Norihisa Fukaya

Stable aromatic compounds containing heavier Group 14 elements

Abstract This account is devoted to the problem of aromaticity in the chemistry of heavier Group 14 elements: namely cyclic compounds including Si and Ge atoms in the ring. Three-membered, five-membered and six-membered ring systems, possessing aromatic character are described.

Cyclotrigermenium Ion, a Free Germyl Cation with 2π-Electron System

The reaction of tetrakis(tri-t-butylsilyl)cyclotrigermene with trityl tetraphenylborate in benzene produced tris(tri-t-butylsilyl)cyclotrigermenium tetraphenylborate [(t-Bu3SiGe)3 +BPh4 -], which can be isolated as yellow solids stable in the absence of air. The crystal structure of the cyclotrigermenium ion reveals a free germyl cation with 2π-electron system.

Synthesis of Cyclic Sulfites from Epoxides and Sulfur Dioxide with Silica‐Immobilized Homogeneous Catalysts

Quaternary ammonium- and amino-functionalized silica catalysts have been prepared for the selective synthesis of cyclic sulfites from epoxides and sulfur dioxide, demonstrating the effects of immobilizing the homogeneous catalysts on silica. The cycloaddition of sulfur dioxide to various epoxides was conducted under solvent-free conditions at 100 °C. The quaternary ammonium- and amino-functionalized silica catalysts produced cyclic sulfites in high yields (79-96 %) that are comparable to those produced by the homogeneous catalysts. The functionalized silica catalysts could be separated from the product solution by filtration, thereby avoiding the catalytic decomposition of the cyclic sulfite products upon distillation of the product solution. Heterogenization of a homogeneous catalyst by immobilization can, therefore, improve the efficiency of the purification of crude reaction products. Despite a decrease in catalytic activity after each recycling step, the heterogeneous pyridine-functionalized silica catalyst provided high yields after as many as five recycling processes.

A Simple Zinc Catalyst for Carbamate Synthesis Directly from CO2

Several zinc salts were employed as catalysts for the synthesis of carbamates directly from aromatic amines, CO2 , and silicate esters. Zn(OAc)2 offered the best performance among the salts tested. The addition of an N-donor ligand such as 1,10-phenanthroline increased the yield. The best catalytic performance of Zn(OAc)2 can be explained by carboxylate-assisted proton activation. The interaction between the substrate and the catalyst can be observed by chemical shifts in 1 H and 15 Nu2005NMR spectra. Isocyanate was a key intermediate, which was generated from amine and CO2 . Silicate ester was finally converted to siloxane, which was determined by 29 Siu2005NMR. The commercially available catalyst system could be reused. The yield of isolated carbamate could reach up to 96u2009% with various substrates, and the catalytic reaction was amine-selective in the presence of other functional groups.

Cyclotrigermenium Ion by Oxidation of Cyclotrigermene with Trityl Tetrakis {3,5-Bis(Trifluoromethyl)Phenyl}Borate and Trityl Tetrakis(Pentafluoro-Phenyl)Borate. A Stable Free Germyl Cation in the Condensed Phase.

The reaction of tetrakis(tri-t-butylsilyl) cyclotrigermene with Ph3C+z [3,5-(CF3)2C6H3]4B− (TFPB) and Ph3C+z(C6F5)4B− (TPFPB) in benzene produced the stable free tris (tri-t-butylsilyl)cyclotrigermenium ion (2a) with the corresponding tetraarylborate as a counter anion. The crystal structure of 2azTFPB reveals a free germyl cation with 2π-electron system. The three-membered germanium atoms constitute almost an equilateral triangle, similar to that of 2azTPB (TPB = Ph4B−). In contrast to 2azTPB, both 2azTFPB and 2azTPFPB are thermally stable in solution.

