Synthesis of sulfur containing dihydro-pyrrolo derivatives and their biological evaluation as antioxidants.

The 1,3-dipolar cycloaddition to N-phenylmaleimide of azomethine ylides, generated in situ from sulfanyl-substituted imines of glycine esters, yields 5H-dihydro-pyrrolo products with syn diastereoselectivity. The syn (major) and anti (minor) products were isolated chromatographically and fully characterized by spectroscopic methods and in two cases also by X-ray analysis. The diastereomeric cycloadducts were tested for their antioxidant activity with good results.

A structural and spectroscopic investigation of the hydrochlorination of 4,4'-methylenedianiline.

The hydrochlorination of 4,4'-methylenedianiline, NH(2)C(6)H(4)CH(2)C(6)H(4)NH(2) (MDA), in chlorobenzene to produce 4,4'-methylenedianiline dihydrochloride, [H(3)NC(6)H(4)CH(2)C(6)H(4)NH(3)]Cl(2) (MDA x 2 HCl) is an important reaction for the production of isocyanates, which are used to manufacture polyurethanes. This reaction is examined here. MDA is moderately soluble in chlorobenzene, whereas MDA x 2 HCl is effectively insoluble. Controlled addition of anhydrous HCl to MDA in chlorobenzene led to the isolation of a solid whose stoichiometry is MDA x HCl. Crystals obtained from solutions of MDA x HCl in methanol were found by X-ray analysis to consist of the basic hydrochloride salt, [MDAH(2)][Cl](2)[MDA](2)H(2)O, which is stabilised by complex hydrogen-bonding. The starting material MDA has an H-bonded structure in which the molecules are linked in a one-dimensional chain. Hydrogen-bonding is extensive in MDA x 2 HCl which contains ladders of [H(3)NC(6)H(4)CH(2)C(6)H(4)NH(3)](2+) dications stabilised by N-H...Cl linkages. Energy calculations on the crystalline systems allow an identification of the main factors in intermolecular cohesion; these are related to melting temperature and solubility data. Such improvements in understanding of solute-solute interactions are prerequisites for improving the atom economy of this important stage within the polyurethane manufacture process chain. The solid phase IR spectrum of MDA x 2 HCl is diagnostic, principally as a result of a Fermi resonance process.

Switching between novel samarium(II)-mediated cyclizations by a simple change in alcohol cosolvent.

Gamma,delta-unsaturated ketones undergo two very different stereoselective cyclization reactions mediated by samarium(II) iodide depending upon the alcohol cosolvent used in the reaction. Switching between an unprecedented aldol spirocyclization and a novel cyclobutanol-forming process can be achieved simply by changing the alcohol cosolvent from methanol to tert-butyl alcohol. [reaction: see text]

A structural and spectroscopic investigation of the hydrochlorination of 4-benzylaniline: the interaction of anhydrous hydrogen chloride with chlorobenzene.

The hydrochlorination of 4-benzylaniline in chlorobenzene to produce 4-benzylaniline hydrochloride has been examined. This has required spectroscopic and computational analysis of the solvation of gaseous HCl in the process solvent. The characterisation of the reagent and product of the hydrochlorination reaction by various techniques, including FTIR and (1)H NMR spectroscopy and X-ray diffraction, is described. The infrared spectrum of the hydrochloride salt contains a strong Fermi resonance interaction, readily distinguishing it from that of the starting material. Using the structural results as a basis, the lattice energies of reagent and product have been evaluated by the recently developed PIXEL method. This method allows the contributions of specific intermolecular interactions to the total lattice energy to be assessed and, in this case, tentatively correlated with solubility measurements.

(eta5-cyclopentadienyl)(N,N-dimethyldithiocarbamato-kappa2S,S')[eta4-tetrakis(trifluoromethyl)cyclobutadienyl]molybdenum(IV).

The title complex, [Mo(C8F12)(C5H5)(C3H6NS2)], contains both a eta4-C4(CF3)4 cyclobutadienyl ligand with approximate C4v local symmetry and a eta5-C5H5 cyclopentadienyl ring. The centroids of the rings and the S atoms of a chelating dithiocarbamate ligand define the pseudo-tetrahedral coordination of the Mo atom. The Mo-C(cyclobutadienyl) bond lengths [2.189 (2)-2.211 (2) A] are unusually short, probably reflecting strong electron withdrawal by the trifluoromethyl groups. The molecules straddle crystallographic mirror planes.

