Preparation of a copper ion complex of sterically congested diphenyldiazomethanes having a pyridine ligand and characterization of their photoproducts

To show that persistent high-spin polycarbenes can be realized by utilizing hetero spin systems, two diphenyldiazomethanes having pyridyl groups, i.e., bis{4-(4-pyridyl)-2,6-dimethylphenyl}diazomethane (4,4'-DPy-1-N(2)) and {2,4-di(4-pyridyl)-6-bromophenyl}(2,6-dimethyl-4-tert-butylphenyl)diazomethane (2,4-DPy-1-N(2)), were prepared. Triplet carbenes, 4,4'-DPy-1 and 2,4-DPy-1, generated by photolysis of the corresponding diazomethanes were characterized by spectroscopic means (ESR and UV/vis in matrix at low temperatures and laser flash photolysis in solution at room temperature). The results showed that they were fairly persistent. Magnetic properties of the photoproducts from a 1:1 complex between DPy-1-N(2) and Cu(hfac)(2) (hfac = hexafluoroacetylacetonate) were characterized by ESR and a superconducting quantum interference device (SQUID) magneto/susceptometer. The field dependences of magnetization for the complexes, expressed by using M versus H/T plots, were analyzed in terms of the Brillouin function to be S = 6.80 (F = 0.60) for the 1:1 complex of 4,4'-DPy-1 and Cu(hfac)(2) and S = 3.71 (F = 0.73) for the 1:1 complex of 2,4-DPy-1 and Cu(hfac)(2) at 2.0 K. Thus, it has been demonstrated that a high-spin species is actually generated in the photoproducts and that the complexed carbenes showed significant stability.     

Synthesis of microtubes with a surface of "house of cards" structure via needlelike particles and control of their pore size

The conditions for synthesizing microtubes with a surface of "house of cards" structure via needlelike particles were examined in detail. Magnesium carbonate trihydrate was formed as a metastable phase in the reaction process using magnesium hydroxide and carbon dioxide as starting materials. Subsequently, in the formation of basic magnesium carbonate from magnesium carbonate trihydrate, microtubes with a surface of house of cards structure were obtained via needlelike particles of magnesium carbonate trihydrate under certain conditions where the temperature and added amount of sodium hydroxide were properly controlled. The pore size of the microtubes could be controlled within a range of 0.5-6 microm by adjusting the condition of needlelike particle formation. In addition, the sustainability of naphthalene release from the microtube was found to be about 6 times higher than that from naphthalene crystal.     

Alternating copolymerization of propylene oxide and carbon dioxide with an alumina supported diethylzinc catalyst

Diethylzinc was allowed to react with γ-alumina in n-heptane at 50°C, and the copolymerization of propylene oxide and carbon dioxide was investigated in some detail at 30–90°C by using the reaction product as a catalyst. From an analysis of the catalyst it was found that diethylzinc reacted with the surface hydroxyl groups of γ-alumina mainly to give the following A-type species by evolving ethane: The catalyst showed considerably high activity for the copolymerization. The polymer obtained was a white solid with a high molecular weight soluble in benzene, acetone, dioxane, and methylene chloride and insoluble in diethyl ether and water. It was confirmed as an alternate copolymer of propylene oxide and carbon dioxide. The copolymerization was also conducted with a reaction mixture of the catalyst and catechol in which the molar ratio of catechol to the A-type species was varied. The copolymerization activity decreased linearly with an increase in the molar ratio and disappeared completely at the molar ratio of unity. On the basis of these results it has been concluded that the A-type is the true active species for the copolymerization.     

Photochemical transformation of a dithioacetal S-oxide into the corresponding aldehyde

Irradiation of an aldehyde dithioacetal S-oxide gives the corresponding aldehyde. The mechanism of this photochemical transformation is discussed and its application to organic synthesis is also described.     

Generation, reactions, and kinetics of sterically congested triplet diphenylcarbenes. Effects of bromine groups.

A series of polybrominated diphenylcarbenes (DPCs) are generated by irradiation of the corresponding precursor diazomethanes, and their reactivities are investigated by means of low-temperature spectroscopies as well as laser flash photolysis. Triplet bis(2,4,6-tribromophenyl)carbene was shown to decay by undergoing dimerization and to have a half-life of 1 s in a degassed benzene solution at room temperature, some 6 orders of magnitude longer-lived than the parent DPC. Anomalous effects of para substituents on the stability of the triplet are noted. Thus, while the replacement of a 4-bromine group with a methyl group resulted in a sharp decrease in the lifetime, introduction of a tert-butyl group resulted in a dramatic increase in the lifetime; triplet bis(2,6-dibromo-4-tert-butylphenyl)carbene was shown to have a half-life of 16 s in solution at room temperature. Attempts to increase the stability of these polybrominated DPCs by buttressing effects of a m-bromine group and by the synergetic effect of bromine and methyl groups are also described.     

