Palladium- and copper-catalyzed 1,4-additions of organozinc compounds to conjugated aldehydes

Conjugated aldehydes undergo smooth Pd(OAc)2.PPh3- or Me2CuCNLi2-catalyzed 1,4-addition of dialkylzinc reagents. [reaction: see text].     

A simple and rapid method for the determination of particle size in emulsions from ultrasound data

Oil droplet size in emulsions can be determined from ultrasound velocity and attenuation spectra. We show that explicit solutions of the acoustic scattering matrix may be used to rapidly calculate a mean particle size for a limited but useful range of particle sizes. Our technique is well suited to in-line measurement. Both modelling and experiment indicate that the main scattering mechanism is thermal scattering. Calculations using the explicit solutions have been compared with experimental results from sunflower oil-in-water emulsions.     

A structural study of dimethylaluminum carboxylato and hydrazonato complexes

The reaction of trimethylaluminum with 2,4,6-triphenylbenzoic acid and the isoelectronic fluoren-9-one phenylhydrazone results in the formation of the dialkylaluminum complexes [(CH₃)₂Al{μ-O₂CPh(Ph₃)}]₂ (4) and [Me₂AlN(C₆H₅)NC₁₃H₈]₂ (5). The synthesis of these complexes, as well as their spectroscopic and structural characterization are reported. X-ray crystallographic studies show that the carboxylato complex 4 adopts a dimeric structure containing an 8-membered O-Al-O-C core whereas the hydrazonato complex 5 likewise is dimeric in the solid state, but exhibits a 6-membered N-Al-N heterocyclic ring.     

The crystal structures of 2-(2′-pyridyl)phenyltellurium(II) bromide and of the inclusion compound bis[2-(2′-pyridyl)phenyltellurium(II) chloride]·p-ethoxyphenyl-mercury(II) chloride

In 2-(2′-pyridyl)phenyltellurium(II) bromide (1) the coordination about tellurium may be described as pseudo-trigonal bipyramidal wth bromine (Te---Br = 2.707(11) Å) and nitrogen (Te---N) = 2.236(11) Å) atoms occupying axial positions. The equatorial plane comprises a carbon atome (Te---C = 2.111(6) Å) and two lone pairs of electrons. There are no significant intermolecular interactions between the six independent molecules in the unit cell. Bis[2-2′-pyridyl)phenyltellurium(II) chloride]·p-ethoxy-phenylmercury(II) chloride (2) may be regarded as an “inclusion compound” obtained by replacement of two RTeX (X = Cl or Br) molecules by two p-ethoxyphenylmercury(II) chloride entities. There is approximately linear coordination about mercury (C---Hg---Cl = 179.2°(4), Hg-C = 2.044(14) and Hg---Cl = 2.328(4) Å) and 2-(2′-pyridyl)phenyltellurium(II) chloride, with a structure similar to that of (1) above (Te---N = 2.2366(6), Te---Cl = 2.558(1), Te---C = 2.080(25) Å). There are no significant intermolecular contacts.     

Thiocyanato adducts of chromium(II) carboxylates and the molecular structure of tetraethyl-ammonium tetra-μ-propionatodiisothio-cyanatodichromate(II)

X-Ray crystallographic studies on [NEt₄]₂[Cr₂[(O₂CC₂H₅)₄(NCS)₂] show that the Cr–Cr separation (2.467Å) in the dinuclear anion is one of the longest known. The thiocyanato groups are N-bonded, and the results emphasize the known sensitivity of the quadruple Cr–Cr bond to the nature of the axial ligands. The compound crystallises in the tetragonal space group P4/mnc with two molecules per unit cell, the dimensions of which are a = b = 9.785(1), c = 21.186(2) Å. Magnetic investigations from room to liquid nitrogen temperature on the tetra-μ-propionato complex and on [NMe₄]₂ [Cr₂(O₂CCH₃)₄(NCS)₂] show that both complexes have been obtained free from paramagnetic chromium(III) impurities. Their weak paramagnetic susceptibilities (X_cr is approx. 200 x 10⁻⁶ cm³ mol⁻¹ at 295 K and 50 x 10⁻⁶cm³mol⁻¹ at 90 K) are inherent, and are ascribed to temperature independent paramagnetism at low temperature plus para-magnetism arising from slight population of the triplet state (2J 700 cm⁻¹, g = 2, N = 50 x 10⁻⁶cm³mol⁻¹) at higher temperatures.     

Structural and conformational studies of derivatives of 2,4,8-trihydroxy-5-oxo-10-methylbenzo[1,2-c]chromene (alternariol). II: Crystal and molecular structure of (±)-1-methoxycarbonyl-1-hydroxy-2-oxa-3,4-dioxo-7-methoxy-9-methylcyclopenteno [3,4-c]chromene

The crystal and molecular structure of (±)-1-methoxycarbonyl-1-hydroxy-2-oxa-3,4-dioxo-7-methoxy-9-methylcyclopenteno[3,4-c] chromene (Altox, II) has been determined by x-ray crystallographic methods. The crystals are monoclinic:a= 10.748,b = 9.644,c= 13.845 Å, = 104.58 °,Z = 4,P2₁/c. The structure was solved by direct methods and refined by full-matrix least-squares on 1158 symmetry-independent ¦F ₀¦-data toR = 6.9%. The molecules are linked by hydrogen bonds (O...O = 2.74 Å), forming a chain-like structure.     

Structures of NN′-ethylenebis(monothioacetylacetoneiminato)nitrosylcobalt and NN′-ethylenebis(2-hydroxyacetophenoneiminato)nitrosylcobalt

The cobalt atoms in both [Co(NO)(sacacen)] and [Co(NO)(7-Mesalen)] {sacacenH₂ isNN-ethylenebis(monothioacetylacetoneimine) and 7-MesalenH₂ isNN-ethylenebis(2-hydroxyacetophenoneimine)} are 5-coordinate, with a tetragonal-pyramidal arrangement of donor atoms. The cobalt atom in [Co(NO)(sacacen)] lies just above the plane defined by the SNNS donor atoms of the quadridentate ligand, and the nitrosyl group occupies the apical position. A similar geometry is defined by the ONNO donor atoms and the NO group in [Co(NO)(7-Mesalen)]. The Co-N-O angles are strongly bent, as predicted from¹⁵N-nmr studies (127.2(6)°[Co(NO)(sacacen)] and 127.4(3)°[Co(NO)(7-Mesalen)]). Both nitrosyls crystallize in the monoclinic system. For [Co(NO)(sacacen)],a=8.501,b=12.673,c=13.866 Å,=95.00°,Z=4 and space groupP2₁/c. The structure was determined by the heavy-atom method, usingMo K diffractometer data, and refined by full matrix least squares toR=0.062 for 2920 observed reflections. For [Co(NO)(7-Mesalen)],a=9.461,b=13.053,c=13.456,=99.32°,Z=4 and space groupP2₁/c. The structure was determined as above toR=0.040 for 2461 observed reflections.     

Matrix-assisted laser desorption/ionization-collision induced dissociation of poly(styrene)

Matrix-assisted laser desorption/ionization-collision induced dissociation (MALDI-CID) has been employed for the analysis of poly(styrene) in a tandem hybrid sector-time of flight instrument. Spectra are shown for adducts of poly(styrene) with copper and silver ions. The distributions of fragment ion peaks were found to be consistent from precursor ions containing both metal ions. It is shown how the masses of the end groups of the polymer may be inferred from the mass-to-charge ratios of two of the series of ion peaks that are seen in the MALDI-CID spectra. Mechanisms are proposed for the formation of some of the other series of ion peaks that are observed in the spectra.