Hirohisa Tsuzuki

NMR spectroscopic and X-ray crystallographic studies of calix[4]arene·Ag+complexes. Influence of bound Ag+ on C2v–C2v interconversion in cone-calix[4]arenes

The Ag+ complexes of conformationally immobilized tetra-O-propylcalix[4]arene with a cone or a partial-cone conformation (cone-2Prn or partial-cone-2Prn, respectively) have been successfully analysed by X-ray crystallography. In both complexes Ag+ was bound to the upper rim cavity, sandwiched by the two para carbons in the distal phenyl units. The findings provide clear evidence for π-base participation. In particular, the basic calix[4]arene skeleton in partial-cone-2Prn·Ag+ is almost the same as that in partial-cone-2Prnitself. This establishes that partial-cone-2R possesses two distal benzene rings ideally preorganized for Ag+-binding. 1H NMR spectroscopic studies for the Ag+ complexes in solution indicated that Ag+ is bound to the same site as that in the solid state. In conformationally mobile 2Me, which exists in solution in equilibrium between cone and partial-cone, Ag+ induced a shift of the equilibrium to partial-cone to form the partial-cone-2Me·Ag+complex. This is ascribed to the ideal preorganization in partial-cone-2R for the Ag+-binding. These results are of great significance for an understanding of π-base participation in the metal-binding events and have important implications on the cation–π interaction in biological systems.

Organic reaction in water. Part 5.1 Novel synthesis of anilines by zinc metal-mediated chemoselective reduction of nitroarenes

Nitroarenes can be reduced in high yields to the corresponding anilines using zinc metal and NH4Cl in water without any organic solvent at 80 °C with a simple procedure at low cost. The procedure is powerful enough to reduce sterically hindered 2,6-dimethylnitrobenzene and is chemoselective for nitro groups; ester, amide and halide substituents on aromatic rings are unaffected.

OBSERVATION OF SI CLUSTER FORMATION IN SIO2 FILMS THROUGH ANNEALING PROCESS USING X-RAY PHOTOELECTRON SPECTROSCOPY AND INFRARED TECHNIQUES

SiO2 films having high breakdown characteristics were deposited by a sputtering-type electron cyclotron resonance microwave plasma at room temperature. As-deposited films were annealed in an Ar ambient at temperatures ranging from 450 to 1000 °C. Transmitted infrared (IR) absorption and x-ray photoelectron spectroscopy (XPS) were used to characterize the as-deposited and annealed films. XPS measurements indicated that the as-deposited films had an approximately stoichiometric composition containing a few intermediate SiOx(x≠2) species and Ar atoms around some dangling-bond defects. The dependence of XPS spectra on annealing temperature showed that steep diffusion of the Ar atoms occurs at annealing temperatures of 450–550 °C and the SiOx species separate into SiO2 phase and Si clusters by an annealing process of 750–950 °C. Based on the full width at half-maximum variations of Si 2p XPS spectra and Si–O stretching mode of IR spectra for the annealed films, we discuss the Si cluster formation in SiO2 films...

X-ray crystallographic studies of a 1,3-alternate-calix[4]arene·Na+ complex. Is the cation-π interaction operative between the benzene rings and Na+?

Abstract The structure of a 1,3-alternate-calix[4]arene·Na+ complex was determined by X-ray crystallography for the first time. It showed that two well-preorganized oxygen bases (OCH2CO groups) contribute to the Na+-binding whereas two π-basic benzene rings, unlike those for the K+ complex, are not involved. The complex adopts a highly symmetrical structure, which is the origin of the facile “Na+-tunneling” across the 1,3-alternate-calix[4]arene cavity.

Organic reaction in water. Part 3: A facile method for reduction of aromatic rings using a raney Ni–Al alloy in dilute aqueous alkaline solution under mild conditions

Abstract Reduction of aromatic rings such as phenol, naphthalenes, biphenyls, acenaphthene, and acenaphthylene was smoothly performed using a Raney Ni–Al alloy in dilute aqueous alkaline solution without any organic solvents at 90°C under atmospheric pressure, and the corresponding reduced compounds were obtained in high yields.

HYDROLYSIS OF CONDENSED PHOSPHATES IN AN ANION-EXCHANGE RESIN

The alkaline hydrolysis of diphosphate, triphosphate and cyclo-triphosphate sorbed into anion-exchange resins has been investigated using 31P NMR spectroscopy. Well resolved 31P NMR spectra of the sample species and their hydrolysis products within the resin phase were observed. For diphosphate and triphosphate systems, the rate constant and activation parameters for each hydrolysis reaction are quite similar, both in the resin phase and in a basic solution. For the cyclo-triphosphate system, however, the hydrolysis is significantly retarded compared to that in a solution of tetramethylammonium hydroxide. This retardation is shown to be entirely due to a much more unfavourable ΔH‡ for the reaction in the resin phase. The relationship between mechanisms and reactivities of the hydrolysis in the resin phase is discussed.

