Synthesis and spectroscopic characterization of cadmium(II) complexes of thiones and thiocyanate

Cadmium(II) complexes of thiones and thiocyanate, [(>C=S)₂Cd(SCN)₂], have been prepared and characterized by IR and NMR spectroscopy. An upfield shift in the >C=S resonance of thiones in the ¹³C NMR and downfield shift in N–H resonance in ¹H NMR are consistent with sulfur coordination to cadmium(II). The presence of ν(N–H) of thiones in IR spectra of the complexes indicates the thione forms of the ligands in the solid state; some contribution of the thiolate form was observed in one complex. The appearance of a band around 2100 cm^?1 in IR and a resonance around 132 ppm in ¹³C NMR indicates the binding of thiocyanate to cadmium(II).     

Nitrosylated iron-thiolate-sulfinate complexes with {Fe(NO)}6/7 electronic cores: relevance to the transformation between the active and inactive NO-bound forms of iron-containing nitrile hydratases

The five-coordinated iron-thiolate nitrosyl complexes [(NO)Fe(S,S-C6H3R)2]- (R = H (1), m-CH3 (2)), [(NO)Fe(S,S-C6H2-3,6-Cl2)2]- (3), [(NO)Fe(S,S-C6H3R)2]2- (R = H (10), m-CH3 (11)), and [(NO)Fe(S,S-C6H2-3,6-Cl2)2]2- (12) have been isolated and structurally characterized. Sulfur oxygenation of iron-thiolate nitrosyl complexes 1-3 containing the {Fe(NO)}6 core was triggered by O2 to yield the S-bonded monosulfinate iron species [(NO)Fe(S,SO2-C6H3R)(S,S-C6H3R)]- (R = H (4), m-CH3 (5)) and [(NO)Fe(S,SO2-C6H2-3,6-Cl2)(S,S-C6H2-3,6-Cl2)]2(2-) (6), respectively. In contrast, attack of O2 on the {Fe(NO)}7 complex 10 led to the formation of complex 1 accompanied by the minor products, [Fe(S,S-C6H4)2]2(2-) and [NO3]- (yield 9%). Reduction of complexes 4-6 by [EtS]- in CH3CN-THF yielded [(NO)Fe(S,SO2-C6H3R)(S,S-C6H3R)]2- (R = H (7), m-CH3 (8)) and [(NO)Fe(S,SO2-C6H2-3,6-Cl2)(S,S-C6H2-3,6-Cl2)]2- (9) along with (EtS)2 identified by 1H NMR. Compared to complex 10, complexes 7-9 with the less electron-donating sulfinate ligand coordinated to the {Fe(NO)}7 core were oxidized by O2 to yield complexes 4-6. Obviously, the electronic perturbation of the {Fe(NO)}7 core caused by the coordinated sulfinate in complexes 7-9 may serve to regulate the reactivity of complexes 7-9 toward O2. The iron-sulfinate nitrosyl species with the {Fe(NO)}6/7 core exhibit the photolabilization of sulfur-bound [O] moiety. Complexes 1-4-7-10 (or 2-5-8-11 and 3-6-9-12) are interconvertible under sulfur oxygenation, redox processes, and photolysis, respectively.     

Methylmercury and dimethylthallium complexes of 5-(4′-dimethylaminobenzylidene)-2-thiohydantoin (HDABTd): The crystal and molecular structures of HDABTd and [TlMe2(DABTd)(DMSO)]

The ligand 5-(4′-dimethylaminobenzylidene)-2-thiohydantoin (HDABTd) was prepared and its structure determined by X-ray diffraction. In the crystal, ligand molecules are linked in chains along the [110] direction by intermolecular N(3)–H(3)O(1)^I and N(1)–H(1)Sⁱⁱ hydrogen bonds. The complexes [HgMe(DABTd)] and [TlMe₂(DABTd)] were prepared by reaction of the ligand with methylmercury acetate or dimethylthallium hydroxide, and were characterized in the solid state by IR spectroscopy and in solution by conductivity measurements and ¹H, ¹³C, ¹⁹⁹Hg and ²⁰⁵Tl NMR spectroscopy. The dimethylthallium complex crystallized in DMSO solution as [TlMe₂(DABTd)(DMSO)], an X-ray diffraction study of which showed its thallium atoms to be coordinated to the two methyl C atoms, the oxygen atom of a DMSO molecule, the S and N(1) atoms of one DABTd ligand and, more weakly, to the oxygen atom of a neighbouring DABTd. This last interaction links the molecules of the complex in chains parallel to the b axis. Crystals of the methylmercury(II) complex contain three [HgMe(DABTd)]·DMSO structures per asymmetric unit, but poor data quality prevented complete refinement.     

