The molecular structure and conformational composition of epichlorohydrin as determined by gas phase electron diffraction

The molecular structure of gaseous epichlorohydrin has been investigated using electron diffraction data obtained at 67°C. The conformational composition at this temperature is such that the molecules exist predominantly in a gauche-2 conformer (where the C---Cl bond is 160° away from the C---O) bond). Refinements showed that 33% (σ = 4) of the molecule exist in the gauche-1 form. The important distances (r_g) and angle () with the associated uncertainties are r(C---H) = 1.095(5) Å, r(C---O) = 1.442(3) Å, r(C---C) = 1.475(8) Å, r(C---C_M) = 1.523(7) Å, r(C---Cl) = 1.788(2) Å, CCO = 114° (1), CCC_M = 119°(1), ClCC = 108.9° (7), and Tau(ClCCO) = −150°(10) (gauche-2) and Tau(ClCCO) = 78° (10) (gauche-1).     

Calorimetric study of the relationship between molecular structure and liquid-crystallinity of rod-like mesogens I. Heat capacities and phase transitions of 4'-propylbiphenyl-4-carbonitrile and trans, trans-4'-propylbicyclohexyl-4-carbonitrile

The heat capacities of the rod-like compounds 4'-propylbiphenyl-4-carbonitrile (3-BBCN) and trans, trans-4'-propylbicyclohexyl-4-carbonitrile (3-CCCN) have been measured with an adiabatic calorimeter between 12 and 383 K. 3-BBCN is not mesogenic and melts into an isotropic liquid at 338·77 K, whereas 3-CCCN is mesogenic and its melting and clearing points are 330·73 K and 353·80 K, respectively. The enthalpy and entropy of fusion of 3-BBCN are 22·7 kJ mol^-1 and 67·0 J K^-1 mol^-1, respectively, while those of 3-CCCN are 27·0 kJ mol^-1 and 81·7 J K^-1 mol^-1, respectively. The enthalpy and entropy gain due to the nematicisotropic transition of 3-CCCN are 1·8 kJ mol^-1 and 5·0 J K^-1 mol^-1. 3-CCCN shows a mesomorphic transition from a smectic to the nematic state at 329·62 K, which occurs as a metastable state, its transition enthalpy and entropy are 5·4 kJ mol^-1 and 16·4 J K^-1 mol^-1, respectively. The temperature dependence of the molar entropies of both compounds shows that molecular arrangement in the crystal is more ordered in 3-CCCN than in 3-BBCN. This fact may be related to the stability of mesophases. Finally, Eidenschink's theoretical model for the nematicisotropic transition has been applied to 3-CCCN. As far as the present mesogen is concerned, the transition enthalpy estimated according to this model agrees well with the observed value.     

Structural and spectral studies of N-2-(pyridyl)-, N-2-(3-, 4-, 5-, and 6-picolyl)- and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenylthioureas

Structures of the following compounds have been obtained: N-(2-pyridyl)-N′-2-thiomethoxyphenylthiourea, PyTu2SMe, monoclinic, P2₁/c, a=11.905(3), b=4.7660(8), c=23,532(6) Å, β=95.993(8)°, V=1327.9(5) ų and Z=4; N-2-(3-picolyl)-N′-2-thiomethoxyphenyl-thiourea, 3PicTu2SeMe, monoclinic, C2/c, a=22.870(5), b=7.564(1), c=16.941(4) Å, β=98.300(6)°, V=2899.9(9) ų and Z=8; N-2-(4-picolyl)-N′-2-thiomethoxyphenylthiourea, 4PicTu2SMe, monoclinic P2₁/a, a=9.44(5), b=18.18(7), c=8.376(12) Å, β=91.62(5)°, V=1437(1) ų and Z=4; N-2-(5-picolyl)-N′-2-thiomethoxyphenylthiourea, 5PicTu2SMe, monoclinic, C2/c, a=21.807(2), b=7.5940(9), c=17.500(2) Å, β=93.267(6)°, V=2893.3(5) ų and Z=8; N-2-(6-picolyl)-N′-2-thiomethoxyphenylthiourea, 6PicTu2SMe, monoclinic, P2₁/c, a=8.499(4), b=7.819(2), c=22.291(8) Å, β=90.73(3)°, V=1481.2(9) ų and Z=4 and N-2-(4,6-lutidyl)-N′-2-thiomethoxyphenyl-thiourea, 4,6LutTu2SMe, monoclinic, P2₁/c, a=11.621(1), b=9.324(1), c=14.604(1) Å, β=96.378(4)°, V=1572.4(2) ų and Z=4. Comparisons with other N-2-pyridyl-N′-arylthioureas having substituents in the 2-position of the aryl ring are included.     

