Mechanism of ketone and alcohol formations from alkenes and alkynes on the head-to-head 2-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex

Reactions of the head-to-head 2-pyridonato-bridged cis-diammineplatinum(III) dinuclear complex having nonequivalent two platinum atoms, Pt(N(2)O(2)) and Pt(N(4)), with p-styrenesulfonate, 2-methyl-2-propene-1-sulfonate, 4-penten-1-ol, and 4-pentyn-1-ol were studied kinetically. Under the pseudo first-order reaction conditions that the concentration of the Pt(III) dinuclear complex is much smaller than that of olefin, a consecutive basically four-step reaction was observed: the olefin pi-coordinates preferentially to the Pt(N(2)O(2)) in the first step (step 1), followed by the second pi-coordination of another olefin molecule to the Pt(N(4)) (step 2). In the next step (step 3), the nucleophilic attack of water to the coordinated olefin triggers the pi-sigma bond conversion on the Pt(N(2)O(2)), and the second pi-bonding olefin molecule on the Pt(N(4)) is released. Finally, reductive elimination occurs to the alkyl group on the Pt(N(2)O(2)) to produce the alkyl compound (step 4). The first water substitution with olefin (step 1) occurs to the diaqua and aquahydroxo forms of the complex, whereas the second substitution (step 2) proceeds either on the coordinated OH(-) on the Pt(N(4)) (path a) or on the coordinatively unsaturated five-coordinate intermediate of the Pt(N(4)) (path b), in addition to the common substitution of H(2)O (path c). The reactions of p-styrenesulfonate and 2-methyl-2-propene-1-sulfonate proceed through paths b and c, whereas the reactions of 4-penten-1-ol and 4-pentyn-1-ol proceed through paths a and c. This difference reflects the difference of the trans effect and/or trans influence of the pi-coordinated olefins on the Pt(N(2)O(2)). The pentacoordinate state in path b is employed only by the sulfo-olefins, because these exert stronger trans effect. The steps 3 and 4 reflect the effect of the axial alkyl ligand (R) on the charge localization (R-Pt(IV)(N(2)O(2))-Pt(II)(N(4))) and delocalization (R-Pt(III)(N(2)O(2))-Pt(III)(N(4))-OH(2)); when R is p-styrenesulfonate having an electron withdrawing group, the charge localization in the dimer is less pronounced and the water molecule on the Pt(N(4)) atom is retained (R-Pt(III)(N(2)O(2))-Pt(III)(N(4))-OH(2)) in the intermediate state. In both routes, the alkyl group undergoes nucleophilic attack of water, and the oxidized products are released via reductive elimination.     

Rate constants for the reactions of OH radicals with CH3OCF2CF3, CH3OCF2CF2CF3, and CH3OCF(CF3)2

The rate constants for the reactions of OH radicals with CH₃OCF₂CF₃, CH₃OCF₂CF₂CF₃, and CH₃OCF(CF₃)₂ have been measured over the temperature range 250–430 K. Kinetic measurements have been carried out using the flash photolysis, laser photolysis, and discharge flow methods combined respectively with the laser induced fluorescence technique. The influence of impurities in the samples was investigated by using gas‐chromatography. The following Arrhenius expressions were determined: k(CH₃OCF₂CF₃) = (1.90) × 10⁻¹² exp[−(1510 ± 120)/T], k(CH₃OCF₂CF₂CF₃) = (2.06) × 10⁻¹² exp[−(1540 ± 80)/T], and k(CH₃OCF(CF₃)₂) = (1.94) × 10⁻¹² exp[−(1450 ± 70)/T] cm³ molecule⁻¹ s⁻¹. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 846–853, 1999     

Contracted polarization functions for the atoms Ca, Ga–Kr, Sr, and In–Xe

 Contracted Gaussian-type function sets are proposed for polarization functions of the atoms Ga–Kr and In–Xe. We also report polarization functions for Ca and Sr. A segmented contraction scheme is used for its compactness and computational efficiency. The contraction coefficients and orbital exponents are fully optimized to minimize the deviation from accurate atomic natural orbitals. The present polarization functions yield more than 99% of atomic correlation energies predicted by accurate natural orbitals of the same size. Received: 23 February 2001 / Accepted: 19 April 2001 / Published online: 13 June 2001     

New technique for generating high concentrations of gaseous OH radicals in relative rate measurements

