W. Errington

Polyphenols and alkaloids from piper species

Abstract Thirty eight compounds of different types have been isolated from twelve Piper species. The ether extract of the leaves of P. aduncum yielded eleven compounds, out of which 2,6-dimethoxy-4-(2-propenyl)phenol was isolated for the first time from the genus Piper and 2-acetoxy-1,3-dimethoxy-5-(2-propenyl)benzene is a new compound. The petrol extract of the stems and leaves of P. attenuatum furnished a novel long chain alcohol, 14-benzo 1 , 3 dioxol-5-yl-tetradecan-2-ol. From P. betle, β-sitosteryl palmitate was isolated for the first time from the genus Piper. A novel amide, 3-(3,4-dimethoxyphenyl)propanoyl pyrrole has been obtained from P. brachystachyum. Nerolidol was isolated for the first time from P. falconeri. From the methanol extract of the stems and leaves of P. khasiana, piperlonguminine, piperine, apigenin dimethyl ether and β-sitosterol were obtained. Retrofractamide A was obtained for the first time from P. longum; the structure of (+)-asarinin, isolated from P. longum, was confirmed by X-ray crystallographic studies. Retrofractamide A, apigenin dimethyl ether, tetratriacontanol and tectochrysin were isolated from P. manii. P. pedicellosum furnished β-sitosterol, pellitorine, piperlonguminine, cepharadione A and furacridone, the last compound being isolated for the first time from the genus Piper.

A Facile Synthesis of Novel Spiro- [Indole-pyrazolinyl-thiazolidine]-2,4′-dione

Abstract A reaction of appropriate indol-2,3-diones with 4-aminoantipyrine has resulted in the formation of hitherto unknown 3-(2,3-dimethyl-5-oxo-1-phenyl-3-pyrazolin-4-yl-imino)-indol-2-ones in quantitative yields which upon cyclocondensation with mercaptoacetic acid afforded a series of new spiro heterocycles 3′-(2,3-dimethyl-5-oxo-1-phenyl-3-pyrazolin-4-yl) spiro[3H-indol-3,2′-thiazolidine]-2,4′-diones.

An inexpensive approach to supramolecular architecture

A new approach to generating supramolecular architectures, based on inexpensive and easy-to-prepare imine ligands, is described together with its application to the self-assembly of supramolecular triple-helicates.

Coordination polymers based on octacyanometalates(IV,V)(M = Mo, W) and aliphatic polyamine copper(II) tectons with [N3] donor atom sets

The cyano-bridged [CuII(tetrenH2)]2[WIV(CN)8]2·5H2O (tetren = tetraethylenepentaamine) (1), [CuII(tetrenH2)][CuII(tetrenH)][WV(CN)8][WIV(CN)8]·2.5H2O (2), [CuII(dien)]2[WIV(CN)8]·4H2O (dien = diethylenetriamine) (3) and its isomorphous molybdenum(IV) analogue (4) have been prepared and structurally characterised. 1 and 2 are built from the W2Cu2(μ-CN)4 squares extended into 1-D structure by cyano-bridges. 2-D 3 and 4 form a square grid pattern with tungsten atoms in the corners and –CN–Cu(dien)–NC– linkages on the edges of the squares. The magnetic behaviour of 1 and 3 indicates the presence of two isolated CuII spins S = 1/2 with a very weak antiferromagnetic coupling through the diamagnetic NC–WIV–CN bridges in the low temperatures. Assembly 2 exhibits a weak ferromagnetic interaction between CuII and WV isolated by diamagnetic [WIV(CN)8]4− spacer from another CuII centre within WV–CN–CuII–NC–WIV–CN–CuII unit and the antiferromagnetic interaction between the CuII2WVWIV units.

Back bonding without σ-bonding: a unique π-complex of dinitrogen with uranium

The synthesis, molecular structure, spectroscopic properties and bonding in a complex of dinitrogen with trivalent uranium are described. The molecule has a side-on U–N2–U core which is supported by U N2 donation with no significant N2U bonding. Steric compression between the spectator triamidoamine ligands prevents the uranium atoms from approaching the N2 ligand at the optimum distance for overlap, and thus the N–N distance is not displaced significantly from that in gaseous dinitrogen.

Helical (isotactic) and syndiotactic silver(I) metallo-supramolecular coordination polymers assembled from a readily prepared bis-pyridylimine ligand containing a 1,5-naphthalene spacer.