Synthesis and crystal structure of 9,10-dihydro-9,10-etheno-1,8-dichloro-11-diphenylphosphinyl-12-(diphenylphosphinylethynyl)anthracene

The title compound, 9,10-dihydro-9,10-etheno-1,8-dichloro-11-diphenylphosphinyl-12-(diphenylphosphinylethynyl)anthracene (1), has been synthesized and its crystal structure has been determined. The compound 1 crystallized into the triclinic space group P-1 with =74.837(4)°, β=88.156(4)°, γ=65.398(4)°, Z=2, D_c=1.352 gcm⁻³. In the crystal structure of 1a, one chloroform molecule was included by the compound 1 with a 1:1 ratio and the existence of non-classical intermolecular C–HO hydrogen bonds, intramolecular C–HCl and C–HO hydrogen bonds and π–π stacking were observed.     

Spectrophotometric determination of ruthenium with 8-quinolinol

A spectrophotometric method is described for the determination of 2–80 μg of ruthenium. The method involves oxidation of ruthenium to ruthenate, addition of 8-quinolinol, adjustment of the pH to 4–6.5, digestion of the complex formed at 85° for 30 min, extraction with chloroform, and measurement of absorbance at 430 nm. Almost all other metals and excess of reagent are removed by washing the extract. About 98 % of ¹⁰⁶Ru tracer was recovered.     

The conformations of 1,2-acenaphthene derivatives and steric interaction of contiguous nitroxy groups

Inter-oxygen distances and conformational flexibility were estimated for cis- and trans-1,2-acenaphthenediol from X-ray data, intramolecular hydrogen bonding, the kinetics of glycol cleavage, and cyclization experiments. The optical and NMR spectra of the isomeric dinitrate esters and related compounds in solution showed significant differences. The symmetric and anti-symmetric stretching bands of the nitroxy group occurred at 1276 ± 2 cm⁻¹ and 1639 ± 7 cm⁻¹ respectively in the trans-dinitrate and in ethyl and benzyl nitrates and were shifted to higher frequencies by 9 cm⁻¹ and 16 cm⁻¹ respectively in the cis-dinitrate. The analogy to similar effects observed in cyclic 1,2-diketones, -haloketones, and o-halonitrobenzenes suggested intramolecular interaction of the contiguous nitroxy groups.

The reaction of the dinitrates with pyridine at 25° was pseudo first-order and the ratio k_trans/k_cis of 6·5 was consistent with an E_CO mechanism involving nitroxy group interaction in the cis isomer.     

Synthesis and crystal structure of two novel nickel (imidazole) complexes having hydrogen-bonded networks

Two nickel (imidazole) complexes, Ni(im)₆Cl₂·4H₂O (1) and Ni(im)₆(NO₃)₂ (2) (im=imidazole) have been synthesized and characterized by elemental analysis, IR, UV, TG and single crystal X-ray diffraction. 1 crystallizes in the triclinic space group P-1 with a=8.800(6) Å, b=9.081(6) Å, c=10.565(7) Å, =75.058(9)°, β=83.143(8)°, γ=61.722(8)°, V=718.3(8) Å³, Z=1 and R₁ (wR₂)=0.0469 (0.1497). 2 crystallizes in the trigonal space group R-3 with a=12.370(6) Å, b=12.370(6) Å, c=14.782(14) Å, =90.00°, β=90.00°, γ=120.00°, V=1959(2) Å³, Z=3 and R₁ (wR₂)=0.0358 (0.0955). 1 and 2 exhibit different supramolecular network due to their different counter anions and different hydrogen bonding connection. In compound 1, [Ni(im)₆]²⁺ cation and counter anions Cl⁻ alternatively array in an ABAB fashion via N–HCl hydrogen bonding. In compound 2, the plane of each NO₃²⁻ is almost parallel and each NO₃²⁻ connect three different [Ni(im)₆]²⁺ cations via N–HO hydrogen bonding.     

