Crystal structure of 2,4-di-nitro-phenyl 4-methyl-benzene-sulfonate: a new polymorph

The title compound, C13H10N2O7S, was synthesized via a nucleophilic substitution reaction between 2,4-di-nitro-phenol and p-toluene-sulfonyl chloride. This crystal structure is a polymorph of CSD entry WUVYUH [Vembu et al. (2003). Acta Cryst, E59, o378-380]. The aromatic substituents on the sulfonate group are oriented gauche to one another with a C-O-S-C torsion angle of -62.0 (3)°. The supra-molecular features that contribute to the crystal stability are offset π-π [centroid-centroid distance = 3.729 (2) Å] and multiple C-H⋯O inter-actions.

Crystal structure of 3,5-di-methyl-phenyl 2-nitro-benzene-sulfonate

The title compound, C14H13NO5S, was synthesized via a nucleophilic substitution reaction between 3,5-di-methyl-phenol and 2-nitro-benzene-sulfonyl chloride. The aromatic rings attached to the SO3 group are oriented in a gauche fashion around the ester S-O bond, with a C-S-O-C torsion angle of 84.68 (11)°. The mol-ecules form centrosymmetric dimers via π-π stacking inter-actions between 3,5-di-methyl-phenyl groups (centroid-centroid distance = 3.709 Å). An inter-molecular S=O⋯N inter-action between the sulfonyl and nitro groups, with an O⋯N distance of 2.9840 (18) Å, organizes the dimers into columns extending along [011]. These columns are further assembled into (111) layers through C-H⋯O inter-actions.

Highly Stereoselective Intermolecular Haloetherification and Haloesterification of Allyl Amides

An organocatalytic and highly regio-, diastereo-, and enantioselective intermolecular haloetherification and haloesterification reaction of allyl amides is reported. A variety of alkene substituents and substitution patterns are compatible with this chemistry. Notably, electronically unbiased alkene substrates exhibit exquisite regio- and diastereoselectivity for the title transformation. We also demonstrate that the same catalytic system can be used in both chlorination and bromination reactions of allyl amides with a variety of nucleophiles with little or no modification.

Crystal structure of bis-(3,3-dimethyl-2-oxobut-yl)di-phenyl-phospho-nium bromide chloro-form monosolvate

In the title salt solvate, C24H32O2P(+)·Br(-)·CHCl3, the P atom has a distorted tetra-hedral geometry, and the planes of the phenyl rings form a dihedral angle of 71.86 (14)° with one another. The bromide anion is disordered and was modelled over three positions (occupancy ratio 0.50:0.35:0.15). The crystal also contains one disordered chloro-form solvent mol-ecule that was modeled over three positions (occupancy ratio 0.50:0.35:0.15). Weak inter-molecular inter-actions (C-H⋯Br and C-H⋯O) exist between the complex cation and the bromide anion fragments. The resulting supramolecular structure is an oval-shaped arrangement of phosphonium salt molecules that surround the disordered bromide anion.

Crystal structures of 1-(4-chloro-phen-yl)-2-(di-phenyl-phosphor-yl)ethan-1-one and 1-(di-phenyl-phosphor-yl)-3,3-di-methyl-butan-2-one

The title compounds were synthesized via an Arbuzov reaction between an α-bromo­ketone and isopropoxydi­phenyl­phosphane. In the crystals of both compounds, mol­ecules are linked via bifurcated C—H⋯(O,O) hydrogen bonds, forming chains propagating along [100] and along [010].

The title compounds, C₂₀H₁₆ClO₂P, (I), and C₁₈H₂₁O₂P, (II), were synthesized via an Arbuzov reaction between an α-bromo­ketone and isopropoxydi­phenyl­phosphane. In the crystals of both compounds, mol­ecules are linked via bifurcated C—H⋯(O,O) hydrogen bonds, forming chains propagating along [100] for (I) and along [010] for (II). The chains are linked via C—H⋯π inter­actions, leading to the formation of sheets lying parallel to (010) for (I) and (001) for (II). The absolute structure of compound (II) was determined by resonant scattering [Flack parameter = 0.088 (14)].

