Search

The various amide-silyl ligand exchanges and equilibria that exist among the group 4 amide and silyl complexes are explained. The analysis reveals that most of these silyl complexes are prepared by replacing the halide ligands in the M-X complexes by silyl atoms.

Several experiments are conducted to explain the kinetics of the preparation and formation of a group of tungsten alkyl alkylidene complexes with different reactivities. The complexes are formed when the tautomeric mixtures undergo a rate-determining step, an [alpha]-hydrogen abstraction, which is then followed by phosphine coordination to give the product.

The syntheses, structures, and magnetic properties of four polynuclear copper(II) complexes with derivatives of 1,2,4-trizole and pivalate ligands are presented. The successful isolation of 1-4 confirms that the mixed, versatile pivalate and the derivatives of 1,2,4-triazole ligands are effective in forming the nonlinear polynuclear metal complexes.

The synthesis of zirconium, hafnium, and tantalum amide silyl complexes are described. The novel reactions of silyl ligands, gamma-hydrogen abstraction to give metallaheterocyclic moiety were investigated.

The synthesis and characterization of (E)- and (Z)-(2-substituted-1,2-dilfluoroethenyl)stannanes and fluorinated stannanes silanes are described. The method involves the reaction of the corresponding silanes with tributylin chloride in DMF at 80 degrees C, in the presence of potassium flouride. The conditions and mechanisms for the reactions are discussed.

The synthesis of deuterium-labeled Ta[(C[D.sub.2][Bu.sup.t]).sub.5] from the reactions of [([Bu.sup.t]C[D.sub.2]).sub.3]Ta[Cl.sub.2] with 2 equiv of [Bu.sup.t]C[D.sub.2]Li as well as [([Bu.sup.t]C[D.sub.2]).sub.4]TaCl with 1 equiv of [Bu.sup.t]C[D.sub.2]Li is described. The deuterium-labeled Ta[(C[D.sub.2][Bu.sup.t]).sub.5] is found to have much longer life and fewer peaks in the [super 1]H NMR spectra than pentaneopentyltantalum, Ta[(C[H.sub.2][Bu.sup.t]).sub.5] due to a kinetic isotope effect.

The article explains the formation of various aminoxy and unusual (aminomethyl)amide oxo complexes by the reacting Ta[(N[Me.sub.2]).sub.5] with [O.sub.2]. The peroxide ligand is found to play a very important role in the reaction.

Kinetic studies are performed for the substitution of the first silyl ligand in [([Me.sub.3]N).sub.3]Ta[[Si[(Si[Me.sub.3]).sub.3]].sub.2] by Li[(THF).sub.3]SiBu[super i][Ph.sub.2] (THF = tetrahydrofuran). The results have shown that the reaction might follow a dissociative pathway in the presence of excess Li[(THF).sub.3]SiBu[super i][Ph.sub.2] and the polar solvent THF has promoted the substitution.

The recent research in the development and applications of sol-gel sensors for concentrated strong acids and bases and metal ions is described. Sol-gels can be specifically designed to meet a variety of needs in the synthetic processes and through the grafting and entrapping of molecules these substrates can be modified to show specificity for analytes of interest.

Reactions of d(super 0) amides M(NMe2)4 (M = Zr, Hf) with O2 yield unusual trinuclear oxo aminoxide complexes M3(NMe2)6(Mu-NMe2)3(Mu3-O)(Mu3-ONMe2) (M = Zr, Hf)) in high yields. Density functional theory calculations are performed to explore the mechanistic pathways in the reactions of model complexes Zr(NR2)4 (R = H, Me) and [Zr(NR2)4]2 (R = H, Me) with triplet O2.

The effect of THF on the rate constants of the conversion is studied, and the kinetics of the reaction was 3.4(0.6)th order with respect to THF. Crystal and molecular structures of H2N-Zr[N(SiMe3)2]3 (2a) and (4a-b) are determined.

Thermodynamic, kinetic and theoretical studies of the exchange between alkylidyne alkyl and bis(alkylidene) tungsten complexes are reported. This exchange involves phosphine coordination, which stabilizes the bis(alkylidene) tautomer so that it is observable at room temperature.

