Ruthenium(II)-Bipyridine/NanoC3 N4 Hybrids: Tunable Photochemical Properties by Using Exchangeable Alkali Metal Cations.

A series of nanoporous carbon nitrides that contained a range of alkali metal cations (M@nanoC3 N4 : M=Li+ , Na+ , K+ , Rb+ , and Cs+ ) have been successfully synthesized from as-synthesized g-C3 N4 by delamination with concentrated sulfuric acid, followed by neutralization with aqueous solutions of the corresponding alkali metal hydroxides. Tris(2,2'-bipyridine)ruthenium(II) complexes, [Ru(bpy)3 ]2+ , were grafted onto the carbon nitrides in an effort to explore the physicochemical properties of the deposited [Ru(bpy)3 ]2+ , as well as its photocatalytic activity in the aerobic photooxidation of phenylboronic acid and H2 production from aqueous media in the presence of a Pt co-catalyst under visible-light irradiation. Highly porous nanoC3 N4 could significantly enhance photocatalytic activity, because of its high surface area, owing to its unique porous structure. More interestingly, the photoluminescence intensities of [Ru(bpy)3 ]2+ complexes that were associated with M@nanoC3 N4 increased in the presence of lighter alkali metal cations, which correlated with increased photocatalytic activities for both reactions. This study demonstrates that M@nanoC3 N4 are fascinating supports, in which the local environment of an immobilized metal complex can be precisely controlled by varying the alkali metal cation from Li+ to Cs+ .

Reversible Generation of Labile Secondary Carbocations from Alcohols in the Nanospace of H-Mordenite and Their Long-Lasting Preservation at Ambient Temperature.

Secondary carbocations are rarely observed spectrometrically for prolonged durations at ambient temperatures because of their instability. In this study, when 4,4'-difluorobenzhydrol (1) was mixed with H-mordenite (H-Mor), the 4,4'-difluorodiphenylmethyl cation (2) was generated as the main product, identified by UV-vis and 13C-MAS NMR spectroscopies, and was preserved for over 1 week at ambient temperature. Surprisingly, the polymerization and disproportionation of 1 barely proceeded within the micropores of H-Mor. However, these side reactions prevailed in TfOH and formation of 2 was not observed. Preservation of other secondary carbocations from benzhydrol, 4,4'-dichlorobenzhydrol, and 9-fluorenol was also realized in H-Mor. It was confirmed that the generation of 2 from 1 was controlled by thermodynamic equilibrium rather than kinetic regulations. The equilibrium between 2 and 1 was accompanied by reversible chromism, which could be easily controlled by altering the moisture content in H-Mor. Moreover, novel insights into specific acid catalysis in zeolites densely populated with acid sites on the inner surface of micropores are described herein.

Nickel-supported carbon nitride photocatalyst combined with organic dye for visible-light-driven hydrogen evolution from water.

A noble-metal-free photocatalytic H2 production system consisting of a Ni-based catalyst, visible-light-responsive organic dye, and graphitic carbon nitride (g-C3N4) as a support has been developed. Characterization by means of XAFS revealed that the deposition of a trinuclear Ni precursor complex, Ni(NiL2)2Cl2 (L = ß-mercaptoethylamine), on the g-C3N4 affords a monomeric Ni(ii) species involving ß-mercaptoethylamine and aqua ligands in an octahedral coordination geometry. Such a Ni species acts as a hydrogen production site from an aqueous solution without an electron relay reagent by combining with thiazole orange (TO) as a photosensitizer. The emission of the attached TO at around 550 nm decreases with increasing loading amount of Ni catalyst, suggesting electron transfer from TO to the Ni catalyst via the g-C3N4 support. Leaching and agglomeration of the active Ni catalyst and TO are not observed during the photocatalytic reaction. Moreover, the use of highly porous carbon nitride (nanoporous carbon nitride; nanoC3N4) is proven to significantly enhance the photocatalytic activity because of the high surface area due to the unique porous structure as well as high absorption and emission properties of TO associated with nanoC3N4.

Sulfated mesoporous alumina: a highly effective solid strong base catalyst for the Tishchenko reaction in supercritical carbon dioxide.

Heterogeneous strong base catalysis for the intramolecular Tishchenko reaction of aromatic 1,2-dicarbaldehydes to the corresponding phthalides in supercritical CO2CscCO2 has been realized with mesoporous alumina containing SO4(2-) ions in the alumina framework (mesoAl2O3/SO4(2-)). Infrared spectroscopy of pyrrole adsorbed on the alumina and strong poisoning by a weak Brönsted acid of methanol revealed that the SO4(2-) ions in the framework slightly suppressed the average strength of base sites (O2-) on mesoAl2O3/SO4(2-), but there exists a small number of strong base sites that promote the Tishchenko reaction in scCO2. Although the intramolecular Tishchenko reaction of phthalaldehyde to phthalide in scCO2 was somewhat slower than those in organic solvents such as tetrahydrofuran (THF) and benzene, the addition of a small amount of THF as a cosolvent remarkably increased the reaction rate; the reaction in the scCO2-THF system proceeded 1.5-fold faster than those in pure benzene and THF solvents.

Formaldehyde encapsulated in zeolite: a long-lived, highly activated one-carbon electrophile to carbonyl-ene reactions.

Gaseous formaldehyde is extremely unstable and readily undergoes self-polymerization to a solid paraformaldehyde or disproportionation to methanol and formic acid in the presence of moisture. We disclose a simple method to stably store such a labile formaldehyde as a monomer in a nanoporous faujasite zeolite at 5 degrees C for at least 50 days without self-polymerization or disproportionation. The greater stability of formaldehyde encapsulated in zeolite was confirmed by 13C MAS NMR spectroscopy. Formaldehyde was not only stabilized within the zeolite cages but functioned as a powerful electrophile toward various olefins. Zeolite-encapsulated formaldehyde was proved to be a stable but highly reactive C1 reagent.

Catalytic enantioselective epoxidation of homoallylic alcohols by chiral zirconium complexes.

Catalytic enantioselective epoxidation of homoallylic alcohols using Zr(Ot-Bu)(4) and tartrate ester (or tartramide) has been developed. In the Zr(Ot-Bu)(4)/diisopropyl tartrate-catalyzed epoxidation, the reverse of the enantiofacial preference was observed, depending on the Zr/ligand ratios of 1:1 or 1:2. [reaction--see text]

Practical carbonyl-ene reactions of alpha-methylstyrenes with paraformaldehyde promoted by a combined system of boron trifluoride and molecular sieves 4A.

[reaction: see text] A combined system of boron trifluoride and molecular sieves is an efficient promoter for the carbonyl-ene reaction of alpha-methylsyrenes with paraformaldehyde. The coexistence of BF3 x OEt2 and molecular sieves 4A is essential for obtaining high yields of ene products.