Biomedical subjects
Publications and source records attributed to Mark R J Elsegood.
We report a novel, facile and asymmetric approach to both enantiomers of the indole alkaloid deplancheine from a readily available, nonracemic chiral template. The natural product and its antipode are isolated with >95% ee.
This paper provides evidence that the degree of aurophilic character and resulting solid state arrangement observed in (isocyanide)gold(I) halides is in part dependent on the nature of halide substituent. In particular, we report here the synthesis of a series of novel (isocyanide)gold(I) halides involving trimethylamine-isocyanoborane, an unusual 'zwitterionic' isocyanide that is comparable to the more familiar methyl isocyanide, but potentially more strongly Lewis basic. The reaction of chloro(dimethyl sulfide)gold(I) and the isocyanoborane species, (RNC)(R =(H3C)3NB(H)2), gives the novel crystalline adduct [(RNC)AuCl] (1). Treatment of 1 in an organic phase with aqueous KBr effected substitution of the chloride to give the bromide analogue [(RNC)AuBr] (2). The structures of 1 and 2 were determined by X-ray crystallography to be isostructural, consisting of a zigzag topology of chains of monomers, where adjacent gold(I) centres interact aurophilically. However, similar reaction of 1 with KI solution affords the unusual and unexpected compound, [(RNC)2Au][AuI2] (3). This iodide 3, is a linear chain polymer of alternating anion, cation units that is formed via ligand redistribution. The complexes 1-3 all fluoresce in the presence of UV light; the fluorescence of 3 being most prevalent at room temperature. The free trimethylamine-isocyanoborane ligand, the dimeric structures of compounds 1,2 and the thermodynamic stabilities of the dimers in the gas phase were studied by density functional and ab initio calculations at various levels of theory. The theoretical results are compared to the corresponding experimental data.
Investigations into the effects of the choice of anion on the hydrogen-bonding interactions between anions and metal-sulfimide cationic complexes have led to the study of three novel compounds. Hexakis(S,S-diphenylsulfimide)cobalt(II) diiodide S,S-diphenylsulfimide acetonitrile disolvate, [Co(C12H11NS)6]I2.C12H11NS.2C2H3N, crystallizes in the centrosymmetric space group P-1 with Z = 2. Six diphenylsulfimide ligands coordinate to the cobalt centre through their N atoms. Two iodide counter-ions hydrogen bond to the cation through N-H...I interactions, with N...I distances in the range 3.7302 (19)-3.8461 (19) A. One extra molecule of sulfimide is included in the asymmetric unit, regardless of the metal-ligand ratio used in the synthesis, and this sulfimide molecule also hydrogen bonds to one of the iodide counter-ions through one N-H...I hydrogen bond. The reaction of FeCl3.6H2O with S,S-diphenylsulfimide monohydrate yields hexakis(S,S-diphenylsulfimide)iron(III) trichloride, [Fe(C12H11NS)6]Cl3. The complex crystallizes in the centrosymmetric cubic space group Pa-3 and the asymmetric unit contains one-sixth of a formula unit. Two of the chloride anions each hydrogen bond to three sulfimide NH groups on opposite sides of the [Fe(Ph2SNH)6]3+ cation. The third chloride anion does not take part in any strong hydrogen bonding; instead it is surrounded by aromatic groups and is involved in C-H...Cl hydrogen bonds. The reaction of [Pt(Ph2SNH)4]Cl2 with I2 facilitates oxidation of the Pt(II) metal centre to Pt(IV), producing tetrakis(S,S-diphenylsulfimide)diiodoplatinum(IV) dichloride dichloromethane disolvate, [PtI2(C12H11NS)4]Cl2.2CH2Cl2. The crystal structure is centrosymmetric, with the elongated octahedral cationic complex situated on an inversion centre. The chloride anions are hydrogen bonded to the cation through N-H...Cl hydrogen bonds, with two cis NH groups hydrogen bonded to each anion. Strong hydrogen bonding within these three compounds is limited to N-H...halide hydrogen bonds between the cation and two anions, with a three-up/three-down arrangement of the NH groups in the first two compounds. The anions also 'cap' the NH groups in the third compound. In all three cases, the anions are also involved in weaker hydrogen bonds utilizing the plethora of relatively acidic aryl CH groups in the structures.
