Ann M. Chippindale

Enantioselective Intramolecular Michael Addition of Nitronates onto Conjugated Esters: Access to Cyclic γ-Amino Acids with up to Three Stereocenters

A highly stereoselective synthesis of conformationally constrained cyclic gamma-amino acids has been devised. The key step involves an intramolecular cyclization of a nitronate onto a conjugated ester, promoted by a bifunctional thiourea catalyst. This methodology has been successfully applied to generate a variety of gamma-amino acids, including some containing three contiguous stereocenters, with very high diastereoselectivity and excellent enantioselectivity. It is postulated that an interaction that is key to the success of the process is the simultaneous coordination of the thiourea functionality to both the conjugated ester and the nitronate. Finally, the synthetic utility of these compounds is demonstrated in the synthesis of two dipeptides derived from the C- and N-termini.

Asymmetric synthesis of cyclic β-amino acids and cyclic amines via sequential diastereoselective conjugate addition and ring closing metathesis

Abstract Diastereoselective conjugate addition of lithium (S)-N-allyl-N-α-methylbenzylamide to a range of α,β-unsaturated esters followed by ring closing metathesis is used to afford efficiently a range of substituted cyclic β-amino esters in high d.e. Alternatively, conjugate addition to α,β-unsaturated Weinreb amides, functional group conversion and ring closing metathesis affords cyclic amines in high d.e. The further application of this methodology to the synthesis of a range of carbocyclic β-amino esters via conjugate addition, enolate alkylation and ring closing metathesis is also described. Application of this methodology affords, after deprotection, (S)-homoproline, (S)-homopipecolic acid, (S)-coniine and (1S,2S)-trans-pentacin.

Chemical characterisation and superconductivity of two phases in the BiSrCaCuO system

Abstract We have identified two superconducting phases within the BiSrCaCuO system and determined their stoichiometries as Bi(Sr, Ca) 1.33CuOx(Tonset ≈ 98 K) and Bi2(Sr, Ca) 1.5CuOx(Tonset ≈ 98 K) using high-resolution analytical electron microscopy. The pseudo-tetragonal unit cells, determined from powder X-ray data, are a = 3.8206(7) A , c = 30.78(2) A and a = 3.8008(9) A , c = 24.500(4) A , respectively. Their structures appear to be closely related and possible structural motifs are proposed.

CoGaPO-5: Synthesis and crystal structure of (C6N2H14)2[Co4Ga5P9O36], a microporous cobalt-gallium phosphate with a novel framework topology

A microporous cobalt-gallium phosphate, (C6H14N2)2[Co4Ga5P9O36], has been synthesized under solvothermal conditions and the structure determined at 293 K by single-crystal X-ray diffraction (monoclinic, I 2/a, a = 15.002(2), b= 17.688(2), c= 15.751(2) A, β = 97.24(1)∘, V= 4146.3 A3, Z= 4). The framework of this material is constructed from alternately linked MO4 (M = Co or Ga) and PO4 tetrahedra, and it has a topology unlike that of any previously reported material. The DABCO template occupies sites within 2-dimensional intersecting networks of pores, which are surrounded by 8- and 10-membered rings. The structure has been approved by the Structure Commission of the International Zeolite Association and given the code CGF.

A reactive template in the synthesis of a novel layered aluminium phosphate (Al3P4O16)3–[NH3(CH2)5NH3]2+(C5H10NH2)+

Starting from 1,5-diaminopentane as template it is possible to produce a novel microporous layered aluminophosphate (Al:P = 0.75) in which there are two distinct kinds of eight-membered rings within the layers: those that are approximately circular (diameter 7.0 A) accommodate piperidinium ions, while the elliptical ones (ca. 5.9–8.0 A) contain 1,5-diammoniumpentane ions.

New molecular lanthanide materials for organic electroluminescent devices

Organic electroluminescent (EL) devices based upon the new lanthanide EL material Tb[Ph2P(O)NP(O)Ph2]3 (Tbpip3) are described. Several device structures are reported and the effect of charge transporting material and layer thickness on device performance critically assessed. Device performance is optimised in a three-layer structure containing TPD and Alq as the charge transport layers. This device has an efficiency of 0.7 cd A−1 at 20 cd m−2 at 25 V and 1 mA cm−2.

Synthesis and characterisation of transition-metal-substituted gallium phosphates with the laumontite structure

Three novel metal-substituted gallium phosphates, (C3N2H5)8[Me8Ga16P24O96] (Me = Co, Fe, Mn), have been synthesised under solvothermal conditions and their structures determined using single-crystal X-ray diffraction. They are isostructural, with monoclinic symmetry, space group C 2/c and unit-cell dimensions ca. 15 × 13 × 15 A, β ca. 111°. The materials all have frameworks with the laumontite topology (structure type code LAU), constructed from alternating PO4 and MO4 tetrahedra (M = Me and Ga) with imidazole cations occupying sites within the channels of the framework. Magnetic susceptibility measurements show that the materials exhibit Curie-Weiss behaviour over wide ranges of temperature and that the transition metals are present as divalent cations.

The relationship between chemical composition and superconductivity in the Tl-Ba-Ca-Cu-O Superconductors

Abstract A careful examination of the compositions of superconducting phases in the Tl-Ba-Ca-Cu-O system has been carried out by high-resolution analytical electron microscopy. The phases containing two thallium layers, previously reported as Tl 2 Ba 2 CaCu 2 O 8 and Tl 2 Ba 2 Ca 2 Cu 3 O 10 , are found to be both calcium and, apparently, thallium deficient, with compositions close to Tl 1.76 Ba 2.0 Ca 0.70 Cu 2 O 8 and Tl 1.83 Ba 2.0 Ca 1.44 Cu 3 O 10 , respectively. Our results for the one-layer phase, reporte d as TlBa 2 Ca 2 Cu 3 O 9 , confirm that this stoichiometry is essentially correct. These findings are discussed in relation to the oxidation state of copper in the three cases.

Solvothermal synthesis and structural characterisation of the first ammonium cobalt gallium phosphate hydrate, NH4[CoGa2P3O12(H2O)2]

The first ammonium cobalt gallium phosphate hydrate, NH4[CoGa2P3O12(H2O)2] has been prepared under solvothermal conditions and the structure determined using single-crystal X-ray diffraction [space group C2/c, a= 13.323(3), b= 10.245(1), c= 8.886(2)A, β= 108.43(2)°, V= 1150.68 A3, Z= 4]. The structure consists of GaO5, CoO6 and PO4 polyhedra linked to form a microporous three-dimensional framework containing channels in which the NH4+ cations reside.

A novel “126” phase of the family of Y2Ba4Cu6+nO14+n high-temperature superconducting materials

Abstract Following our work on lithium insertion into YBa 2 Cu 3 O 7− δ (commonly referred to as “123”) in which we observed the room-temperature formation of YBa 2 Cu 4 O 8 (“124”) [1,2], we have now found, by the same procedure using “124” as starting material, a novel phase with Y:Cu:Ba in the ratio 1:2:6 (“126”), intergrown in different proportions with YBa 2 Cu 4 O 8 and YBa 2 Cu 5 O 9 (“125”). Powder X-ray diffraction patterns and electron microscopy and diffraction suggest a unit cell of ≈ 3.80 × 3.86 × 33.4 A containing four [CuO 4 ] chain layers instead of the two observed in the original “124”.