Dehydrative thiolation of allenols: indium vs gold catalysis.

Intermolecular additions of thiols to allenols via formal S(N)2' selectivity to produce functionalized dienes are described. Although this dehydrative reaction was initially developed using gold(I) catalysis, indium(III) proves to be a far superior catalyst in terms of selectivity and substrate scope.

THE PHYSICAL AND CHEMICAL MICROSTRUCTURE OF THE ACHATINA FULICA EPIPHRAGM.

Microstructural characterization of Achatina fulica Bowdich, 1822 epiphragms and mucus secretions was performed to address two questions: what are the structure and composition of the reinforcing inorganic phase in the epiphragms, and what enables a durable epiphragm to form quickly in comparison to other biomineralized materials? Characterization was performed by a combination of light microscopy (relying on a variety of contrast modes), wet chemical tests, environmental scanning electron microscopy (including the use of energy dispersive X-ray analysis to obtain compositional data), and X-ray diffraction. The morphology of the inorganic phase promotes mechanical interlocking and presents a large surface for binding to the organic matrix. Strong binding occurs between the organic and inorganic phases. The inorganic phase adopts the calcite structure; its composition is Ca(0.912) Mg(0.088) CO(3). Epiphragms can form quickly because pre-grown crystals of the inorganic reinforcing phase are co-deposited with the mucus matrix. Unlike other biomineralized material, the crystals are not solution-grown in situ on an organic template in the final product.

New chemistry of 1,2-closo-P2B10H10 and 1,2-closo-As2B10H10; in silico and gas electron diffraction structures, and new metalladiphospha- and metalladiarsaboranes.

The molecular structures of 1,2-closo-P(2)B(10)H(10) (1) and 1,2-closo-As(2)B(10)H(10) (2) have been determined by gas electron diffraction and the results obtained compared with those from computation at the MP2/6-31G** level of theory. The level of agreement is good for 2 (root-mean-square [rms] misfit for As and B atoms 0.0297 Å) and very good for 1 (rms misfit for P and B atoms 0.0082 Å). In comparing the structures of 1 and 2 with that of 1,2-closo-C(2)B(10)H(12) (I) it is evident that expansion of the polyhedron from I to 1 to 2 is restricted only to the heteroatom vertices and the B(6) face to which these are bound. Following deboronation (at B3) and subsequent metallation, compounds 1 and 2 have been converted into the new metalladiheteroboranes 3-(η-C(9)H(7))-3,1,2-closo-CoAs(2)B(9)H(9) (4), 3-(η-C(10)H(14))-3,1,2-closo-RuAs(2)B(9)H(9) (5), 3-(η-C(5)H(5))-3,1,2-closo-CoP(2)B(9)H(9) (6), 3-(η-C(9)H(7))-3,1,2-closo-CoP(2)B(9)H(9) (7) and 3-(η-C(10)H(14))-3,1,2-closo-RuP(2)B(9)H(9) (8), the last three constituting the first examples of metalladiphosphaboranes. Together with the known compound 3-(η-C(5)H(5))-3,1,2-closo-CoAs(2)B(9)H(9) (3), compounds 4-8 have been analysed by NMR spectroscopy and (except for 8) single-crystal X-ray diffraction. The (11)B NMR spectra of analogous pairs of metalladiphosphaborane and metalladiarsaborane (6 and 3, 7 and 4, 8 and 5) reveal a consistently narrower (9-10 ppm) chemical shift range for the metalladiarsaboranes, the combined result of a deshielding of the lowest frequency resonance (B6) and an increased shielding of the highest frequency resonance (B8) via an antipodal effect. In crystallographic studies, compounds 3 and 5B (one of two crystallographically-independent molecules) suffer As/B disorder, but in both cases it was possible to refine distinct, ordered, components of the disorder, the first time this has been reported for metalladiarsaboranes. Moreover, whilst the Cp compounds 6 and 3 are disordered, their indenyl analogues 7 and 4 are either ordered or significantly less disordered, a consequence of both the reduced symmetry of an indenyl ligand compared to a Cp ligand and the preference of the former for a distinct conformation relative to the cage heteroatoms. Unexpectedly, whilst this conformation in the cobaltadiphosphaborane 7 is cis-staggered (similar to that previously established for the analogous cobaltadicarborane), in the cobaltadiarsaborane 4 the conformation is close to cis-eclipsed.

7,8-Diphenyl-9-dimethylsulfido-10,11-mu-hydro-7, 8-dicarba-nido-undecaborane(9).

In the title compound, C(16)H(25)B(9)S, there are two crystallographically independent molecules, and the conformations of the phenyl and SMe(2) substituents indicate some intramolecular steric crowding. The bridging H atom is asymmetrically disposed. The title compound is a precursor to a crowded vertex-labelled nido carborane ligand important in establishing the mechanism of isomerization of icosahedral heteroboranes.

Sodium hydrogen bis(phenoxyacetate).

In the title compound, Na(+) x H(+) x [2C(8)H(7)O(3)](-), the anion contains a short Speakman-type hydrogen bond [O...O = 2.413 (2) A]. The anions and the Na atoms lie across twofold axes.

Sodium phenoxyacetate hemihydrate.

The structure of the hemihydrate of sodium phenoxyacetate, Na(+) x C(8)H(7)O(3)(-) x 0.5H(2)O, has been redetermined at low temperature (160 K). The structure consists of ribbons containing octahedral NaO(6) units, and half of the Na(2)O(2) squares within the ribbon are bridged by water molecules which lie across twofold rotation axes in C2/c. The phenyl substituents lie on the outside of the ribbon.

Crystal engineering with heteroboranes. I. 1-Carboxy-1,2-dicarba-closo-dodecaborane(11).

The title compound, C(3)H(12)B(10)O(2) or 1-COOH-1,2-closo-C(2)B(10)H(11), forms centrosymmetric dimers through intermolecular hydrogen bonding between the carboxylic acid groups, resulting in the formation of an eight-membered ring [R(2)(2)(8)]. The C==O bond of the carboxylic acid group almost eclipses the unsubstituted cage C atom, with a C-C-C-O torsion angle of 2.6 (2) degrees.

Are halocarboranes suitable for substitution reactions? The case for 3-I-1,2-closo-C(2)B(10)H(11): molecular orbital calculations, aryldehalogenation reactions, (11)B NMR interpretation of closo-carboranes, and molecular structures of 1-Ph-3-Br-1,2-closo-C(2)B(10)H(10) and 3-Ph-1,2-closo-C(2)B(10)H(11).

In this paper, the chemistry of 3-X-1,2-closo-C(2)B(10)H(11) (X = halogen) derivatives is extended. Molecular orbital and (11)B and (13)C NMR calculations on these species are presented. A qualitative interpretation of the (11)B NMR spectra of closo o-carborane derivatives is also provided. The synthesis of 3-X-1-R-o-carborane (X = I, Br and R = Me, Ph) derivatives is reported, and aryldehalogenation at the B3 position is reported for the first time. The molecular and crystal structures of 1-phenyl-3-bromo-1,2-dicarba-closo-dodecaborane and 3-phenyl-1,2-dicarba-closo-dodecaborane are described.