Primary amido substituted diborane4 compounds and imidodiborate4 anions

Treatment of the diborane(4) compound B(2)(NMe(2))(4) with aniline or 2,6-dimethylaniline results in the primary amido compounds B(2)(NHR)(4)(R = Ph, 2,6-Me(2)C(6)H(3)); subsequent treatment with n-BuLi in toluene in each case affords the first examples of anionic imidodiborates namely Li(4)(thf)(6)B(2)(NPh)(4) and Li(4)(thf)(4)B(2)(N-2,6-Me(2)C(6)H(3))(4); all complexes have been characterised crystallographically.     

Preparative isolation of (+)-beta-eudesmol fromAmyris balsamifera

Summary Optically pure (+)-beta-eudesmol is a possible starting material for the synthesis of several termite defense compounds. A two step procedure for the isolation of gram quantities of (+)-beta-eudesmol from commercially availableAmyris balsamifera oil (syn. West Indian sandalwood oil), containing 8% beta-eudesmol, was developed. Step one consisted of an efficient vacuum distillation of the total oil. Step two was a medium pressure LC separation with an AgNO₃ impregnated silica gel stationary phase. Several other separation procedures failed due to the presence of many closely related sesquiterpene alcohols (75% of the oil).     

Diastereotopic effect in some N-substituted-3-methyl-4,1-benzoxazepine-2,5-diones

1H NMR assignment of seven differently N-substituted-3-methyl-4,1-benzoxazepine-2,5-diones (I) revealed that with the exception of allyl, N-methylene protons of the substituents exhibit diastereotopy due to presence of a chiral centre in the heterocyclic ring at C-3. The significant finding is that the methylenes at C-2' in the substituents n-propyl and n-butyl (Id, Ie) also show diastereotopy. However, the one closer to the chiral centre (at C-1') exhibits greater non-equivalence of its protons. The diastereotopic methylene groups reported in this study correspond to the simplest system AB on one hand and as complex as ABMM'X2 or ABMM'X3 on the other. Calculated spectra obtained from assigned set of data for most of the coupled protons were in good agreement with the observed ones.     

Stabilization of Catalytically Active Cu+ Surface Sites on Titanium–Copper Mixed‐Oxide Films

The oxidation of CO is the archetypal heterogeneous catalytic reaction and plays a central role in the advancement of fundamental studies, the control of automobile emissions, and industrial oxidation reactions. Copper‐based catalysts were the first catalysts that were reported to enable the oxidation of CO at room temperature, but a lack of stability at the elevated reaction temperatures that are used in automobile catalytic converters, in particular the loss of the most reactive Cu⁺ cations, leads to their deactivation. Using a combined experimental and theoretical approach, it is shown how the incorporation of titanium cations in a Cu₂O film leads to the formation of a stable mixed‐metal oxide with a Cu⁺ terminated surface that is highly active for CO oxidation.     

The co-ordination chemistry of tris(3,5-dimethylpyrazolyl)methane manganese carbonyl complexes: synthetic, electrochemical and DFT studies

The tricarbonyl [Mn(CO)(3){HC(pz')(3)}][PF(6)] 1(+)[PF(6)](-) (pz' = 3,5-dimethylpyrazolyl) reacts with a range of P-, N- and C-donor ligands, L, in the presence of trimethylamine oxide to give [Mn(CO)(2)L{HC(pz')(3)}](+) {L = PEt(3)3(+), P(OEt)(3)4(+), P(OCH(2))(3)CEt 5(+), py 6(+), MeCN 7(+), CNBu(t)8(+) and CNXyl 9(+)}. The complex [Mn(CO)(2)(PMe(3)){HC(pz')(3)}](+)2(+) is formed by reaction of 7(+) with PMe(3). Complexes 2(+) and 6(+) were structurally characterised by X-ray diffraction methods. Reaction of 7(+) with half a molar equivalent of 4,4'-bipyridine gives a purple compound assumed to be the bridged dimer [{HC(pz')(3)}Mn(CO)(2)(μ-4,4'-bipy)Mn(CO)(2){HC(pz')(3)}](2+)10(2+). The relative electron donating ability of HC(pz')(3) has been established by comparison with the cyclopentadienyl and tris(pyrazolyl)borate analogues. Cyclic voltammetry shows that each of the complexes undergoes an irreversible oxidation. The correlation between the average carbonyl stretching frequency and the oxidation potential for complexes of P- and C-donor ligands is coincident with the correlation observed for [Mn(CO)(3-m)L(m)(η-C(5)H(5-n)Me(n))]. The data for complexes of N-donor ligands, however, are not coincident due to the presence of a node (and phase change) between the metal and the N-donor in the HOMO of the complex as suggested by preliminary DFT calculations.     

N2O Dissociation behind reflected shock waves

The dissociation of N₂O/Ar mixtures, with and withoutadded CO, has been studied by monitoring both infrared and ultraviolet emissions behind reflected shock waves. Initial temperatures ranged from 1850 to 2535°K, and the total concentrations were 1.94–2.40 × 10¹⁸ molecule/cm³. The infrared emission, corrected if necessary for CO, was observed to decay exponentially, and an apparent rate constant K_app was obtained. Addition of CO had no effect upon k_app and all the data can be described by the followingArrhenius parameters (in units of cm³/molecule.sec): log A=?9.31±0.12 and E_A=219.1±5.2 kJ/mole. Ultraviolet emission data, in runs with added CO, indicate that the atomic oxygen concentration reached a constant value at t < 600 μsec for T₀ > 2050°K. Numerical integration of the mechanism allowed comparison of calculated and observed parameters relating to both infrared and ultraviolet data. A consistent fit to these data was obtained with k₁=1.3×10^?9 exp (?238 kJ/RT) and k₂=k₃=1.91×10^?11 exp(?105 kJ/RT). The concentration of atomic oxygen produced by N₂O dissociation is shown to be a sensitive function of k₁ through k₃. Upper limits are also set for the rate constants of the following reactions:      

Computation of 3D queries for ROCS based virtual screens

Rapid overlay of chemical structures (ROCS) is a method that aligns molecules based on shape and/or chemical similarity. It is often used in 3D ligand-based virtual screening. Given a query consisting of a single conformation of an active molecule ROCS can generate highly enriched hit lists. Typically the chosen query conformation is a minimum energy structure. Can better enrichment be obtained using conformations other than the minimum energy structure? To answer this question a methodology has been developed called CORAL (COnformational analysis, Rocs ALignment). For a given set of molecule conformations it computes optimized conformations for ROCS screening. It does so by clustering all conformations of a chosen molecule set using pairwise ROCS combo scores. The best representative conformation is that which has the highest average overlap with the rest of the conformations in the cluster. It is these best representative conformations that are then used for virtual screening. CORAL was tested by performing virtual screening experiments with the 40 DUD (Directory of Useful Decoys) data sets. Both CORAL and minimum energy queries were used. The recognition capability of each query was quantified as the area under the ROC curve (AUC). Results show that the CORAL AUC values are on average larger than the minimum energy AUC values. This demonstrates that one can indeed obtain better ROCS enrichments with conformations other than the minimum energy structure. As a result, CORAL analysis can be a valuable first step in virtual screening workflows using ROCS.