A ligand in which two pyridylimine binding units are linked by a 1,5-naphthalene spacer is prepared and its silver(I) coordination chemistry investigated. In the solid state, a pair of C-H triplebond N interactions between pyridylimine units link the free ligands into chain structures, with further C-H triplebond N and some -stacking interactions linking these chains into a three-dimensional structure. The spacer constrains the ligand to dinucleate, and with silver(I) the metal coordinates to two pyridylimine units from two separate ligands and this leads to the formation of coordination polymers with a range of different anions. Different twisting motifs within the ligand control the tacticity of these coordination polymers and both isotactic, helical polymers and syndiotactic (achiral) polymers result. The core of the isotactic polymer strands contains two metallo-vectors and results in long-range ordering of the metal centres into a 2 x n grid arrangement. The solution behaviour indicates that exchange between the diastereomeric forms occurs. Since this must involve inversion at the metal centres, atactic species may also form a component of the solution library.

Ge(IV)–citrate complex formation: synthesis and structural characterisation of GeCl4(bipy) and GeCl(bipy)(Hcit) (bipy=2,2′-bipyridine, H4cit=citric acid)

Abstract The adduct [GeCl4(bipy)] (I), obtained by direct treatment of the parent halide with 2,2′-bipyridine (bipy), reacts with citric acid (H4cit) in acetonitrile solution to provide the chelate derivative [GeCl(bipy)(Hcit)] (II). The structures of compounds I and II have been determined by single crystal X-ray diffraction. For I the central germanium shows octahedral geometry with two mutually cis-chlorine atoms, GeCl (mean) 2.244(1) A, and the bidentate ligand, GeN (mean) 2.065(4) A occupying equatorial positions and two mutually trans-chlorine atoms, GeCl (mean) 2.267(1) A in axial locations. For II the citrate ligand is terdentate and bound to the central germanium via its hydroxyl, α-carboxylate and one of the β-carboxylate groups in a fac-octahedral arrangement. GeOhydroxyl 1.800(3) A, GeOcarboxylate (mean) 1.904(3) A, GeCl 2.209(1) A, GeN (mean) 2.012(3) A. The uncoordinated β-carboxylate group remains intact as a ‘dangling arm’. The structure also contains poorly defined and disordered acetonitrile (solvent) molecules trapped in the lattice.

Synthesis of di-, tri- and penta-nuclear titanium(IV) species from reactions of titanium(IV) alkoxides with 2,2′-biphenol (H2L1) and 1,1′-binaphthol (H2L2); crystal structures of [Ti3(μ2-OPri)2(OPri)8L1], [Ti3(OPri)6L13], [Ti5(μ3-O)2(μ2-OR)2(OR)6L14](R = OPri, OBun) and [Ti2(OPri)4L22]

Reaction of titanium(IV) alkoxides [Ti(OR)4] (R = OPri, OBun) with 2,2′-biphenol [C12H8(OH)2, H2L1] affords two trinuclear species [Ti3(OPri)10L1] and [Ti3(OPri)6L13] each possessing an open-chain V-shaped arrangement of three titanium atoms with the former having both bridging alkoxide and biphenylate groups and the latter having only biphenylate as bridging groups. Variations in reaction conditions yield the pentanuclear species [Ti5(μ3-O)2(OR)8L14] (R = OPri, OBun) which have two central bridging oxygen atoms in the Ti5 framework and bridging alkoxide and biphenylate groups. In contrast 1,1′-binaphthol [C24H12(OH)2, H2L2] yields the dinuclear [Ti2(OPri)4L22] where only the binaphthylate ligands act as bridging groups. Some of the compounds show catalytic activity in esterification reactions.

Inter- versus Intramolecular C−H Activation: Synthesis and Characterization of a Novel Platinum–Carbene Complex

13 C NMR spectroscopy as well as the short bond between the platinum and the C4 atom of the pyridine ring in 1 (1.95 Å) indicate the formation of a novel carbene species. Compound 1 is remarkably stable (m.p. 246°C), probably due to the presence of intramolecular hydrogen bonds, and is formed instead of the expected cyclometalated product. R=n-hexyl.

Synthesis of E- and Z-Pyrazolylacrylonitriles and their evaluation as novel antioxidants

A facile synthesis of (Z)- and (E)-2-(5-arylpyrazol-3-yl)-3-(pyrrol-2-yl)acrylonitriles and (Z)-2-(1,3-diarylpyrazol-5-yl)-3-pyrrol-2-yl)acrylonitriles, and isomerisation of (Z)-2-(5-arylpyrazolyl)acrylonitriles to (E)-2-(5-arylpyrazolyl)acrylonitriles under basic conditions have been reported. (Z)-2-(1,3-Diarylpyrazolyl)acrylonitriles did not undergo isomerisation under the similar conditions. New compounds were identified on the basis of their spectral data (1H-, 13C-, 1H-1H COSY, NOESY, NOE, HMQC NMR, IR, UV and EI mass). The structures of one acrylonitrile and five of their precursor 6-arylpyran-2-ones and cyanomnethylpyrazoles were confirmed by X-ray crystallographic studies. Effects of pyrazolylacrylonitriles and their precursors on rat liver-microsomal lipid peroxidation were evaluated in vitro with a view to establish structure activity relationship and to identify a lead compound.