Synthesis and X-ray crystal structures of rac- and meso-2,2′-propylidene-bis(1-indenyl) zirconium dichlorides

An improved synthesis of 2,2′-bis(1-indenyl)propane and the corresponding ansa-complexes of zirconium are reported. Synthesis of a mixture of rac- and meso-2,2′-propylidene-bis(1-indenyl)zirconium dichlorides involves a treatment of ZrCl₄ with bis[3-(trialkyltin)inden-1-yl]propane, where alkyl = ethyl, butyl, in toluene. This reaction gives the products in 92% yield and might be a convenient synthetic pathway to a number of straightforward ansa-metallocenes. Both rac- and meso-2,2′-propylidene-bis(1-indenyl)zirconium dichlorides were separated and isolated using simple work-up processes, and characterized by X-ray crystal structure analysis (rac:C2/c; a = 15.903(3) Å, b = 11.105(2) Å and c = 11.520(2) Å; β = 121.61(3)°; Z = 4; V = 1732.6(5) ų; R = 0.0350; meso-: P1¯; a = 9.739(2) Å, b = 12.798(4) Å and c = 15.322(4) Å; = 101.18(2)°; β = 121.61(2)°; γ = 90.54(2)°, Z = 4; V = 1795.4(8) ų; R = 0.0417).     

Steric effects in the complexation kinetics of copper(II) with rac-5,5,7,12,12,14-hexamethyl 1,4,8,11-tetraazacyclotetradecane in basic aqueous media

Copper(II) reacts with rac-5,5,7,12,12,14-hexamethyl-l,4,8,11-tetraazacyclotetradecane (tet-b) in strongly basic aqueous media to give [Cu(tet-b) (OH) (blue)]⁺ which contains trigonal bipyramidally co-ordinated Cu²⁺ with the tet-b ligand in its most stable, folded form. The kinetics of formation of this blue complex have been studied at 25.0° ± 0.1°C using the stopped-flow technique. Second-bond formation is proposed as the rate-determining step for tet-b reaction with Cu(OH)^-₃ and Cu(OH)^2-₄. Possible mechanisms for the reaction and the steric effects resulting from the methyl groups on the alkyl backbone of the macrocyclic ligand are considered.     

N, C and Sn NMR and other spectroscopic studies of 8-quinolinol, its O- and N-methyl derivatives, and chelate di- and tri-organotin(IV) complexes

The nature of the 8-quinolinato ligand in various forms has been examined by ¹⁵N, ¹³C and ¹¹⁹Sn NMR spectroscopy, with evidence also from electronic spectroscopy. These forms include 8-quinolinol (HQ), 8-quinolinate, the 8-hydroxyquinolinium ion, O- and N-methyl derivatives, 8-methoxyquinoline (MeQ), the zwitterionic N-methylquinolinium-8-olate and the N-methylquinolinium ion, and the chelating ligand in organotin(IV) complexes. The ¹⁵N shift from MeQ to HQ affords a measure of the intramolecular hydrogen bonding in HQ. The ¹⁵N shifts and ²J(¹⁵N¹H) couplings afford criteria of chelation, and the O- and N-methyl compounds provide useful reference points for its assessment. Evidence for chelation is demonstrated in three groups of compounds, [SnR₂Q₂] (R = Me, Et, Buⁿ, Octⁿ or Ph), [SnR₃Q] (R = Me, Et, Buⁿ or Ph) and [SnR₂ClQ] (R = Me, Et, Buⁿ or Octⁿ), the ¹⁵N and ¹¹⁹Sn shielding increasing from the [SnR₃Q] to the [SnR₂Q₂] compounds.     