Conformational isomerism in solid state of AMG 853--structure studies using solid-state nuclear magnetic resonance and X-ray diffraction

Investigation of an additional resonance peak in the (19) F solid-state nuclear magnetic resonance (NMR) spectrum of AMG 853, a dual antagonist of DP and CRTH2 previously in clinical development for asthma, has led to the identification of two conformational isomers coexisting in the crystal lattice in a continuous composition range between 89.7%:10.3% and 96.5%:3.5%. These two isomers differ in the chloro-flurorophenyl moiety orientation-the aromatic ring is flipped by 180° in these two isomers. The level of the minor isomer is directly measured through integration of the two peaks in the (19) F solid-state NMR spectrum. The values obtained from the NMR data are in excellent agreement with the degree of disorder of the fluorine atom in the crystal structure, refined using both single-crystal and high-resolution powder X-ray diffraction data.

Crystal structure of penta-kis-(ethyl-enedi-amine-κ(2) N,N')lanthanum(III) trichloride-ethylene-diamine-dichloromethane (1/1/1)

We report here the crystal structure of a ten-coordinate lanthanum(III) metal coordinated by five bidentate ethyl-enedi-amine ligands, [La(C2H8N2)5]Cl3·C2H8N2·CH2Cl2. One free ethyl-enedi-amine mol-ecule and three Cl(-) anions are also located in the asymmetric unit. The overall structure is held together by an extensive hydrogen-bonding network between the Cl(-) anions and the NH groups on the metal-bound ethyl-enedi-amine ligands. The free ethyl-enedi-amine mol-ecule is held in an ordered position by additional hydrogen bonds involving both the chlorides and -NH groups on the metal-bound ligands. One highly disordered mol-ecule of di-chloro-methane is located on an inversion center; however, all attempts to model this disorder were unsuccessful. The electron density in this space was removed using the BYPASS procedure [van der Sluis & Spek (1990 ▶). Acta Cryst. A46, 194-201].

Crystal structure of a samarium(III) nitrate chain cross-linked by a bis-carbamoyl-methyl-phosphine oxide ligand

In the title compound poly[aqua-bis-(μ-nitrato-κ(4) O,O':O,O'')tetra-kis-(nitrato-κ(2) O,O'){μ4-tetra-ethyl [(ethane-1,2-diyl)bis(aza-nedi-yl)bis-(2-oxo-ethane-2,1-di-yl)]di-phospho-nate-κ(2) O,O'}disamarium(III)], [Sm2(NO3)6(C14H30N2O8P2)(H2O)] n , a 12-coordinate Sm(III) and a nine-coordinate Sm(III) cation are alternately linked via shared bis-bidentate nitrate anions into a corrugated chain extending parallel to the a axis. The nine-coordinate Sm(III) atom of this chain is also chelated by a bidentate, yet flexible, carbamoyl-methyl-phoshine oxide (CMPO) ligand and bears one water mol-ecule. This water mol-ecule is hydrogen bonded to nitrate groups bonded to the 12-coordinate Sm(III) cation. The CMPO ligand, which lies about an inversion center, links neighboring chains along the c axis, forming sheets parallel to the ac plane. Hydrogen bonds between the amide NH group and metal-bound nitrate anions are also present in these sheets. The sheets are packed along the b axis through only van der Waals inter-actions.

2,2'-Bi[benzo[b]thiophene]: an unexpected isolation of the benzo[b]thiophene dimer

The crystal structure of 2,2'-bi[benzo[b]thiophene], C16H10S2, at 173 K has triclinic (P1) symmetry. It is of interest with respect to its apparent mode of synthesis, as it is a by-product of a Stille cross-coupling reaction in which it was not explictly detected by spectroscopic methods. It was upon crystal structure analysis of a specimen isolated from the mother liquor that this reaction was determined to give rise to the title compound, which is a dimer arising from the starting material. Two independent half-molecules of this dimer comprise the asymmetric unit, and the full molecules are generated via inversion centers. Both molecules in the unit cell exhibit ring disorder, and they are essentially identical because of their rigidity and planarity.