一维链状三环己基锡羧酸酯的合成、晶体结构及生物活性

本文以含酯基刚性一元酸L1H(8-乙氧羰基-1-萘甲酸)和含羰基柔性一元酸L2H(4-羰基-4-苯基丁酸)作为多齿配体,分别与三环己基氢氧化锡发生自组装反应,获得了2个新型三环己基锡羧酸酯配合物[(C6H11)3SnL1](1)和[(C6H11)3SnL2](2)(C6H11为环己基)。采用元素分析、1H NMR、FTIR及晶体结构测定等手段对配合物1和2进行了结构表征,在2个新配合物中,锡原子均为六配位,构成以锡原子为中心的扭曲单加帽三角双锥构型,并且通过O→Sn分子间配位键形成了一维超分子链。初步研究了杀菌活性和抗癌活性。     

Organotin(IV) derivatives as biocides: An investigation of structure by IR, solution NMR, electron impact MS and assessment of structure correlation with biocidal activity

A brief account is given of the synthesis, structural chemistry and the antibacterial, antifungal and cytotoxic effects of organotin complexes of 2-[(2,4-dichloroanilinocarbonyl)]benzoic acid. The unimolar and bimolar substitution products have been characterized by elemental analysis and spectral studies, including IR, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR, and mass spectra. The data support the binding of the oxygen atom to the tin atom in [R₂Sn(OOCR’)₂] and [R₃Sn(OOCR’)] (R = Me, Bu, and Ph, R’ = 2-[(2,4-dichloroanilinocarbonyl)]benzoic acid). Based on these studies, with a coordination number of four, a distorted tetrahedral geometry has been proposed for the resulting derivatives in solution. The free ligand (R’/COOH) and its respective tin complexes were tested in vitro against a number of microorganisms to assess their biocidal properties and to correlate them with the structures of the derivatives.     

Anomalous stereochemistry of pyrazolato-3,5-dicarboxylato-bridged dinuclear chromate(III) complexes containing ethylenediamine-N,N'-dicarboxylates with entrapped unstable conformations: X-ray structure of Na[Cr2(eddp)(mu-pzdc)].6H2O

Several new pyrazolato-3,5-dicarboxylato (pzdc) bridged dinuclear chromate(III) complexes containing linear tetradentate O-N-N-O type ligands were synthesized and structurally characterized. Among them, the X-ray structure of the eddp complex Na[Cr2(eddp)(mu-pzdc)].6H2O (eddp = ethylenediamine-N,N'-dipropionate) was determined to have a (sym-cis)-(unsym-cis) geometrical configuration with intramolecular three-center hydrogen bonds, entrapping the unfavored sym-cis configuration for the Cr(eddp) moiety as well as the favored unsym-cis one. As a pair of positional disorders, there were also found to be two conformational isomers with respect to the absolute configurations of the coordinated asymmetric nitrogen atom at the G (in-plane) ring for the unsym-cis moiety. Moreover, chiral pzdc-bridged dinuclear complexes with another type of O-N-N-O ligand, 1,2-cyclohexanediamine-N,N'-diacetate (cdda), were successfully synthesized, isolated, and characterized by column chromatographic behavior, elemental analysis, and chiroptical spectra. There were two diastereomers for Na[(R,R-cdda)Cr(mu-pzdc)Cr(S,S-cdda)] and only one isomer for Na[(R,R-cdda)Cr(mu-pzdc)Cr(R,S-cdda)] and Na[(R,R-cdda)Cr(mu-pzdc)Cr(edda)] (R,R- or S,S- and R,S-cdda = R,R-trans- or S,S-trans- and R,S-cis-1,2-cyclohexanediamine-N,N'-diacetate, and edda = ethylenediamine-N,N'-diacetate). From their circular dichroism (CD) spectra, these complexes could exhibit the delta-delta absolute configuration with ((sym-cis-R,R-cdda)-(unsym-cis-edda or S,S- or R,S-cdda)) geometrical configuration, indicating the abnormal eq-eq (N-Ceq) configuration for the R,R-cdda. The comparison among the CD spectra of the ((cdda)-(cdda)) complexes revealed that two diastereomers of the ((R,R-cdda)-(S,S-cdda)) complex correspond to the conformational isomers resulting from the difference in geometrical orientations of the secondary amine protons on two coordinated asymmetric nitrogen atoms with the opposite absolute configuration in the unsym-cis-S,S-cdda moiety. In a series of the pzdc-bridged Cr(III) complexes the anomalous conformations in two different geometrical configurations could be entrapped probably owing to stereognostic coordination through the intramolecular N-H...O hydrogen bond interaction.     