The title compound, (C30H25NPS)2[Pd2Br6] or (Ph3PNSPh2)2[Pd2Br6], was crystallized from the reaction of (Ph3PNSPh2)[BPh4] with (PPh4)2[Pd2Br6], giving a salt rather than the intended coordination complex [PdBr3(Ph3PNSPh2)]. The compound crystallizes in the non-centrosymmetric space group Cc with one complete formula unit in the asymmetric unit. One of the two independent cations is disordered. The geometry of the two cations is compared with that of the only previously crystallized example of this cation, viz. its [SbCl6]- salt [Reck et al. (1982). Chem. Ber. 115, 2981-2996]. The bond angles within the P-N-S triad in the two cations in the title compound are narrower than those observed in the literature example, while the S-N bond lengths are slightly longer in the title compound. The P-N bond length in the ordered cation shows excellent agreement with that determined by Reck and co-workers, but the P-N bond lengths are lengthened slightly in the disordered cation. Weak C-H...Br interactions create a three-dimensional network, with cations and anions alternating along the crystallographic c direction.
The reaction of Se(4)N(4) with (Bu(4)N)(2)[Pd(2)Br(6)] gives the title compound, (C(16)H(36)N)(2)[Pd(2)Br(6)(N(2)Se(2))], in good yield. The [Pd(2)(Se(2)N(2))Br(6)](2-) anion lies on an inversion centre, and therefore the asymmetric unit contains half a formula unit. The crystal structure confirms the coordination of the Se(2)N(2) unit to Pd through the N atoms, as previously assigned by IR spectroscopic analysis [Kelly, Slawin & Soriano-Rama (1997). J. Chem. Soc. Dalton Trans. pp. 559-562]. The title compound contains the longest Pd-N bond so far observed for such systems.
In an unprecedented transformation, amide ligands are found to attack the imine carbon centers of tridentate Schiff base ligands attached to tin. The process is reversible, and the resultant (masked) amide species can be exploited as latent single-site initiators for the controlled polymerization of rac-lactide.
Reaction of a solution of CuSO(4) and S,S'-diphenylsulfimide, Ph(2)SNH 1, with sodium salts of trimesic acid (H(3)tma) in MeOH gives the 2-D coordination network [Cu(3)(Ph(2)SNH)(6)(tma)(2)] in which each trimesate is bound to three copper centres. Addition of other solvents to the reaction mixture causes a change in the shape of the network. By this route, three forms have been prepared and characterised by X-ray crystallography. These include the known honeycomb, 2, and brick-wall, 3, motifs and a herringbone, 4, arrangement which is novel for transition metal-containing trimesate complexes. Key to the supramolecular isomerism observed is the ability of 1 to facilitate structural isomerism at copper(II) centres. In contrast to 2 in which the copper centres are square planar, 4 is analogous to an inter-allogon, with both planar and tetrahedral copper centres. Also prepared is a related complex which is composed of discrete units of three copper centres. These are further linked into a 2-D network by hydrogen bonds.
The first formation of a Nicholas carbocation through cleavage of a carbon-carbon sigma bond has allowed the preparation of highly substituted tetrahydrofurans in a formal dipolar cycloaddition reaction.
Vanadyl procatalysts bearing chelating aryloxide ligands are found to polymerise ethylene, in the presence of dimethylaluminium chloride, with (for this metal) exceptionally high activities.
Vanadium complexes containing bis(benzimidazole)amine ligands, upon activation by simple alkylaluminium reagents, give unusually robust, single-site, catalysts for olefin polymerisation/co-polymerisation.
The N,N-dimethylformamide (DMF) solvates of terephthalic acid, H(2)TA.2DMF (C(8)H(6)O(6).2C(3)H(7)NO), pyromellitic acid, H(4)PMA.4DMF (C(10)H(6)O(8).4C(3)H(7)NO), and hemimellitic acid, H(3)HMA.2DMF.H(2)O (C(9)H(6)O(6).2C(3)H(7)NO.H(2)O), are reported. The DMF solvate of terephthalic acid is centrosymmetric, containing one complete formula unit in the asymmetric unit. Both carboxylic acid groups hydrogen bond to a DMF molecule via an R(2)(2)(7) O-H.O/C-H.O motif. Discrete H(2)TA.2DMF units are observed. The DMF solvate of pyromellitic acid is centrosymmetric and the asymmetric unit contains half a formula unit. One of the unique carboxylic acid groups forms an R(2)(2)(7) motif with a DMF molecule, while the other forms a linear O-H.O hydrogen bond to the second unique DMF molecule. Discrete H(4)PMA.4DMF units are observed. The DMF solvate of hemimellitic acid is non-centrosymmetric and includes a molecule of water per formula unit. Both DMF molecules form an R(2)(2)(7) motif with the two outer carboxylic acid groups of HMA. A one-dimensional ladder structure is formed via hydrogen bonding between the central carboxylic acid group and the water molecules. The carboxylic acid R(2)(2)(8) head-to-tail motif is not observed in any of these examples. The inclusion of DMF thereby has the effect of limiting the dimensionality of the structures.