Diels-alder reactions of 2-pyrones with acyclic dienophiles and hydrolyses of the mono-adducts

Diels-Alder reactions of 2-pyrone (1) with fumaronitrile and maleonitrile afforded regio- and stereo-specific mono-adducts 3a and 3b , respectively. The reaction of 1 with acrylonitrile gave a bis-adduct. The reaction of 4,6-dimethyl-2-pyrone (7) with dimethyl fumarate and dimethyl maleate at higher temperature gave benzene derivatives. The low reactivity of 7 and the instability of the mono-adducts with 7 were considered from the existence of back reaction and easy elimination of methyl formate, respectively. Hydrolyses of the mono-adducts of 2-pyrones gave polyfunctionalized cyclohexenes and elimination products generated from the preferencial trans-elimination of the leaving groups.     

Triplet diphenylcarbenes protected by (trimethylsilyl)ethynyl groups

(2,4,6-Tribromophenyl)(4-tert-butyl-2,6-dimethylphenyl)diazomethane (1a) was shown to be stable enough to survive Sonogashira coupling reaction conditions at an elevated temperature and gave not only a para-monosubstituted product, (4-trimethylsilylethynyl-2,6-dibromophenyl)(4-tert-butyl-2,6-dimethylphenyl)diazomethane (1b), but also a disubstituted one, [2,4-bis(trimethylsilylethynyl)-6-bromophenyl](4-tert-butyl-2,6-dimethylphenyl)diazomethane (1c), and a trisubstituted product, [2,4,6-tris(trimethylsilylethynyl)phenyl](4-tert-butyl-2,6-dimethylphenyl)diazomethane (1d). Triplet diphenylcarbenes (DPCs) generated by photolysis of those ethynylated diphenyldiazomethanes were characterized by ESR and UV-vis spectroscopies at low temperature and laser flash photolysis techniques in solution at room temperature. Although ESR data indicated that ethynyl groups at the ortho positions are likely to stabilize triplet DPCs both sterically and electronically more effectively than o-bromine groups, kinetic studies suggested that the stability of triplet DPCs is not increased by o-ethynyl groups, as opposed to o-bromine groups. It is likely that triplet DPCs decay by interacting with the o-ethynyl groups.     

Thia­mine tetra­phenyl­borate monohydrate: a two‐dimensional hydrogen‐bonded network with (4,4)‐topology

The title compound, 3‐[(4‐amino‐2‐methyl­pyrimidin‐5‐yl)­meth­yl]‐5‐(2‐hydroxy­eth­yl)‐4‐methyl­thia­zolium tetra­phenyl­borate monohydrate, C₁₂H₁₇N₄OS⁺·C₂₄H₂₀B⁻·H₂O, is a salt in which the thiamine cations are linked by hydrogen bonds into a two‐dimensional network having (4,4)‐topology. The stacked sheets form channels, which are occupied by the anions; the cations and anions are linked by C—H⋯π(arene) hydrogen bonds.     

Acid/base-regulated reversible electron transfer disproportionation of N–N linked bicarbazole and biacridine derivatives

Regulation of electron transfer on organic substances by external stimuli is a fundamental issue in science and technology, which affects organic materials, chemical synthesis, and biological metabolism. Nevertheless, acid/base-responsive organic materials that exhibit reversible electron transfer have not been well studied and developed, owing to the difficulty in inventing a mechanism to associate acid/base stimuli and electron transfer. We discovered a new phenomenon in which N–N linked bicarbazole (BC) and tetramethylbiacridine (TBA) derivatives undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species. The reaction occurs through a biradical intermediate generated by the acid-triggered N–N bond cleavage reaction of BC or TBA, which acts as a two electron acceptor to undergo electron transfer reactions with two equivalents of BC or TBA. In addition, in the case of TBA the disproportionation reaction is highly reversible through neutralization with NEt₃, which recovers TBA through back electron transfer and N–N bond formation reactions. This highly reversible electron transfer reaction is possible due to the association between the acid stimulus and electron transfer via the acid-regulated N–N bond cleavage/formation reactions which provide an efficient switching mechanism, the ability of the organic molecules to act as multi-electron donors and acceptors, the extraordinary stability of the radical species, the highly selective reactivity, and the balance of the redox potentials. This discovery provides new design concepts for acid/base-regulated organic electron transfer systems, chemical reagents, or organic materials.