High-performance liquid chromatographic enantioseparation of (R,S)-fluoxetine using Marfey's reagent and (S)-N-(4-nitrophenoxycarbonyl) phenylalanine methoxyethyl ester as chiral derivatizing reagents along with direct thin-layer chromatographic resolution and isolation of enantiomers using L-tartaric acid as mobile phase additive

Chiral assay of enantiomers of fluoxetine was achieved in pharmaceutical formulations using direct and indirect methods. L-tartaric acid was used as a mobile phase additive in thin-layer chromatography; the enantiomers were separated and isolated and were used to determine the elution order in HPLC. (R,S)-flouxetine was derivatized with (S)-N-(4-nitrophenoxycarbonyl)phenylalanine methoxyethyl ester [(S)-NIFE], Marfey's reagent and 1-fluoro-2,4-dinitrophenyl-L-methionine amide (FDNP-L-Met-NH?. The diastereomers were separated using RP-HPLC. The effect of flow rate and TFA concentration on resolution was studied. The diastereomers obtained by derivatization with FDNP-L-Met-NH? were also separated by RP-TLC.     

Synthesis and characterization of diiron dithiolate complexes containing a quinoxaline bridge

A potential model complex for the hydrogenase active site, [Fe(2){(μ-CH(2)S)(2)R}(CO)(6)] (1) (R = quinoxaline), was synthesized by condensation of [(μ-LiS)(2)Fe(2)(CO)(6)] with 2,3-bis(bromomethyl)quinoxaline. Reactions of 1 with bis(diphenylphosphino)methane (dppm) under a range of conditions yielded substituted complexes [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)(dppm)] (2), [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(k(2)-dppm)] (3) and [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(μ-dppm)] (4). X-ray crystallography confirms that in 2, the dppm is terminally bonded to an iron atom via one phosphorus atom, whereas in 3, it acts as a chelating ligand to coordinate to an iron center in a dibasal-substituted manner. In 4, the dppm bridges the two iron atoms in a cis basal/basal fashion with one phosphorus bonded to each iron atom. Treatment of 1 with various tertiary phosphines at room temperature in acetonitrile (MeCN) generates a range of mono-substituted products [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)L] (5, L = PEt(3); 6, PMe(3); 7, PPh(3); 8, Me(2)PPh). With Bu(t)NC, mono- and di-substituted [Fe(2){(μ-CH(2)S)(2)R}(CO)(5)(Bu(t)NC)] (9) and [Fe(2){(μ-CH(2)S)(2)R}(CO)(4)(Bu(t)NC)(2)] (10) complexes are generated. All the complexes were characterized by elemental analysis, IR, MS and NMR spectroscopy. IR and NMR spectroscopic studies suggest that addition of excess HBF(4)·OEt(2) acid to 1-4 led to the protonation of quinoxaline nitrogen atoms. In contrast, 5-10 were not stable in acidic media. Electrochemistry of 1-4 was investigated in the acetonitrile medium (0.1 M Bu(4)NPF(6)). The electrochemical instability of the reduced ligand, quinoxaline, and the reduced forms of these complexes revealed from the electrochemical studies suggests that they do not provide ideal models of the hydrogenase active site.     