The iso-VAPOL ligand: synthesis, solid-state structure and its evaluation as a BOROX catalyst

The iso-VAPOL ligand is just as effective as VAPOL in the catalytic asymmetric synthesis of aziridines at one-tenth the cost.

Kinetic resolution of unsaturated amides in a chlorocyclization reaction: concomitant enantiomer differentiation and face selective alkene chlorination by a single catalyst

The first example of a kinetic resolution via chlorofunctionalization of olefins is reported. The enantiomers of racemic unsaturated amides were found to have different hydrogen-bonding affinities for chiral Lewis bases in numerous solvents. This interaction was exploited in developing a kinetic resolution of racemic unsaturated amides via halocyclization. The same catalyst serves to both "sense chirality" in the substrate as well as mediate a highly face-selective chlorine delivery onto the olefin functionality, resulting in stereotriad products in up to 99:1 dr and up to 98.5:1.5 er. The selectivity factors were typically greater than 50 to allow for the simultaneous synthesis of both the products and unreacted substrates in highly enantioenriched form at yields approaching 50%. The reaction employs catalytic amounts (≤0.50 mol %) of a commercially available and recyclable organocatalyst.

Single-site N-N bond cleavage by Mo(IV): possible mechanisms of hydrazido(1-) to nitrido conversion

Mo(NMe(2))(4) and the tridentate, dipyrrolyl ligand H(2)dpma(mes) were found to form 5-coordinate Mo(NMe(2))(2)(dpma(mes)) (1), which exhibits spin-crossover behaviour in solution. The complex is a ground state singlet with a barrier of 1150 cm(-1) for production of the triplet in d(8)-toluene. The complex reacts with 1,1-disubstituted hydrazines or O-benzylhydroxylamine to produce nitrido MoN(NMe(2))(dpma(mes)). The mechanism of the 1,1-dimethylhydrazine reaction with 1 was examined along with the mechanism of substitution of NMe(2) with H(2)NNMe(2) in a diamagnetic zirconium analogue. The proposed mechanism involves production of a hydrazido(1-) intermediate, Mo(NMe(2))(NHNMe(2))(dpma(mes)), which undergoes an α,β-proton shift and N-N bond cleavage with metal oxidation to form the nitrido. The rate law for the reaction was found to be -d[1]/dt = k(obs)[1][hydrazine] by initial rate experiments and examination of the full reaction profile. This conversion from hydrazido(1-) to nitrido is somewhat analogous to the proposed mechanism for O-O bond cleavage in some peroxidases.

Optimization of tricyclic Nec-3 necroptosis inhibitors for in vitro liver microsomal stability

Necroptosis is a regulated caspase-independent cell death pathway with morphological features resembling passive non-regulated necrosis. Several diverse structure classes of necroptosis inhibitors have been reported to date, including a series of 3,3a,4,5-tetrahydro-2H-benz[g]indazoles (referred to as the Nec-3 series) displaying potent activity in cellular assays. However, evaluation of the tricyclic necroptosis inhibitor's stability in mouse liver microsomes indicated that they were rapidly degraded. A structure-activity relationship (SAR) study of this compound series revealed that increased liver microsomal stability could be accomplished by modification of the pendent phenyl ring and by introduction of a hydrophilic substituent (i.e., α-hydroxyl) to the acetamide at the 2-position of the tricyclic ring without significantly compromising necroptosis inhibitory activity. Further increases in microsomal stability could be achieved by utilizing the 5,5-dioxo-3-phenyl-2,3,3a,4-tetrahydro-[1]benzothiopyrano[4,3-c]pyrazoles. However, in this case necroptosis inhibitory activity was not maintained. Overall, these results provide a strategy for generating potent and metabolically stable tricyclic necrostatin analogs (e.g., 33, LDN-193191) potentially suitable for in vivo studies.