The low-temperature phase transition of 9-methylfluoren-9-ol: comparison of the crystal structures at 100 and 200 K.

Crystals of 9-methylfluoren-9-ol, C(14)H(12)O, undergo a reversible phase transition at 176 (2) K. The structure of the high-temperature alpha form at 200 K is compared with that of the low-temperature beta form at 100 K. Both polymorphs crystallize in space group P1 with Z = 4 and contain discrete hydrogen-bonded R(4)(4)(8) ring tetramers arranged around crystallographic inversion centres. The most obvious changes observed on cooling the crystals to below 176 K are an abrupt increase of ca 0.5 A in the shortest lattice translation, and a thermal transition with deltaH = 1 kJ mol(-1).

Tetrameric dichloro(trimethylammonio-p-toluenesulfonamidate)mercury(II).

In the title compound, hexa-micro-chloro-dichlorotetrakis(N-trimethylammonio-p-toluenesulfonamidate-kappa(2)N,O)tetramercury(II), [Hg[Me(3)N(+)N(-)SO(2)C(6)H(4)CH(3)-p]Cl(2)](4) or [Hg(4)Cl(8)(C(10)H(16)N(2)O(2)S)(4)], four nearly linear and parallel Cl-Hg-Cl units associate through pairwise Hg.Cl interactions of 3.1-3.2 A. Each Hg atom is also coordinated through N and O atoms to a ylide molecule. The available structural data indicate that coordination of a sulfonyl-stabilized nitrogen ylide to a metal atom (Hg or Ag) has no detectable effect on its geometry.

4-Chloro-N-(trimethylammonio)benzamide chloride monohydrate.

The structure of the cation in the ylide hydrochloride [Me(3)NNHC(O)C(6)H(4)-Cl-p]Cl.H(2)O, or C(10)H(14)ClN(2)O(+).Cl(-).H(2)O, is compared with that of the free ylide. Protonation lengthens the N-C(O) bond but shortens the C=O and N-N bonds by approximately 0.03 A and increases the dihedral angle between the phenyl and ylide planes.

Sodium 1-carboxycyclopropane-1-carboxylate cyclopropane-1,1-dicarboxylic acid monohydrate.

In the title type B(2) acid salt, Na(LH)(LH(2)).H(2)O [LH(2) = C(2)H(4)C(CO(2)H)(2)] or Na(+).C(5)H(5)O(4)(-).C(5)H(6)O(4).H(2)O, the vertices of a distorted octahedron centred on each Na(+) cation are defined by six O atoms, one from a water molecule, one from an internally hydrogen-bonded LH(-) anion and four from three neutral LH(2) acid molecules. Chains of edge-sharing O(6) octahedra are stabilized by hydrogen bonds, which interconnect the donor H(2)O and LH(2) molecules and LH(-) anions. In particular, the LH(2) molecule donates H atoms to LH(-) and H(2)O and forgoes the internal hydrogen bond which stabilizes the free acid and all of its characterized salts.

The remarkable effect of cosolvent on a samarium(II)-mediated 4-exo-trig cyclization: further synthetic studies on pestalotiopsin A.

A samarium(II)-mediated 4-exo-trig cyclization in which a remote stereocenter serves to control the facial selectivity of the cyclization is described. The apparent coordination of a tert-butyldimethylsilyl ether to the samarium center appears to give rise to the selectivity. The remarkable effect of the cosolvent, 2,2,2-trifluoroethanol, on the cyclization of this substrate, is also discussed. A stereoselective synthesis of the general class of gamma,delta-unsaturated aldehyde cyclization substrate is reported, and the utility of the cyclization is demonstrated in an approach to the fully functionalized core of pestalotiopsin A.

(2RS)-5,6:7,8-Dibenzobicyclo[2.2.2]octan-2-ol.

The racemic form of the title secondary monoalcohol, C(16)H(14)O, forms crystals in which the molecules are linked into chains by hydrogen bonding. The chain architecture is unusual; adjacent molecules are related pseudosymmetrically, by either a pseudo-diad or a pseudo-glide plane, while alternate molecules are related exactly by a crystallographic glide plane.

The first synthetic studies on pestalotiopsin A. A stereocontrolled approach to the functionalised bicyclic core.

