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.

Conformational transitions of biopolymers are well-known to be affected by noncovalent interactions with small molecules. We found that synthetic polymers, poly- and oligo(meta-ethynylpyridine)s, are guided to helical structures by uncharged hydrogen-bonding interactions with saccharides enclosed in the inner sphere of the polymers. Circular dichroism (CD) studies revealed that chirality of saccharide was transferred to the helical sense of the polymers. Among the n-octyl pyranosides of naturally important hexoses, beta-glucoside induced CDs most effectively. Size-regulated 18-mer and longer oligomers also showed the induced CDs similar to those for the polymers. Furthermore, native monosaccharides were extracted into less polar organic solvent with the help of the polymers, inducing similar CD signals.

The dichlorodioxomolybdenum­(VI) complex (MoO2Cl2) is an efficient and low-cost homogeneous catalyst for a variety of organic reactions, but its activity usually decreases after immobilization on a solid support. This report describes the synthesis of heterogeneous Mo complex catalysts using a bipyridine-periodic mesoporous organosilica (BPy-PMO) as a solid chelating ligand and MoO2Cl2 as a precursor, and their catalysis in the epoxidation of olefins with tert-butyl hydroperoxide (TBHP). The MoO2Cl­(OH) complex could be immobilized on trimethylsilylated BPy-PMO (BPy-PMO-TMS), which was confirmed by Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray absorption fine-structure analysis. The Mo complex immobilized on BPy-PMO-TMS exhibited greater catalytic activity for the epoxidation of cis-cyclooctene compared with conventional heterogeneous Mo complex catalysts using mesoporous silica, polystyrene, and naked BPy-PMO as supports. A large amount (up to 0.72 mmol g–1) of the Mo complex could be loaded on BPy-PMO-TMS, which resulted in 37% of the exposed bipyridine ligands on the surface forming Mo complexes. The turnover frequency relative to Mo was nearly constant, even with a high density of Mo complex on the pore surface. The Mo-BPy-PMO-TMS catalyst exhibited a solvent effect on the catalysis, and the presence of water in the reaction medium was detrimental for the catalysis. Under anhydrous conditions, Mo-BPy-PMO-TMS showed good catalytic activity for at least three reuse cycles in the epoxidation of cis-cyclooctene. A variety of olefins including aliphatic and aromatic olefins were successfully oxidized by Mo-BPy-PMO-TMS to give the desired epoxides in high yield.

Periodic mesoporous organosilica with densely packed pyridine units within the framework and crystal-like molecular-scale periodicity was synthesized. The framework pyridines were chemically active and fully accessible for protonation and Cu(2+) adsorption.