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Diverse Alkyl-Silyl Cross-Coupling via Homolysis of Unactivated C(sp3)-O Bonds with the Cooperation of Gold Nanoparticles and Amphoteric Zirconium Oxides

Hiroki Miura*, Masafumi Doi, Yuki Yasui, Yosuke Masaki, Hidenori Nishio and Tetsuya Shishido*

*Department of Applied Chemistry for Environment, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan, Email: miura-hirokitmu.ac.jp, shishido-tetsuyatmu.ac.jp

H. Miura, M. Doi, Y. Yasui, Y. Masaki, H. Nishio, T. Shishido, J. Am. Chem. Soc., 2023, 145, 4613-4625.

DOI: 10.1021/jacs.2c12311



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Abstract

Gold nanoparticles supported on ZrO2 efficiently generate alkyl radicals via homolysis of unactivated C(sp3)-O bonds. A subsequent C(sp3)-Si bond formation provides diverse organosilicon compounds. A wide array of esters and ethers participated in the heterogeneous gold-catalyzed silylation by disilanes to give diverse alkyl-, allyl-, benzyl-, and allenyl silanes in high yields.


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proposed mechanism



Preparation of supported Au catalysts by a deposition-precipitation method

Supported Au catalysts (Au/ZrO2, Au/Al2O3, and Au/TiO2) were prepared by a deposition-precipitation method with the use of HAuCl43H2O as an Au precursor. The pH value of an aqueous solution (75 ml) containing 50 mg of HAuCl43H2O was adjusted to 4 by 1 M NaOH solution. After 0.97 g of support was added to the solution, the pH value was re-adjusted to 7 with 1 M NaOH solution. The suspension was stirred at 343 K for 1 h, separated by centrifugation, and then washed three times with deionized water. After the resulting powder was dried at 353 K overnight, calcination in air at 573 K for 1h, followed by reduction in a hydrogen atmosphere at 473 K for 1 h gave supported Au catalysts. The total loading amount of gold was set at 3 wt%.

General procedure for the reaction of alkyl acetates with disilanes over Au/ZrO2 catalyst

A typical reaction procedure is as follows: alkyl acetate (0.30 mmol), hexamethyldisilane (0.9 mmol) and toluene (1.0 mL) were added to a Schlenk tube containing the supported Au catalyst (3 mol% as Au) under an ambient pressure of Ar. The reaction was conducted at a hot stirrer with a cooling block (HHE-19GUSII; KPI). The progress of the reaction was monitored by thin layer chromatography (TLC) and GC analysis. After the ester or disilane was completely consumed, the solid catalyst was removed by passing the mixture through a 0.45 μm polytetrafluoroethylene (PTFE) filter (Millipore Millex LH). The remaining solution was concentrated by rotary evaporation under reduced pressure without heating. The resulting liquid was purified through silica gel column chromatography (a mixture of hexane and AcOEt) to give the product.

General procedure for the reaction of propargy carbonates and disilanes to allenylsilanes over Au/ZrO2 catalyst

A typical reaction procedure is as follows: propargyl carbonate (0.50 mmol), disilane (1.5 mmol) and toluene (1.0 mL) were added to a Schlenk tube containing the supported Au catalyst (1 mol% as Au) under an Ar atmosphere. The progress of the reaction was monitored by thin layer chromatography (TLC) and GC analysis. After the ester or disilane was completely consumed, the solid catalyst was removed by passing the mixture through a 0.45 μm polytetrafluoroethylene (PTFE) filter (Millipore Millex LH). The remaining solution was concentrated by rotary evaporation under reduced pressure without heating. The resulting liquid was purified through silica gel column chromatography (a mixture of hexane and AcOEt) to give the disilyl alkane.


Key Words

alkylsilanes, benzylsilanes, allylsilanes, allenylsilanes, allenes, gold catalysts


ID: J48-Y2023