Pestalotiopsin A is a structurally unique, caryophyllene-type sesquiterpene which has shown immunosuppressive activity and cytotoxicity in preliminary assays. A stereocontrolled approach to the functionalised 2-oxabicyclo[3.2.0]-heptane core of pestalotiopsin A is described. This constitutes the first synthetic studies on pestalotiopsin A. Our approach includes a samarium(II)-mediated 4-exo-trig cyclisation and a trans-lactonisation process triggered by the addition of alkylytterbium reagents to a cyclobutanone intermediate. Further manipulation provides access to advanced intermediates which are excellent precursors for the future construction of the final ring of the target.

Reaction of BH4- with [Mo2Cp2(mu-SMe)n] species to give tetrahydroborato, hydrido or dimetallaborane compounds: control of product by ancillary ligands.

The reaction of mono- or dichloro-dimolybdenum(III) complexes [Mo2Cp2(mu-SMe)2(mu-Cl)(mu-Y)] (Cp=eta5-C5H5; 1, Y=SMe; 2, Y=PPh2; 3, Y=Cl) with NaBH4 at room temperature gave in high yields tetrahydroborato (8), hydrido (9) or metallaborane (12) complexes depending on the ancillary ligands. The correct formulation of derivatives and has been unambigously determined by X-ray diffraction methods. That of the hydrido compound 9 has been established in solution by NMR analysis and confirmed by an X-ray study of the mu-azavinylidene derivative [Mo2Cp2(mu-SMe)2(mu-PPh2)(mu-N=CHMe)] (10) obtained from the insertion of acetonitrile into the Mo-H bond of 9. Reaction of NaBH4 with nitrile derivatives, [Mo2Cp2(mu-SMe)4-n(CH3CN)2n]n+(5, n=1; 6 n=2), afforded the tetrahydroborato compound 8, together with a mu-azavinylidene species [Mo2Cp2(mu-SMe)3(mu-N=CHMe)](14), when n=1, and the metallaborane complex 12, together with a mixed borohydrato-azavinylidene derivative [Mo2Cp2(mu-SMe)2(mu-BH4)(mu-N=CHMe)] (13), when n=2. The molecular structures of these complexes have been confirmed by X-ray analysis. Preparations of some of the starting complexes (3 and 4) are also described, as are the molecular structures of the precursors [Mo2Cp2(mu-SMe)2(mu-X)(mu-Y)] (1, X/Y=Cl/SMe; 2, X/Y=Cl/PPh2; 4, X/Y=SMe/PPh2).

Self-assembly of polymer and sheet structures in palladium(II) complexes containing carboxylic acid substituents.

A series of complexes trans-[PdCl(2)L(2)] has been prepared by the reaction of [PdCl(2)(PhCN)(2)] and/or Na(2)[PdCl(4)] with L = pyridine or quinoline ligands having one or two carboxylic acid groups. These complexes can form 1-D polymers through O-H.O hydrogen bonding between the carboxylic acid groups, as demonstrated by structure determinations of [PdCl(2)(NC(5)H(4)-4-COOH)(2)], [PdCl(2)(NC(5)H(4)-3-COOH)(2)], and [PdCl(2)(2-Ph-NC(9)H(5)-4-COOH)(2)]. In some cases, solvation breaks down the O-H.O hydrogen-bonded structures, as in the structures of [PdCl(2)(NC(5)H(4)-3-COOH)(2)].2DMSO and [PdCl(2)(2-Ph-NC(9)H(5)-4-COOH)(2)].4DMF, while pyridine-2-carboxylic acid underwent deprotonation to give the chelate complex [Pd(NC(5)H(4)-2-C(O)O)(2)]. The complexes trans-[PdCl(2)L(2)], L = pyridine-3,5-dicarboxylic acid or 2,6-dimethyl pyridine-3,5-dicarboxylic acid, self-assembled to give 2-D sheet structures, with hydrogen bonding between the carboxylic acid groups mediated by solvate methanol or water molecules. In the cationic complexes [PdL'(2)L(2)](2+) (L'(2) = Ph(2)PCH(2)PPh(2), Ph(2)P(CH(2))(3)PPh(2); L = pyridine carboxylic acid; anions X(-) = CF(3)SO(3)(-)), hydrogen bonding between the carboxylic acid groups and anions or solvate acetone molecules occurred, and only in one case was a polymeric complex formed by self-assembly.

1,1-bis(phenylsulfonyl)-1-(pyridinio)methanide.