Structure and conformation of 2,3,4-triphenyl-1-oxa-4-azabutadiene

2,3,4-triphenyl-1-oxa-4-azabutadine (C20H15NO) has been studied by X-ray analysis and AM1 molecular orbital methods. It crystallises in the triclinic space group P-1 with a=9.414(3), b=10.479(3), c=8.385(2) Å, =103.31(3)°, β=97.10(3)°, γ=74.09(1)°, V=772.5(4) ų, Z=2, D_c=1.227 gcm⁻³, and μ(MoK)=0.075 mm⁻¹ and F₀₀₀=300. The structure was solved by direct methods and refined to R=0.043 for 2672 reflections [I>2σ(I)]. The conformational analysis of the title compound were investigated by semi-empirical quantum mechanical AM1 calculations. The minimum conformation energies were calculated as a function of the three torsion angles θ₁(O(1)C(7)C(8)N(1)), θ₂(C(8)N(1)C(15)C(16)) and θ₃(C(14)C(9)C(8)N(1)). The results are compared with the X-ray results. C=O and C=N groups are twisted about each other by 95.5(2)°.     

Misenine,a Novel Macrocyclic Alkaloid with an Unusual Skeleton from the Mediterranean Sponge Reniera sp

PolycycJic marine alkaloids containing 3-alkylpyridine or partially reduced 3-alkylpyridine as basic building blocks represent an emerging and intriguing group of bioactive natural products from marine sponges. Since halitoxin,² the first example of this kind of alkaloid, was reported in 1978, many related alkaloids have been discovered from sponges of the order Haplosclerida. All of these alkaloids, in spite of formally exhibiting quite different frameworks, could biogeneticaliy derive from bis-3-alkylpyridine or reduced bis-3-alkylpyridine units. In the last decade, the knowledge of this fascinating group of compounds has increased remarkably. A recent review has exhaustively studied occurrence, distribution, plausible biogenetic origin and relatedness, as well as biological activities, of 3-alkylpyridine derived marine alkaloids.³     

The ion-pair association constant of oxalate with fac-tris(2-aminomethylpyridine)cobalt(III)

The equilibrium constant K for the ion-pair formation fac-[Co(pic)₃]³⁺ + C₂O₂₂₋ fac-[Co(pic)₃]³⁺/C₂O₄²⁻¹ where pic = 2-aminomethylpyridine, has been determined spectrophotometrically at 0.35 M (KCl) ionic strength and 25.0°C, using four different calculation approaches. The best results were obtained when the concentration of the minor component (the cobalt complex ion) was not neglected in comparison with the oxalate ion concentration. The value of K (5.3 M⁻¹) increases when the supporting electrolyte is LiCl (K = 8.2 M⁻¹). The effect of the ionic strength variation from 0.35 to 2.0 M (LiCl) was also investigated.     

E-(hydroxyimino)(hydroxymethoxyphosphinyl)acetic acid: Synthesis and pH-dependent fragmentation

In contrast to both its parent “troika” acid (E-1, a phosphorylating agent at pH 7 and 25 °C) and its C-methyl isomer (E-2, which is stable at both acidic and neutral pH), (E)-(hydroxyimino)(hydroxymethoxyphosphinyl)acetic acid E-3 was unreactive at pH 7 and 25 °C but at pH 1.5 fragmented to methyl phosphate 10 (15%) and methyl phosphorocyanidate 11 (85%). The minor product is consistent with solvent phosphorylalion, the reaction exclusively observed with E-1. The non-phosphorylating fragmentation pathway is proposed to involve a preliminary E→ Z isomerizalion of 3 prior to C-C_β cleavage. Dual fragmentation pathways were also detected (³¹P NMR) when the DCHA⁺ salt of E-3 (E-9) was heated in acetonitrile or EtOH; in addition to phosphorylation products (16–19%), 11 was formed (81–84%). Reaction of E-9 in refluxing EtOH:t-BuOH (1:1) showed low stereoselectivity in product formation (~3:1 ethyl methyl phosphate:t-butyl methyl phosphate), supporting a dissociative phosphorylation process.     