Selective functionalization of calix[4]arenes via tricarbonylchromium complexes

Abstract Tricarbonylchromium complexes of 25,26,27,28-tetrapropoxycalix[4]arene conformers (14Pr) were synthesized. Since the benzene ring is activated through complexation with Cr(CO)3, the functional groups (e.g. [sbnd]D, [sbnd]CH3, and [sbnd]CHO) could be selectively introduced into the Cr(CO)3-complexed benzene ring. The substitution reaction occurred mainly at the p-position. The para selectivity was attributed to the steric crowding being relatively lower than that around the meta and benzyl position. This view was supported by the X-ray crystallographic study of 1,3-alternate-14Pr·(CO)3. This is a novel and general methodology for selective introduction of functional groups into calix[n]arenes.

X-ray crystallographic studies of a Mn(II)-bridged biscalix[4]arene with a large inner cavity

Abstract A complex isolated from a mixture of tetrasodium 5,11,17,23-tetra-sulfonatocalix[4]arene-25,26,27,28-tetrol and Mn(II) has been analyzed by X-ray crystallography. The crystal packing diagram featured a clay-like bilayer structure as reported previously for the analogous crystals. Interestingly, Mn(II) ions present in the hydrophilic layer cross-link two hydrophobic layers through coordination to the sulfonato groups. Because of this complex formation the repeat unit of the layer (12.1 A) is shorter than those for analogous systems (13.7 –15.0 A). The structure features a Mn(II)-bridged biscalix[4]arene with a large inner cavity. X-Ray crystallographic and ESR spectral data show that Mn(II) ions adopt a distorted octahedral coordination geometry with two sulfonato groups occupying the cis coordination. This is a novel coordination mode for a metal-bridged biscalix[4]arene in the solid state.

Medium-sized cyclophanes.

The selective introduction of one or two acetyl groups by direct replacement of tert-butyl groups via the ipso aromatic acetylation of meta-bridged aromatic compounds having two arene rings is described. Acetylation of syn- and anti-di-tert-butyl[n.2]metacyclophanes 3 (n=2,3,4) with acetyl chloride in the presence of TiCl4 gave the ipso-acetylation product at the tert-butyl group. However, only one tert-butyl group is ipso-acetylated under mild reaction conditions in the presence of TiCl4 because of deactivation of the second aromatic ring by the introduced acetyl group. Higher yields of monoacetylated product are obtained from the anti-conformer than the syn-conformer. Therefore, the intra-annular interaction might be much more favorable to stabilize the initial σ-complex intermediate than face-to-face overlap in the case of ipso-acetylation. On the other hand, acetylation of 3 with acetyl chloride in the presence of AlCl3–MeNO2 afforded the two-fold ipso-acetylation product 6 in quantitative yield. Thus, the extent of ipso-acetylation at the tert-butyl groups of 3 was strongly affected by the activity of the acylation catalyst. The presently developed procedure was further applied to the direct removal of a tert-butyl group by electrophilic substitution of tert-butyl-8-methoxy[2.2]MCPs 11, which are prone to give transannular reaction products under electrophilic reaction conditions.

Effects of oxygen content on properties of silicon oxide films prepared at room temperature by sputtering-type electron cyclotron resonance plasma

We present the study of the effects of gas-phase oxygen fraction on properties of silicon oxide films prepared in a sputtering-type electron cyclotron resonance plasma discharge. Dielectric breakdown characteristics of the films are considerably improved by an increase in oxygen flow rate, FO2, with a constant Ar gas flow rate of 16 sccm. Films prepared at FO2 of more than 6 sccm have good dielectric breakdown fields of 9–11 MV/cm, which are comparable with those of high quality thermally grown SiO2. Moreover, the increase of FO2 improved structural properties of the films. Detailed measurements of their composition and microstructure were carried out using ellipsometry, chemical etch rate measurement in a mixture of HF, H2O, and HNO3 (P etch), x-ray photoelectron spectroscopy (XPS), and infrared (IR) spectroscopy techniques. Ellipsometry and XPS measurements indicated that films prepared at FO2 of more than 3 sccm are stoichiometric. Dependence of the IR spectra and P etch rate on FO2 of more than 3 sccm...