Rhodium-catalyzed disulfide exchange reaction

A system of RhH(PPh3)4, trifluoromethanesulfonic acid, and (p-tol)3P catalyzes the disulfide exchange reaction. Treatment of two symmetrical dialkyl disulfides with the catalyst provides an equilibrium mixture of three disulfides within 15 min in refluxing acetone. The catalyst is active after reaching the equilibrium, and addition of a disulfide to the mixture changes the ratio of the products. The use of 4 mol equiv excess of one of the disulfides provides the unsymmetrical disulfide in a yield exceeding 80%. Disulfide-containing peptides also undergo an exchange reaction. The reactions of diaryl disulfides and dialkyl disulfides are even faster, and reach equilibrium within 5 min at room temperature in the presence of the rhodium complex and 1,2-bis(diphenylphosphino)ethane (dppe). This exchange reaction is considerably affected by the substituents on the disulfides. Treatment of diphenyl disulfide, di(p-tolyl) disulfide, and bis(sec-butyl) disulfide yields phenyl p-tolyl disulfide at room temperature with unchanged bis(sec-butyl) disulfide; random disproportionation occurs at reflux. The rhodium catalysis can be used for the exchange reaction of disulfides and diselenides giving selenosulfides as well as disulfides and ditellurides giving tellurinosulfides.     

Theoretical study on second hyperpolarizabilities of phenylacetylene dendrimer: toward an understanding of structure-property relation in NLO responses of fractal antenna dendrimers

This contribution explores the relation between molecular second hyperpolarizabilities (gamma) and molecular architecture in phenylacetylene dendrimers using the semiempirical molecular orbital method, that is, INDO/S method. The orientationally averaged gamma of a large-size phenylacetylene dendrimer, which is composed of 24 units of phenylacetylenes and is referred to as D25, is found to be about 50 times as large as that of the diphenylacetylene monomer. In contrast, the gamma(s)() value of D25 is found to be about 6 times as small as that of the para-substituted phenylacetylene oligomer (L25) composed of 24 units of phenylacetylenes. To investigate the structure-property relation in gamma for D25 and L25, we examine the spatial contributions of electrons to gamma values using gamma density analysis. The present analysis reveals that the dominant contributions of electrons to gamma of D25 are localized in the linear-leg regions parallel to the applied electric field and the contributions are also well segmented at the meta-connected points (benzene rings), while the spatial distribution of the gamma density of L25 is extended over the whole region of the chain, and the dominant contribution stems from the both-end regions. It is found for D25 that the magnitude of contributions to gamma in the internal region is more enhanced than that in the outer region. We further found that the magnitudes of contributions in internal linear-leg regions of D25 are somewhat larger than those of the same-size isolated linear-leg molecules. This suggests that the slightly remaining pi-conjugations via the meta-branching points still enhance the contributions to gamma localized in the linear-leg regions. These features of spatial contributions to gamma of D25 are found to originate in the fractal architecture, in which pi-conjugation lengths in the linear-leg region increase on going from the periphery to the core. Finally, fractal antenna dendrimers are expected to be promising novel nonlinear optical (NLO) substances with a controllability of the magnitude and spatial contribution of the third-order NLO properties.     

Reaction of [M(eta3-allyl)(eta2-amidinato)(CO)2(pyridine)] complexes (M = Mo, W) with bidentate ligands: nitrogen donor vs. phosphorus donor