Three novel highly stable 3-D copper(I)- olefin dimers were yielded by the UV irradiation of 2-, 3-, and 4-pyridylacrylic acid with CuICl at 230 nm in 4 N HCl for 1week and subsequent hydrothermal reactions. Copper(I)-olefin complexes are used extensively in a variety of stress responses and developmental processes.

The syntheses of Zn(Norf)(sub 2).4H2) (1) and Zn(H-Norf)(sub 2).(NO3)(sub 2).2H2) (2) and their X-ray crystal structures and fluorescent properties are reported. The results demonstrate that both 1 and 2 show strong blue fluorescent emission and they may be used as an advanced material or blue-emitting diode solvents.

Two dimeric diterpenoids, taxodikaloids A (1) and B (2), have been identified from the seeds of Taxodium ascendens. The diterpenoid structures were established on the basis of comprehensive spectroscopic analysis, and the absolute configuration of taxodikaloid A (1) was further confirmed by single-crystal X-ray diffraction. Both structures feature an unprecedented oxazoline ring linkage connecting two abietane diterpenoid monomers. A plausible biosynthetic pathway for compounds 1 and 2 is proposed. Both compounds show potential neuroprotective activity against Aβ25-35-induced damage in SH-SY5Y cells. [ABSTRACT FROM AUTHOR]

The reaction of W(CH2SiMe3)3(CSiMe3) (1) with DMPE (DMPE = Me2PCH2CH2PMe2) gives an adduct W(CH2SiMe3)3(CSiMe3)(DMPE-P) (4a), which undergoes a rarely observed reversible transformation to its bis-alkylidene tautomer W(CH2SiMe3)2(CHSiMe3)2(DMPE-P) (4b) through α-H migration. The DMPE ligands in both 4aand 4bcontain a dangling P atom (P). Thermodynamic and kinetic studies of the 4a⇌ 4bexchange show that it is slightly endothermic with ΔH° = 5.1(1.1) kcal/mol and ΔS° = 24(4) eu; ΔH1⧧= 7.5(0.9) kcal/mol, ΔS1⧧= −51(2) eu for the 4a→ 4bforward reaction; ΔH−1⧧= 2.0(0.8) kcal/mol, ΔS−1⧧= −76(1) eu for the 4b→ 4areverse reaction. Activation entropies are the major contributors to the activation barriers of the exchange: ΔG1⧧278K= 21.7(1.5) kcal/mol and ΔG−1⧧278K= 23.1(1.1) kcal/mol. The 4a⇌ 4bexchange at 283 K is faster than that of the previously reported PMe3analogs W(CH2SiMe3)3(CSiMe3)(PMe3) (2a) ⇌ W(CH2SiMe3)2(CHSiMe3)2(PMe3) (2b).(1) The 4a⇌ 4bmixture undergoes an α-H abstraction, yielding alkyl alkylidene alkylidyne complexes W(CH2SiMe3)(CHSiMe3)(CSiMe3)(DMPE) (syn, 7a; anti, 7b) containing chelating DMPE ligand with the following activation parameters: ΔH2⧧= 13.2(1.3) kcal/mol and ΔS2⧧= −36(4) eu. The formation of 7a,bis faster than the formation of W(CH2SiMe3)(CHSiMe3)(CSiMe3)(PR3)2(PR3= PMe3, 5a,b; PMe2Ph, 6a,b). [ABSTRACT FROM AUTHOR]

This Account describes recent work in the development and applications of sol–gel sensors for concentrated strong acids and bases and metal ions. The use of sol–gel films doped with organic indicators for the optical sensing of concentrated strong acids (HCl, 1–10 M) and bases (NaOH, 1–10 M) has been explored, and the development of dual optical sensor approaches for ternary systems (HCl–salt–H 2O and NaOH–alcohol–H 2O) to give acid and salt, as well as base and alcohol, concentrations is discussed. The preparation of transparent, ligand-grafted sol–gel monoliths is also described, and their use in the analysis of both metal cations (Cu 2+) and metal anions [Cr(VI)] is presented. A new model using both metal ion diffusion and immobilization by the ligands in such monoliths has been developed to give metal concentrations using the optical monolith sensors. In addition to optical sensing, a method utilizing ligand-grafted sol–gel films for analyte preconcentration in the electrochemical determination of Cr(VI) has been explored and is discussed. [ABSTRACT FROM AUTHOR]