The title disulfonyl-stabilized pyridinium ylide, C(5)H(5)N(+)-C(-)(SO(2)C(6)H(5))(2) or C(18)H(15)NO(4)S(2), contains a near planar NCS(2) core. The structure suggests that the formal negative charge of the ylide C atom is delocalized to the S atoms rather than the N atom. Structural features of pyridinium ylides are briefly discussed.

Electrochemical cleavage of N=N bonds at a Mo2(mu-SMe)3 site relevant to the biological reduction of dinitrogen at a bimetallic sulfur centre.

The reduction of diazene complexes [Mo(2)Cp(2)(mu-SMe)(3)(mu-eta(2)-H-N=N-R)](+) (R=Ph (3 a); Me (3 b)) and of the hydrazido(2-) derivative [Mo(2)Cp(2)(mu-SMe)(3)[mu-eta(1)-N=N(Me)H]](+) (1 b) has been studied by cyclic voltammetry, controlled-potential electrolysis, and coulometry in THF. The electrochemical reduction of 3 a in the presence of acid leads to cleavage of the N=N bond and produces aniline and either the amido complex [Mo(2)Cp(2)(mu-SMe)(3)(mu-NH(2))] 4 or the ammine complex [Mo(2)Cp(2)(mu-SMe)(3)(NH(3))(X)] 5, depending on the initial concentration of acid (HX=HTsO or CF(3)CO(2)H). The N=N bond of the methyldiazene analogue 3 b is not cleaved under the same conditions. The ability of 3 a but not 3 b to undergo reductive cleavage of the N=N bond is attributed to electronic control of the strength of the Mo-N(R) bond by the R group. The electrochemical reduction of the methylhydrazido(2-) compound 1 b in the presence of HX also results in cleavage of the N=N bond, with formation of methylamine, 4 (or 5) and the methyldiazenido complex [Mo(2)Cp(2)(mu-SMe)(3)(mu-eta(1)-N=N-Me)]. Formation of the last of these complexes indicates that two mechanisms (N=N bond cleavage and possibly H(2) production) are operative. A pathway for the reduction of N(2) at a dinuclear site of FeMoco is proposed on the basis of these results.

Di-iron aza diphosphido complexes: mimics for the active site of Fe-only hydrogenase, and effects of changing the coordinating atoms of the bridging ligand in [Fe2[mu-(ECH2)2NR](CO)6].

The bis(phosphido)-bridged complex [Fe(2)(mu-PPhH)(2)(CO)(6)] (1) undergoes double deprotonation to give the phosphorus-centered dianionic derivative [Fe(2)(mu-PPh)(2)(CO)(6)](2)(-) (2) which in turn reacts with the tertiary base RN(CH(2)Cl)(2) to give [Fe(2)[(PPhCH(2))(2)NR](CO)(6)] (3) in moderate yield. Treatment of 3 with HBF(4).Et(2)O affords the N-protonated species [Fe(2)[(PPhCH(2))(2)NHR](CO)(6)] BF(4) (4). The structural changes to the heavy atom skeleton of 3 arising from protonation are slight, the most obvious being a ca. 0.03 Alengthening of the N-C bonds.

Self-recognition and hydrogen bonding by polycyclic bridgehead monoalcohols.

Our interest in the relationship between the hydrogen bonding motifs displayed by monoalcohols and the properties of the solids which contain these motifs has led us to determine the crystal structures of three polycyclic bridgehead monoalcohols. One C10H16O isomer crystallises in the space group P2(1)2(1)2(1) but the three molecules which comprise the asymmetric unit are related approximately by the operations of a 3(1) screw axis. They are linked by hydrogen bonds to form an infinite helix. A second C10H16O isomer forms rings containing four molecules joined by cooperative hydrogen bonds. The chiral space group P4(1)2(1)2 accommodates molecules of the S,S and R,R enantiomers in the molar ratio 92:8 (ee 84%) owing to disorder. A related C9H14O2 keto-alcohol forms infinite chains by C-OH...O = C hydrogen bonding. These hydrogen bond motifs are shown to be typical for 45 tertiary monoalcohols, CmHnOH, present in the Cambridge Structural Database. Tertiary monoalcohols display in a more pronounced form the strong preferences for trigonal and tetragonal space groups and for asymmetric units containing several molecules which are established features of the crystallochemistry of monoalcohols.