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The solid-state structure of the title compound, C19H15NS2, is unusual among substituted thiophene/pyrrole derivatives in that the molecular packing is dominated by pi-pi interactions between the benzyl substituents. This may be due to the large torsion angles observed between adjacent heterocycles. Torsion angles between adjacent rings in polypyrrole and polythiophene conducting polymers are related to conjugation length and the conductivity properties of the polymer materials. The title compound crystallizes in space group P21/c with two molecules in the asymmetric unit, both of which exhibit disorder in one of their thiophene rings.
The title compound, [Pb(C(8)H(4)O(4))(H(2)O)](n), forms as an insoluble product in the reaction of sodium terephthalate(2-) with Pb(NO(3))(2) in water. Analysis has shown that the crystal structure is centrosymmetric, with the asymmetric unit containing one formula unit. The lead geometry is hemidirected seven-coordinate, with both monodentate and bidentate carboxylate coordination modes present. The combination of hydrogen bonds and coordination bonds produces a three-dimensional structure, including the first example, in a lead complex, of the common metal-coordinated carboxylate/water R(1)(1)(6) graph-set motif.
The crystal structures of three complexes of dicarboxy-2,2'-bipyridyl ligands, 5,5'-dicarboxy-2,2'-bipyridyl (1) and 4,4'-dicarboxy-2,2'-bipyridyl (2) are reported. [Rh(1H)3] shows two interpenetrating, homochiral rhombohedral networks linked by short carboxylate-carboxylic acid hydrogen bonds, in which each complex acts as a node for six hydrogen bonds. [Ru(1H2)(1H)2] forms only four such hydrogen bonds, leading to the formation of heterochiral chains held together by stacking between bipyridyls. [Co(2H)3] can in principle form six hydrogen bonds, but in practice forms only four in a layer structure where stacking interactions are important. This is attributed to differences in molecular shape.
The reaction of CaCO3 with isophthalic acid in water yields nonaaquapenta-mu-isophthalato-pentacalcium octahydrate, [[Ca(5)(C(8)H(4)O(4))(5)(H(2)O)(9)].8H(2)O](n), a complex polymeric one-dimensional column structure bearing metal-carboxylate bonds and Ca-bound terminal and bridging water molecules, in addition to hydrogen-bonded water molecules of crystallization. The asymmetric unit comprises half of the formula unit, with one Ca(2+) ion located on a twofold axis, and contains 16 unique strong O-H.O hydrogen bonds, some of which link the columns together.
Structural determinations of the magnesium(II) and barium(II) salts of pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid) are presented. Hexaaquamagnesium(II) benzene-1,2,4,5-tetracarboxylate(2-), [Mg(H(2)O)(6)](C(10)H(4)O(8)), (I), and pentaaqua[benzene-1,2,4,5-tetracarboxylato(2-)]barium(II), [Ba(C(10)H(4)O(8))(H(2)O)(5)], (II), are both centrosymmetric and both possess a 1:1 metal-ligand ratio, but the two structures are found to differ in that the magnesium salt contains a hexaaqua cation and possesses only hydrogen-bonding interactions between cations and anions, while the barium salt exhibits coordination of the carboxylate ligand to the nine-coordinate metal centre. In (I), both ions sit on a 2/m site symmetry, and in (II), the cation and anion are located on m and i site symmetries, respectively.
Alkali metal salts of terephthalic acid are common reagents in the preparation of metal-ligand coordination complexes containing terephthalate anions. In the title compound, sodium hydrogen terephthalate, [Na(C(8)H(5)O(4))](n), the cations occupy crystallographic inversion centres, and each bridging anion coordinates to six octahedral cations and vice versa. As seen in the known potassium derivative [Kaduk (2000). Acta Cryst. B56, 474-485; Miyakubo, Takeda & Nakamura (1994). Bull. Chem. Soc. Jpn, 67, 2301-2303], sodium hydrogen terephthalate contains short O-H.O hydrogen bonds between anions [O.O = 2.4734 (17) A]. The structure is centrosymmetric and exhibits disorder of the H-atom position in the hydrogen bond and of the non-bridging ring C atoms in the terephthalate ion.