Immobilization of a Molybdenum Complex on Bipyridine-Based Periodic Mesoporous Organosilica and Its Catalytic Activity for Epoxidation of Olefins

Abstract

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.

Microreactor Coated with Mesoporous Organosilica Thin Film as a Support for Metal Complex Catalysts

“…In fact, because this type of Mo catalysts is noticeably sensitive to the environment, even a small amount of water can deactivate Mo catalysts. [6] Even after the dehydration using molecular sieves 4A, a small amount of water remained in the reactant solution. Furthermore, low concentration of Mo was detected in the effluent (less than 0.4 ppm) although it is near the detection limit of our ICP measurements.…”

“…In addition, the catalytic activity of Mo complexes in DE solvent is greater than that in decane solvent, which is in good agreement with the previous study. [6] However, the difference between TOF val- Table 1. Catalytic activity of MoO 2 Cl 2 inside the microreactor.…”

“…[5b,5c,6,7] Moreover, the leaching of metal species from BPy-PMO is significantly small, compared to other immobilization methods. [6] Hence, BPy-PMO exhibited many attractive features for application to a continuous flow reaction. Herein, we develop a continuous flow reactor with a BPy-PMO catalyst layer to perform heterogeneous catalytic reaction using transition metal complexes.…”

Single‐Site Molybdenum Catalyst for the Synthesis of Fumarate

“…Molybdenum based catalysts are the best and versatile catalysts of many industrially important reactions, such as polymerization reactions, olefin epoxidation and olefin metathesis . Recently, inorganic Mo‐based catalysts and a few of organic Mo complex catalysts have been explored to catalyze didehydroxylation reactions of polyols .…”

“…Among various deoxygenation reactions, for instance high-temperature pyrolysis, [4] hydrodeoxygenation, [5] hydroge-nolysis reactions [6] and acid-catalyzed dehydration, [7] the didehydroxylation reactions can efficiently remove two adjacent hydroxyl groups of polyols in one-step by converting vicinal diols into alkenes. [8] Molybdenum based catalysts are the best and versatile catalysts of many industrially important reactions, such as polymerization reactions, [9] olefin epoxidation [10] and olefin metathesis. [11] Recently, inorganic Mo-based catalysts and a few of organic Mo complex catalysts have been explored to catalyze didehydroxylation reactions of polyols.…”