The reactivity of amidinato complexes of molybdenum and tungsten bearing pyridine as a labile ligand, [M(eta(3)-allyl)(eta(2)-amidinato)(CO)(2)(pyridine)](M = Mo; 1-Mo, M = W; 1-W), toward bidentate ligands such as 1,10-phenanthroline (phen) and 1,2-bis(diphenylphosphino)ethane (dppe) was investigated. The reaction of 1 with phen at ambient temperature resulted in the formation of monodentate amidinato complexes, [M(eta(3)-allyl)(eta(1)-amidinato)(CO)(2)(eta(2)-phen)](M = Mo; 2-Mo, M = W; 2-W), which has pseudo-octahedral geometry with the amidinato ligand coordinated to the metal in an eta(1)-fashion. The phen ligand was located coplanar with two CO ligands and the eta(1)-amidinato ligand was positioned trans to the eta(3)-allyl ligand. In solution, both complexes 2-Mo and 2-W showed fluxionality, and complex 2-Mo afforded allylamidine (3) on heating in solution. In the reaction of 1 with dppe at ambient temperature, the simple substitution reaction took place to give dppe-bridged binuclear complexes [{M(eta(3)-allyl)(eta(2)-amidinato)(CO)(2)}(2)(mu-dppe)](M = Mo; 5-Mo, M = W; 5-W), whereas mononuclear monocarbonyl complexes [M(eta(3)-allyl)(eta(2)-amidinato)(CO)(eta(2)-dppe)](M = Mo; 6-Mo, M = W; 6-W) were obtained under acetonitrile- or toluene-refluxing conditions. Mononuclear complex 6 was also obtained by the reaction of binuclear complex 5 with 0.5 equivalents of dppe under refluxing in acetonitrile or in toluene. The X-ray analyses and variable-temperature (31)P NMR spectroscopy of complex 6 indicated the existence of the rotational isomers of the eta(3)-allyl ligand, i.e., endo and exo forms, with respect to the carbonyl ligand. The different reactivity of complex 1 toward phen and dppe seems to have come from the difference in the pi-acceptability of each bidentate ligand.     

Novel synthesis of N-alkyl-3,4-disubstituted pyrrolidine-2,5-diones: Condensation of α-oxoketene O,N-acetals and maleic anhydride

A novel method for the synthesis of N-alkyl-3-acyl-4-alkoxycarbonylmethylpyrrolidine-2,5-diones (3) was accomplished. α-Oxoketene O,N-acetals (1) reacted with maleic anhydride (2) at 80–110 °C for 5 h without solvent to give 3 in moderate to good yield (36–74%). Single X-ray crystallographic analysis showed that the two substituents on C-3 and C-4 were trans.     

Quantum tunneling of magnetization in a new [Mn18]2+ single-molecule magnet with s = 13

The reaction between 2-(hydroxyethyl)pyridine (hepH) and a 2:1 molar mixture of [Mn3O(O2CMe)6(py)3](ClO4) and [Mn3O(O2CMe)6(py)3](py) in MeCN leads to isolation of [Mn18O14(O2CMe)18(hep)4(hepH)2(H2O)2](ClO4)2 (1) in 10% yield. The complex is 2MnII,16MnIII and consists of a Mn4O6 central unit to either side of which is attached a Mn7O9 unit. Magnetization data collected in the 2.0-4.0 K and 20-50 kG ranges were fit to yield S = 13, g = 1.86, and D = -0.13 cm-1 = -0.19 K, where D is the axial zero-field splitting parameter. AC susceptibility studies in the 0.04-4.0 K range at frequencies up to 996 Hz display out-of-phase (chiM' ') signals, indicative of a single-molecule magnet (SMM). Magnetization vs applied DC field scans exhibit hysteresis at <1.0 K, confirming 1 to be a SMM. DC magnetization decay data were collected on both a microcrystalline sample and a single crystal, and the combined data were used to construct an Arrhenius plot. Between 3.50 and 0.50 K, the relaxation rate is temperature-dependent with an effective barrier to relaxation (Ueff) of 14.8 cm-1 = 21.3 K. Below ca. 0.25 K, the relaxation rate is temperature-independent at 1.3 x 10-8 s-1, indicative of quantum tunneling of magnetization (QTM) between the lowest energy Ms = +/-13 levels of the S = 13 state. Complex 1 is both the largest spin and highest nuclearity SMM to exhibit QTM.     

The transition of three types of three-phase behavior in a temperature-composition space of water/C12EO6/propanol/heptane system

 The change of three-phase behavior of a water/hexaethylene-glycol dodecyl ether (C₁₂EO₆)/propanol/heptane system was studied with increasing temperature (30.0–48.9 °C). A cone-like three-phase body consisting of aqueous (W), surfactant (D_p), and oil (O) phases is formed in the composition tetrahedron at lower temperatures. The body is expanded with increasing temperature, and touches the water–C₁₂EO₆–heptane triangle (the base) at 44.8 °C. At about 45.6 °C the loci of the D_p and O phases meet and cut off at a critical double end point and the three-phase body separates into two bodies: one has a chiral shape and the other is unclosed. The unclosed body is transformed with the change of shape of the tie triangle on the base as temperature increases and leaves from the base at 48.9 °C. A closed-loop miscibility gap between middle surfactant (D^′ _p) and O phases or a cone-like three-phase body is formed inside the composition tetrahedron at higher temperatures. The roles of C₁₂EO₆ and propanol are also discussed. Received: 14 April 1998 Accepted: 15 July 1998     