Absolute configuration for 1,n-glycols: a nonempirical approach to long-range stereochemical determination

The absolute configurations of 1,n-glycols (n = 2-12, 16) bearing two chiral centers were rapidly determined via exciton-coupled circular dichroism (ECCD) using a tris(pentafluorophenyl)porphyrin (TPFP porphyrin) tweezer system in a nonempirical fashion devoid of chemical derivatization. A unique "side-on" approach of the porphyrin tweezer relative to the diol guest molecule is suggested as the mode of complexation.

Oxygen atom transfer mediated by an iron(IV)/iron(II) macrocyclic complex containing pyridine and tertiary amine donors

A new non-heme iron model complex containing a high-spin iron(II) complexed with N-methylated pyridine-containing macrocycle was synthesized and crystallographically characterized. The complex generates peroxo- and high-valent iron-oxo intermediates in reactions with tert-butylhydroperoxide and isopropyl 2-iodoxybenzoate, respectively, allowing to gain insight into the formation and reactivity of enzyme-like intermediates related to biological oxygen activation. The formation and reactivity of these intermediate species were investigated by the stopped-flow methodology. The mechanism of oxygen transfer to organic substrates involving reaction of oxoiron(IV) intermediate was elucidated on the basis of spectroscopic and kinetic data. Incorporation of a pyridine ring into the macrocycle increased the reactivity of the Fe(IV)=O intermediates in comparison with polyamine tetraaza macrocyclic complexes: ferryl (Fe(IV)=O) species derived from 3 demonstrated electrophilic reactivity in transferring an oxygen atom to substituted triarylphosphines and to olefins (such as cyclooctene). However, iron(III) alkylperoxo intermediate was unreactive with cyclooctene.

Evaluation of donor and steric properties of anionic ligands on high valent transition metals

Synthetic protocols and characterization data for a variety of chromium(VI) nitrido compounds of the general formula NCr(NPr(i)(2))(2)X are reported, where X = NPr(i)(2) (1), I (2), Cl (3), Br (4), OTf (5), 1-adamantoxide (6), OSiPh(3) (7), O(2)CPh (8), OBu(t)(F6) (9), OPh (10), O-p-(OMe)C(6)H(4) (11), O-p-(SMe)C(6)H(4) (12), O-p-(Bu(t))C(6)H(4) (13), O-p-(F)C(6)H(4) (14), O-p-(Cl)C(6)H(4) (15), O-p-(CF(3))C(6)H(4) (16), OC(6)F(5) (17), κ(O)-N-oxy-phthalimide (18), SPh (19), OCH(2)Ph (20), NO(3) (21), pyrrolyl (22), 3-C(6)F(5)-pyrrolyl (23), 3-[3,5-(CF(3))(2)C(6)H(3)]pyrrolyl (24), indolyl (25), carbazolyl (26), N(Me)Ph (27), κ(N)-NCO (28), κ(N)-NCS (29), CN (30), NMe(2) (31), F (33). Several different techniques were employed in the syntheses, including nitrogen-atom transfer for the formation of 1. A cationic chromium complex [NCr(NPr(i)(2))(2)(DMAP)]BF(4) (32) was used as an intermediate for the production of 33, which was produced by tin-catalyzed degredation of the salt. Using spin saturation transfer or line shape analysis, the free energy barriers for diisopropylamido rotation were studied. It is proposed that the estimated enthalpic barriers, Ligand Donor Parameters (LDPs), for amido rotation can be used to parametrize the donor abilities of this diverse set of anionic ligands toward transition metal centers in low d-electron counts. The new LDPs do not correlate well to the pK(a) value of X. Conversely, the LDP values of phenoxide ligands do correlate with Hammett parameters for the para-substituents. Literature data for (13)C NMR chemical shifts for a tungsten-based system with various X ligands plotted versus LDP provided a linear fit. In addition, the angular overlap model derived e(σ) + e(π) values for chromium(III) ammine complexes correlate with LDP values. Also discussed is the correlation with XTiCp*(2) spectroscopic data. X-ray diffraction has been used used to characterize 31 of the compounds. From the X-ray diffraction data, steric parameters for the ligands using the Percent Buried Volume and Solid Angle techniques were found.