Diastereoselective synthesis of a resolved secondary arsine complex: asymmetric synthesis of (R-(−)589-ethylmethylphenylarsine

The reaction of [R-(R,R)]-(+)₅₈₉-[(η⁵-C₅H₅){1,2-C₆H₄(PMePh)₂}Fe(NCMe)]PF₆ with (±)-AsHMePh in boiling methanol yields crystalline [R-[(R)-(R,R)]-(+)_{589)-[(η⁵-C5H5){1,2-C6H4(PMePh)2}Fe(AsHMePH)}PF₆, optically pure, in ca. 90% yield, in a typical second-order asymmetric transformation. This complex contains the first resolved secondary arsine. Deprotonation of the secondary arsine complex with KOBu^t at −65°C gives the diastereomerically pure tertiary arsenido-iron complex [R-[(R),(R,R)]]-[((η⁵-C₅H₅){1,2-C₆H₄(PMePh)₂}FeAsMePh] · thf, from which optically pure [R-[(S),(R,R)]]-(+)₅₈₉-[(η⁵-C₅H₅){1,2-C₆H₄(PMePh)₂}Fe(AsEtMePh)PF₆ is obtained by reaction with iodoethane. Cyanide displaces (R)-(−)₅₈₉-ethylmethylphenylarsine from the iron complex, thereby effecting the asymmetric synthesis of a tertiary arsine, chiral at arsenic, from (±)-methylphenylarsine and an optically active transition metal auxiliary.     

Syntheses, crystal structures and electronic properties of a series of copper(II) complexes with 3,5-halogen-substituted Schiff base ligands and their solutions

We have systematically investigated the structural features, electronic properties, thermally-induced structural phase transitions and absorption spectra depending on the solvent for ten Cu(II) complexes with 3,5-halogen-substituted Schiff base ligands. Structural characterization of two new complexes, bis(N-R-1-phenylethyl- and N-R,S-2-butyl-5-bromosalicydenaminato-κ²N,O)copper(II), reveals that they afford a compressed tetrahedral trans-[CuN₂O₂] coordination geometry with trans-N–Cu–N = 159.4(2)° and trans-O–Cu–O = 151.7(3)° for the 1-phenylethyl complex and trans-N–Cu–N = 157.9(3)° and trans-O–Cu–O = 151.0(3)° for the 2-butyl one. All the complexes exhibit a structural phase transition by heating in the solid state regardless of their structures at room temperature. The absorption spectra of a series of ten complexes exhibit a slight shift of the d–d band at 16 000–20 000 cm⁻¹ and remarkable shift of the π–π* band at 24 000–28 000 cm⁻¹, which suggests that the dipole moment of the solvents presumably affects the conformation of the π-conjugated moieties of the ligands rather than the coordination environment. We have also attempted ‘photochromic solute-induced solvatochromism’ by a system of bis(N-R-1-phenylethyl-3,5-dichlorosalicydenaminato-κ²N,O)copper(II) and photochromic 4-hydroxyazobenzene in chloroform solution. We successfully observed a change of the d–d and π–π* bands of the complex in the absorption spectra caused by cis–trans photoisomerization of 4-hydroxyazobenzene.     

Reactive intermediates in asymmetric cross-coupling catalysed by palladium P-N chelates

The palladium dibromide complexes of (S,R)-(1,1′-bis-diphenylphosphino)-2-ferrocencylthyldimethylamine and (S,R)-(1-diphenylphosphino)-2-ferrocenylethyldimethylamine have been reduced with dilithiocyclooctatetraene to form the corresponding Pd⁰ cyclooctatetraene complexes. Their reactions with E-4-methoxy-2′-bromophenylethene, and then benzylmagnesium chloride at −60 to −30°C, provide information on the structure of intermediates in asymmetric cross-coupling.     