The effect of solvents on asymmetric induction cationic copolymerization of l-menthyl vinyl ether with indene

Cationic copolymerization of l-menthyl vinyl ether (l-MVE) with indene (IN) was carried out in several solvents with BF₃OEt₂ as catalyst at 0°C. The solvents used in this study were selected toluene (Tol), chloroform (CHCl₃), chlorobenzene (BzCl), 1,2-dichloroethane (EtCl₂), and nitrobenzene; (BzNO₂)/Tol = 65/35 mixture solvent. l-Methyl residue, which is an optically active side chain of copolymer produced by cationic copolymerization, was removed with dry hydrogen bromide gas by ether cleavage reaction. The copolymer [vinyl alcohol(VA)–lN], produced by the ether cleavage reaction, also showed optical rotation. From this result, therefore, it was concluded that asymmetric induction takes place in the copolymer main chain. The efficiency of asymmetric induction was determined by the measurement of optical rotation of VA–IN copolymer after the ether cleavage reaction. The efficiency of asymmetric induction in the copolymer main chain developed from the variation on polymerization solvents; the order was Tol > EtCl₂ > BzCl > CHCl₃ > BzNO₂/Tol (65/35) mixture solvent.     

Redox-responsive supramolecular polymeric networks having double-threaded inclusion complexes

Stimuli-responsive hydrogels have attracted attention as soft actuators that act similarly to muscles. In this work, hydrogel actuators controlled by host–guest interactions have been developed. The introduction of a 1:1 inclusion complex into a hydrogel is a popular design for achieving a change in cross-linking density. To realize faster and larger deformation properties, the introduction of a 1:2 inclusion complex is effective because the alteration in cross-linking density in a hydrogel with 1:2 complexes is larger than that in a hydrogel with 1:1 complexes. A redox-responsive hydrogel actuator cross-linked with 1:2 inclusion complexes is designed, where γ-cyclodextrin (γCD) and viologens modified with an alkyl chain derivative (VC11) were employed as the host and guest units, respectively. γCD includes two VC11 molecules in its cavity. The obtained γCD–VC11 hydrogel cross-linked with the 1:2 complex showed faster and larger deformation behaviour than the αCD–VC11 and the βCD–VC11 hydrogels cross-linked with a 1:1 complex. The deformation ratio and response speed of the γCD–VC11 hydrogel, which forms a supramolecular cross-linking structure by stimuli, are 3 and 11 times larger, respectively, than those of our previous hydrogel consisting of a βCD/ferrocene 1:1 inclusion complex.

A hydrogel actuator with a 1:2 host–guest complex controlled by redox stimuli has been developed to realize faster and larger deformation.     

Total synthesis of (±)-methyl-kinamycin C

The first total synthesis of the proposed structure for methyl-kinamycin C (methyl-KC), derived from KC, was achieved via two key steps: Diels-Alder reaction of benzindenone and Danishefsky-type diene, and the stereoselective construction of highly oxygenated D ring. Good accordance of the spectral data of synthesized title compound with those of natural KC and its derivative was observed.     

Induced circular dichroism spectra of 2-(2,4,6-cycloheptatrien-1-ylidene)-4-cyclopentene-1,3-dione included inβ-cyclodextrin

The assignment of the absorption spectra of 2-(2,4,6-cycloheptatrien-1-ylidene)-4-cyclopentene-1,3-dione (1) is reported by measuring the induced circular dichroism spectra of the β-cyclodextrin complex with1. It is concluded from the signs of the induced circular dichroism bands that the first absorption band (17.1×10³–34.3×10³ cm^?1) is composed of three electronic transitions having perpendicular, parallel and perpendicular polarizations with respect to the long axis (z) of1. The second absorption band (34.3×10³–42.8×10³ cm^?1) is composed of two electronic transitions having parallel polarizations with respect to the long axis of1 and the third absorption band (42.8×10³–47.1×10³ cm^?1) has the transition dipole moment perpendicular to the long axis of1. Our experimental assignments are supported by CNDO/S CI calculations.