Synthesis of a new class of β-iodo N-alkenyl 2-pyridones

A new method for the synthesis of β-iodo N-alkenyl 2-pyridones from substituted 2-propargyloxypyridines has been discovered . These compounds present a unique complement of orthogonal functionality and structural characteristics that are unavailable via other routes. The ready access to these compounds renders them an important entry point for the preparation of more complex N-alkyl pyridone-containing targets.

Selectivity in the addition reactions of organometallic reagents to aziridine-2-carboxaldehydes: the effects of protecting groups and substitution patterns

Good to excellent stereoselectivity has been found in the addition reactions of Grignard and organozinc reagents to N-protected aziridine-2-carboxaldehydes. Specifically, high syn selectivity was obtained with benzyl-protected cis, tert-butyloxycarbonyl-protected trans, and tosyl-protected 2,3-disubstituted aziridine-2-carboxaldehydes. Furthermore, rate and selectivity effects of ring substituents, temperature, solvent, and Lewis acid and base modifiers were studied. The diastereomeric preference of addition is dominated by the substrate aziridines' substitution pattern and especially the electronic character and conformational preferences of the nitrogen protecting groups. To help rationalize the observed stereochemical outcomes, conformational and electronic structural analyses of a series of model systems representing the various substitution patterns have been explored by density functional calculations at the B3LYP/6-31G* level of theory with the SM8 solvation model to account for solvent effects.

A second polymorph of chlorido(hydroxy-diphenyl-phosphane)gold(I)

The title complex, [AuCl{(C(6)H(5))(2)P(OH)-κP}] or [AuCl(C(12)H(11)OP)], contains two independent mol-ecules in the asymmetric unit and is a polymorph of a previously reported structure [Hollatz et al. (1999 ▶) J. Chem. Soc. Dalton Trans. pp. 111-114]. The crystal structure exhibits inter-molecular Au⋯Au inter-actions with alternate distances of 3.0112 (3) Å and 3.0375 (2) Å. The Cl-Au-P bond angle varies between different mol-ecular units, depending on the degree of influence of the intra-molecular the O-H⋯Cl hydrogen bond; the angle thus varies between negligible distortion from linearity at 179.23 (3)° and more significant distortion at 170.39 (4)°, which differs from the previously reported polymorph in which both these angles are approximately 170°. The Au-Cl [2.3366 (9) and 2.3131 (10)Å] and Au-P [2.2304 (10) and 2.2254 (10) Å] bond lengths vary slightly between the two independent mol-ecules but overall, the bond lengths are in good agreement with those in the previously reported polymorph.

Bis[bis(diphenylphosphinoyl)acetonitrile-κ2O,O′]copper(II)

The title complex, [Cu(C₂₆H₂₀NO₂P₂)₂], contains a central Cu^II atom surrounded by two homoleptic bidentate ligands, which form two five-membered chelate rings. The Cu atom binds to four O atoms, resulting in a four-coordinate square-planar complex. The asymmetric unit contains half of the complex, the other half being completed by inversion symmetry. The Cu—O bond lengths have similar distances, viz. 1.9153 (10) Å for the pair opposite (trans) each other and 1.9373 (10) Å for the other (trans) pair. The P—O bond lengths are 1.5250 (11) Å, indicating significant electron delocalization across the O—P—C—P—O atoms in the chelate ring, resulting in a longer P—O bond length when compared to a formal double-bond P=O character (much shorter at approximately 1.47 Å). The two inter­secting O—Cu—O angles are both linear at 180°, whilst the remaining L-shaped O—Cu—O bond angles are 88.26 (5) and 91.74 (5)°. The C—C N fragment is slightly distorted from linearity at 177.44 (19)° and the C N bond length of 1.151 (2) Å indicates predominantly triple-bond character.

