of efficient molecular-based heterogeneous catalysis systems.