Structural, spectral and thermal studies of N-2-(4-picolyl)- and N-2-(6-picolyl)-N′-(2-chlorophenyl)thioureas and N-2-(6-picolyl)-N′-(2-bromophenyl)thiourea

N-2-(4-picolyl)-N′-2-chlorophenylthiourea, 4PicTu2Cl, monoclinic, P2₁/c, a=10.068(5), b=11.715(2), β=96.88(4)°, and Z=4; N-2-(6-picolyl)-N′-2-chlorophenylthiourea, 6PicTu2Cl, triclinic, P-1, a=7.4250(8), b=7.5690(16), c=12.664(3) Å, =105.706(17), β=103.181(13), γ=90.063(13)°, V=665.6(2) ų and Z=2 and N-2-(6-picolyl)-N′-2-bromophenylthiourea, 6PicTu2Br, triclinic, P-1, a=7.512(4), b=7.535(6), c=12.575(4) Å, a=103.14(3), β=105.67(3), γ=90.28(4)°, V=665.7(2) ų and Z=2. The intramolecular hydrogen bonding between N′H and the pyridine nitrogen and intermolecular hydrogen bonding involving the thione sulfur and the NH hydrogen, as well as the planarity of the molecules, are affected by the position of the methyl substituent on the pyridine ring. The enthalpies of fusion and melting points of these thioureas are also affected. ¹H NMR studies in CDCl₃ show the NH′ hydrogen resonance considerably downfield from other resonances in their spectra.     

Nido-6-metalladecaborane chemistry: Molecular structure and fluxionality of [6,6,6,6-(CO)2(PPh3)2-nido-6-WB9H13]

The molecular and crystal structure of the nido-6-tungstadecaborane [6,6,6,6-(CO)₂(PPh₃)₂-nido-6-WB₉H₁₃] (1) has been determined showing that the tungsten atom is incorporated into the 6-position of a nido 10-vertex (WB₉) cage. The tungsten atom has a seven-coordinate capped trigonal prismatic environment and is bonded to two hydrogen and three boron atoms of the {B₉H₁₃} cage, in addition to two CO groups and two PPh₃ ligands. Variable-temperature (−90°C to +50°C) ³¹P{¹H} NMR spectroscopy of 1 reveals that the exo-polyhedral ligands about the tungsten atom are fluxional with respect to PPh₃ site exchange with an activation energy (ΔG‡), at the coalescence temperature (−73°C), of <38 kJ mol⁻¹.     

Synthesis and characterization of planarly chiral nonbridged bis(1-R-indenyl) zirconium dichloride complexes and X-ray structure of rac-[(η-C9H6-1-C(CH3)2---o-C6H4---OCH3)2ZrCl2]·THF

Reactions of the lithium salts of 3-substituted indenes 1, 2 with ZrCl₄(THF)₂ gave two series of nonbridged bis(1-substituted)indenyl zirconocene dichloride complexes. Fractional recrystallization from THF–petroleum ether furnished the pure racemic and mesomeric isomers of [(η⁵-C₉H₆-1-C(R¹)(R²)---o-C₆H₄---OCH₃)₂ZrCl₂]·nTHF (R¹=R²=CH₃, n=1, rac-1a and meso-1b; R¹=CH₃, R²=C₂H₅; n=0.5 or 0, rac-2a and meso-2b), respectively. Complex 1a was further characterized by X-ray diffraction to have a C₂ symmetrically racemic structure, where the six-member rings of the indenyl parts are oriented laterally and two o-CH₃O---C₆H₄---C(CH₃)₂--- substituents are oriented to the open side of the metallocene (Ind: bis-lateral, anti; Substituent: bis-central, syn). The four zirconocene complexes are highly symmetrical in solution as characterized by room temperature ¹H-NMR, however ¹H–¹H NOESY of meso-1b shows that some of the NOE interactions arise from the two separated indenyl parts of the same molecule, which can only be well explained by taking into account the torsion isomers in solution.