Tris(tert-butoxy)siloxy derivatives of boron,including the boronous acid HOB[OSi(O(t)Bu)(3)](2) and the metal (siloxy)boryloxide complex Cp(2)Zr(Me)OB[OSi(O(t)Bu)(3)](2): a remarkable crystal structure with 18 independent molecules in its asymmetric unit

Silanolysis of B(O(t)Bu)(3) with 2 and 3 equiv of HOSi(O(t)Bu)(3) led to the formation of (t)BuOB[OSi(O(t)Bu)(3)](2) (1) and B[OSi(O(t)Bu)(3)](3) (2), respectively. Compounds 1 and 2 are efficient single-source molecular precursors to B/Si/O materials via thermolytic routes in nonpolar media, as demonstrated by the generation of BO(1.5).2SiO(2) (BOSi2(xg)) and BO(1.5).3SiO(2) (BOSi3(xg)) xerogels, respectively. Use of a block copolymer template provided B/Si/O materials (BOSi2(epe) and BOSi3(epe)) with a broad distribution of mesopores (by N(2) porosimetry) and smaller, more uniform particle sizes (by TEM) as compared to the nontemplated materials. Hydrolyses of 1 and 2 with excess H(2)O resulted in formation of the expected amounts of (t)BuOH and HOSi(O(t)Bu)(3); however, reaction of 1 with 1 equiv of H(2)O led to isolation of the new boronous acid HOB[OSi(O(t)Bu)(3)](2) (3). This ligand precursor is well suited for the synthesis of new metal (siloxy)boryloxide complexes via proton-transfer reactions involving the BOH group. The reaction of 3 with Cp(2)ZrMe(2) resulted in formation of Cp(2)Zr(Me)OB[OSi(O(t)Bu)(3)](2) (4) in high yield. This rare example of a transition metal boryloxide complex crystallizes in the triclinic space group Ponemacr; and exhibits a crystal structure with an unprecedented number of independent molecules in its asymmetric unit (i.e., Z' = 18 and Z = 36). This unusual crystal structure presented an opportunity to perform statistical analyses of the metric parameters for the 18 crystallographically independent molecules. Complex 4 readily converts to Cp(2)Zr[OSi(O(t)Bu)(3)](2) (5) upon thermolysis or upon dissolution in Et(2)O at room temperature.     

Homogeneous catalysis with methane. A strategy for the hydromethylation of olefins based on the nondegenerate exchange of alkyl groups and sigma-bond metathesis at scandium

The scandium alkyl Cp*(2)ScCH(2)CMe(3) (2) was synthesized by the addition of a pentane solution of LiCH(2)CMe(3) to Cp*(2)ScCl at low temperature. Compound 2 reacts with the C-H bonds of hydrocarbons including methane, benzene, and cyclopropane to yield the corresponding hydrocarbyl complex and CMe(4). Kinetic studies revealed that the metalation of methane proceeds exclusively via a second-order pathway described by the rate law: rate = k[2][CH(4)] (k = 4.1(3) x 10(-4) M(-1)s(-1) at 26 degrees C). The primary inter- and intramolecular kinetic isotope effects (k(H)/k(D) = 10.2 (CH(4) vs CD(4)) and k(H)/k(D) = 5.2(1) (CH(2)D(2)), respectively) are consistent with a linear transfer of hydrogen from methane to the neopentyl ligand in the transition state. Activation parameters indicate that the transformation involves a highly ordered transition state (DeltaS++ = -36(1) eu) and a modest enthalpic barrier (DeltaH++ = 11.4(1) kcal/mol). High selectivity toward methane activation suggested the participation of this chemistry in a catalytic hydromethylation, which was observed in the slow, Cp*(2)ScMe-catalyzed addition of methane across the double bond of propene to form isobutane.     

The elastic strain energy of crystallographic shear planes in ReO3-related oxides. II. CS plane arrays

The elastic strain energy of the matrix lying between pairs of crystallographic shear (CS) planes in the ReO₃ type structure has been calculated as a function of CS plane spacing and CS plane type. The CS planes considered are {104}, {105}, {106}, {107}, and {001}, and in addition the results for {102} and {103}, reported previously are included. These results are used to discuss and explain the relative stabilities of differing {10m} CS plane arrays and also the relative stabilities of members of the homologous series generated by ordered arrays of these CS planes. The microstructures of arrays of CS planes that may occur in reduced binary or ternary tungsten oxides, which are slightly distorted variants of the ReO₃ type, and in NbO₂F which has the ReO₃ structure are also considered.     

Reversible intramolecular hydride transfer between tantalum and an aromatic ring: an eta(5)-cyclohexadienyl complex as a masked hydride

The methyl triflate complex (2,6-Mes2C6H3N=)(2,6-Mes2C6H3NH)TaMe(OSO2CF3) reacts cleanly with H2 to give the eta5-cyclohexadienyl complex 3. Complex 3 therefore results from the insertion of an arene ring into an M-H bond, which has been proposed as the first step in catalytic arene hydrogenations. This insertion is reversible, such that 3 behaves as a "masked hydride" in its reaction chemistry.     

Generation of a Silylene Complex by the 1,2-Migration of Hydrogen from Silicon to Platinum

An extraordinary downfield - shifted ²⁹ Si{ ¹ H} NMR signal is seen at δ=338.5 for the platinum silylene complex [(dippe)(H)Pt=SiMes₂][MeB(C₆F₅)₃] ( 2 ). This remarkably stable metal silylene complex was obtained from 1 in the first intramolecular 1,2-hydride migration from silicon to a transition metal. dippe=iPr₂PCH₂CH₂PiPr₂, Mes=2,4,6-Me₃C₆H₂.     

Positron surface states bound by the Newns-Barton potential

The binding energies and eigenfunctions of the surface states of positrons outside materials with negative positron affinity are considered. When the material is represented by a continuum hydrodynamic model with finite dispersion the potential takes the Newns-Barton form. The characteristic material parameter is B = ω_p/β where ω_p is the bulk plasma frequency and $\text{β ? √}\text{3}\text{5}\text{x}$ the Fermi velocity. For aluminium B ? 0.6a^?1 (a is the Bohr radius) and the Newns-Barton potential yields a ground state binding energy E⁽¹⁾ ? 0.46 ev - considerably smaller than the binding energy of the pure image (or non dispersive) potential for which E⁽¹⁾ ? 0.85 ev.     

Liquid-phase oxidation of alkylaromatics by a H-atom transfer mechanism with a new heterogeneous CoSBA-15 catalyst

A new pseudo-tetrahedral Co(II) complex has been grafted onto the surface of SBA-15 and successfully utilized for the catalytic oxidization of alkylaromatic substrates with tert-butyl hydroperoxide (TBHP)via an H-atom transfer mechanism.     

Mode mixing and dielectric function

We consider a model in which a bilinear Hamiltonian couples an optically inactive mode (magnon) with optically active modes (phonons). The dielectric function is derived both by a classical method and by the use of linear response theory. It is shown that the low frequency dielectric constant is increased above the value which it has in the absence of interaction.