Direct synthesis of carbamate from CO2 using a task-specific ionic liquid catalyst

A superbase-derived protic ionic liquid (IL, [DBUH][OAc]) catalyst was used to directly synthesize carbamate from an amine, CO2, and a silicate ester. This IL catalyst was easily prepared using its precursors, DBU, and acetic acid. Using 10 mol% of the catalyst under a CO2 pressure of 5 MPa in acetonitrile at 150 °C, carbamate was isolated in up to 96% yield. Specifically, aliphatic and aromatic amines were activated even though aromatic amines exhibited low activities because of their low pKa values. Other functional groups in amines were barely activated, affording exclusive chemoselectivity for amine activation. Isotope labeling experiments indicated that the proton in the counter cation is crucial in the catalytic cycle to produce water. In addition, a chemical shift corresponding to a mixture of aniline and [DBUH][OAc] was observed in the 1H NMR spectrum, related to the formation of hydrogen bonds between aniline and basic acetate anions. The experimental results indicated that the designed IL catalysts require a protonated cation and a basic anion.

Direct synthesis of tetraalkoxysilanes from silica and alcohols

A new simple and efficient process for synthesizing tetraalkoxysilanes (TROS) directly from silica and alcohols was developed using molecular sieves as dehydrating agents. Using this method, a variety of TROS (R = ethoxy, n-propoxy, or n-butoxy) were obtained over 70% yields within 6 h. We also employed various natural silica sources in this process for practical applications.

Halogen-Free Synthesis of Carbamates from CO2 and Amines Using Titanium Alkoxides

A direct synthesis of carbamates from amines and carbon dioxide in the presence of Ti(OR)4 (R=nBu (1), Me (2), Et (3), nPr (4)) was investigated. Aniline was reacted with titanium n-butoxide (1) in the presence of carbon dioxide (5u2005MPa) to give the corresponding n-butyl N-phenylcarbamate (BPC) in nearly quantitative yield (99u2009%) within 20u2005min. Furthermore, 1 could be regenerated upon reaction with n-butanol during water removal. The recovered 1 could then be reused in a subsequent reaction.

Synthesis and Structure of Cyclotrigermenium Salts of Tetrakis{3,5-bis(trifluoromethyl)phenyl}borate, Tetrakis(pentafluorophenyl)borate and Tetrakis{4-[tert-butyl(dimethyl)silyl]-2,3,5,6-tetrafluorophenyl}borate: A Stable Free Germyl Cation in the Condensed Phase

The reaction of tetrakis(tri-tert-butylsilyl)cyclotrigermene (1a) with Ph3C+[3,5-(CF3)2C6H3]4B− (TFPB−), Ph3C+(C6F5)4B− (TPFPB−), and Ph3C+[4-(tBuMe2Si)C6F4]4B− (TSFPB−) in benzene produced the stable free tris(tri-tert-butylsilyl)cyclotrigermenium ion (2a+) with the corresponding tetraarylborate as the counterion. The crystal structures of 2a+TFPB− and 2a+TSFPB− reveal a free germyl cation with a two π-electron system. The three-membered ring of germanium atoms constitutes an almost equilateral triangle. The cyclotrigermenium tetraarylborates, 2a+TFPB−, 2a+TPFPB−, and 2a+TSFPB−, are stable in solution. The spectroscopic data show that 2a+ is a free germyl cation, does not coordinate to either the solvent molecules (dichloromethane, chloroform, toluene, or diethyl ether) or the counter anions (TFPB−, TPFPB−, or TSFPB−). The tris(tri-tert-butylgermyl)cyclotrigermenium ion (2b+) was also characterized.

Feasibility Study of New Synthesis Route of Tetraethoxysilane from Rice Hull Ash

Abstract Recently, a new synthesis route of tetraethoxysilane (TEOS) has been proposed using silica included in rice hull ash (RHA) as the initial raw material. Employing this new route would potentially reduce energy consumption and contribute to mitigate emergent environmental problems. We performed a feasibility assessment of this new synthesis route in a large scale production by comparing with the conventional process in terms of production cost and greenhouse gas emission.