The Effect of Excess Carbon on the Crystallographic, Microstructural, and Mechanical Properties of CVD Silicon Carbide Fibers

Silicon carbide (SiC) fibers made by chemical vapor deposition (CVD) are of interest for organic, ceramic, and metal matrix composite materials due their high strength, high elastic modulus, and retention of mechanical properties at elevated processing and operating temperatures. The properties of SCS-6™ silicon carbide fibers, which are made by a commercial process and consist largely of stoichiometric SiC, were compared with an experimental carbon-rich CVD SiC fiber, to which excess carbon was added during the CVD process. The concentration, homogeneity, and distribution of carbon were measured using energy dispersive x-ray spectroscopy (SEM/EDS). The effect of excess carbon on the tensile strength, elastic modulus, and the crystallographic and microstructural properties of CVD silicon carbide fibers was investigated using tensile testing, x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

On the chlorenium source in the asymmetric chlorolactonization reaction

N-Acylated N-chlorohydantoins are shown to be competent chlorenium sources in the (DHQD)(2)PHAL-mediated asymmetric chlorolactonization. The derivatives demonstrate the exact role of the N1 and N3 chlorine atoms in the parent dichlorohydantoins with the N1 chlorine serving as an inductive activator and the N3 chlorine being delivered to the substrate. The putative associated catalyst/chlorine source complex was experimentally demonstrated through a series of matched/mismatched experiments employing chiral N-chlorinated hydantoins.

[μ-Bis(diphenylphosphanyl)acetonitrile-κ2P:P]bis[chloridogold(I)]

The title complex, [Au₂Cl₂(C₂₆H₂₁NP₂)], has an intra­molecular Au⋯Au inter­action of 3.1669 (4) Å, but no inter­molecular Au⋯Au inter­actions in the solid state. The Cl—Au—P bond angle of 176.84 (7)° is slightly distorted from linearity. The P—C bond length to the phenyl group is shorter [1.810 (7) Å] than the P—C bond length [1.876 (7) Å] to the bridging carbon, indicative of the flexibility of the bidentate bite of the ligand. The C—C N fragment is essentially linear at 179.5 (9)° and the C N bond length of 1.125 (11) Å indicates predominantly triple-bond character. In the crystal packing, there are no hydrogen-bonding or aurophilic inter­actions between the mol­ecules.

(Ferrocenyl-thio-phospho-nato-κS)(triphenyl-phosphane-κP)gold(I) dichloro-methane monosolvate

In the title compound, [AuFe(C₅H₅)(C₅H₅O₂PS)(C₁₈H₁₅P)]·CH₂Cl₂, the two-coordinate gold(I) atom shows a slightly distorted linear arrangement, with a P—Au—S bond angle of 176.81 (6)°. The difference in P=O and P—O(H) bond lengths, which are 1.503 (6) and 1.541 (5) Å, respectively, implies there is apparently no delocalization between the P—O bonds, and the proton appears to be localized on one O atom only. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds link dinuclear mol­ecules into chains propagated in the [010] direction. The dichloro­methane solvent mol­ecule was disordered between two positions in a 0.63 (3):0.37 (3) ratio.

Electronic effects in iridium C-H borylations: insights from unencumbered substrates and variation of boryl ligand substituents

Experiment and theory favour a model of C-H borylation where significant proton transfer character exists in the transition state.

Getting the sterics just right: a five-coordinate iridium trisboryl complex that reacts with C-H bonds at room temperature

Five-coordinate boryl complexes relevant to Ir mediated C-H borylations have been synthesized, providing a glimpse of the most fundamental step in the catalytic cycle for the first time.