We have developed a technique for generating high concentrations of gaseous OH radicals in a reaction chamber. The technique, which involves the UV photolysis of O₃ in the presence of water vapor, was used in combination with the relative rate method to obtain rate constants for reactions of OH radicals with selected species. A key improvement of the technique is that an O₃/O₂ (3%) gas mixture is continuously introduced into the reaction chamber, during the UV irradiation period. An important feature is that a high concentration of OH radicals [(0.53–1.2) × 10¹¹ radicals cm^?3] can be produced during the irradiation in continuous, steady‐state experiment. Using the new technique in conjunction with the relative rate method, we obtained the rate constant for the reaction of CHF₃ (HFC‐23) with OH radicals, k₁. We obtained k₁(298 K) = (3.32 ± 0.20) × 10^?16 and determined the temperature dependence of k₁ to be (0.48 ± 0.13) × 10^?12 exp[?(2180 ± 100)/T] cm³ molecule^?1 s^?1 at 253–328 K using CHF₂CF₃ (HFC‐125) and CHF₂Cl (HCFC‐22) as reference compounds in CHF₃–reference–H₂O gas mixtures. The value of k₁ obtained in this study is in agreement with previous measurements of k₁. This result confirms that our technique for generating OH radicals is suitable for obtaining OH radical reaction rate constants of ～10^?16 cm³ molecule^?1 s^?1, provided the rate constants do not depend on pressure. In addition, it also needed to examine whether the reactions of sample and reference compound with O₃ interfere the measurement when selecting this technique. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 317–325, 2003     

Toward the responsible innovation with nanotechnology in Japan: our scope

The societal impacts of nanotechnology have attracted growing attention in the United States and Europe in recent years. In Japan, the National Institute of Advanced Industrial Science and Technology (Technology Information Department) has played a central role in promoting discussions on this topic by collecting information from Japan and overseas, creating a network of the interested parties, and providing a forum for discussion. This paper presents a summary of recent activities in Japan relating to the societal impacts of nanotechnology, fro the launch of the “Nanotechnology and Society” open forum (August 2004) until the “Nanotechnology Debate” discussion forum (February 2007), and outlines the policy recommendations that came out of a project entitled “Research on Facilitation of Public Acceptance of Nanotechnology” (March 2006).     

A new trimethylsilyl triflate-catalyzed 1,3-dipolar cycloaddition leading to pyrrolidines

Pyrrolidines were obtained by a new, trimethylsilyl triflate-catalyzed cycloaddition of an intermediary N-trimethylsilylated methyleneiminium ylide, a 1,3-dipole, to olefinic and acetylenic dipolarophiles.     

Microwave spectroscopic and ab initio studies of pyrolysis products of 2-nitrosopropene (syn form) and its pyrolysis mechanism

The pyrolysis products of CH₂=C(CH₃)---NO (syn form) have been determined by microwave spectroscopy. The pyrolysis products of CH₂=C(CH₃)---NO (syn form) and its ¹⁵N isotopic species were found to be CH₂=O, CH₃CN, and CH₃C¹⁵N. The produce of formaldehyde and methyl cyanide suggests that the C=C and N=O double bonds of CH₂=C(CH₃)---N=O (syn form) were broken. To explain the generation of the two molecules, a four-membered ring molecule (9) as an intermediate, is proposed. The four-membered ring molecule as an intermediate is also supported by ab initio MO calculation. Applying the pyrolysis mechanism obtained for 2-nitrosopropene (syn form) to that of 1,1,2-trichloronitrosoethane, one of its complicated pyrolysis mechanisms was explained. The rotational constants and geometrical parameters of two intermediates, 9 and CH₂=CCl---NO (13), were obtained by ab initio MO calculation (MP2/6-31G**) to predict their microwave spectra.     

A Regulable Internal Cavity inside a Resorcinarene-Based Hemicarcerand

Covalent organic capsules, such as carcerands and hemicarcerands, are an interesting class of molecular hosts. These container molecules have confined spaces capable of hosting small molecules, although the fact that the size of the inner cavities cannot be changed substantially limits the scope of their applications. The title covalently linked container was produced by metal-directed dimerization of a resorcinarene-based cavitand having four 2,2′-bipyridyl arms on the wide rim followed by olefin metathesis at the vertices of the resulting capsule with a second-generation Grubbs catalyst. The covalently linked bipyridyl arms permit expansion of the inner cavity by demetalation. This structural change influences the molecular recognition properties; the metal-coordinated capsule recognizes only 4,4′-diacetoxybiphenyl, whereas the metal-free counterpart can encapsulate not only 4,4′-diacetoxybiphenyl, but also 2,5-disubstituted-1,4-bis(4-acetoxyphenylethynyl)benzene, which is 9.4 Å longer than the former guest. Molecular mechanics calculations predict that the capsule expands the internal cavity to encapsulate the long guest by unfolding the folded conformation of the alkyl chains, which demonstrates the flexible and regulable nature of the cavity. Guest competition experiments show that the preferred guest can be switched by metalation and demetalation. This external-stimuli-responsive guest exchange can be utilized for the development of functional supramolecular systems controlling the uptake, transport, and release of chemicals.