MONO-ORGANOMERCURY AND DIORGANOTHALLIUM DERIVATIVES OF THIOHYDANTOIN AND 5-(BENZYLIDENE)-2-THIOHYDANTOIN: THE CRYSTAL STRUCTURE OF DIMETHYL-[5-(BENZYLIDENE)-2-THIOHYDANTOINATO]-THALLIUM(III)

Abstract

The complexes [TlR₂(Td)], [TlR₂(BTd)], [HgR(Td)] and [HgR(BTd)] (R = Me, Ph; HTd = thiohydantoin; HBTd = 5-(benzylidene)-2-thiohydantoin) were prepared by reacting the appropriate ligand with the appropriate diorganothallium hydroxide or mono-organomercury acetate. They have been studied in the solid state (by vibrational spectroscopy and mass spectrometry) and in solution (by using NMR). In addition, the crystal structure of [TlMe₂(BTd)] has been determined by X-ray diffraction. The crystals have a polymeric structure in which each thallium atom is coordinated to the two methyl C atoms, the S and N atoms of one BTd ligand. the S atom of another and the O atom of a third. The coordination modes of the two ligands in the other complexes are discussed on this basis in the light of spectroscopic data.     

Application of P-stereogenic aminophosphine phosphinite ligands in asymmetric hydroformylation

New chiral aminophosphine phosphinite ligands with a stereogenic center at the aminophosphine phosphorus atom were prepared based on (R,S)-ephedrine as the chiral auxiliary and backbone. Substituents at the chiral aminophosphine as well as at the phosphinite phosphorus atom were varied. These new ligands were applied to the rhodium-catalyzed asymmetric hydroformylation of vinyl arenes. The enantiomeric excess reached up to 77%. 1H and 31P NMR studies of the Rh complexes under syngas pressure reveal that [HRh(CO)2(PP)] complexes with the NP* moiety in an axial position are responsible for enantioselectivity.     

Synthesis and Anti-inflammatory Action of(η-C5H5)2Ti(Sal)2 and (η-C5H5)2Ti(Clo)2

Two new complexes (Cp)2Ti(Sal)2 and(Cp)2Ti(Clo)2(Cp=Cyclopentadienyl η5-C5H5), have been synthesized in anhydrous THF by the reaction of Hsal(o-hydroxybenzoic acid, salicylate acid) or Hclo[N-(m-chloro-phe-nyl) anthranili acid, acidum clofenamicum] with (Cp)2TiCl2 and characterized by means of elemental analyses, IR, 1H NMR, 13C NMR, UV and molar conductivity. In complex (Cp)2Ti(Sal)2 or (Cp)2Ti(Clo)2, the oxygen atom of the carboxyl group coordinates to Ti(IV) in a monodentate manner. The inhibitory action of the complexes on mouse ear tumefaction caused by croton oil and rat foot granulation growth caused by cotton balls is higher than that of the corresponding ligands Hsal, Hclo and [(Cp)2TiCl2], whereas their toxicity is lower than those of the free ligands.     

Chiral discrimination studies of (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid by high-performance liquid chromatography and NMR spectroscopy

Chiral discrimination studies using (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA) as a chiral selector were performed by high-performance liquid chromatography (HPLC) and NMR spectroscopy. The enantiomers of alanine (Ala) or alanine methyl ester (Ala-ME) were well separated on the chiral stationary phases (CSPs) derived from (+)-18-C-6-TA by HPLC. The chiral selector, (+)-18-C-6-TA, used in the CSP was also applied for the chiral discrimination of the Ala and Ala-ME enantiomers, and it discriminated these enantiomers successfully by NMR spectroscopy. The chemical shift differences (Delta Delta delta) of the alpha-proton of these enantiomers in the presence of an equimolecular solution of 18-C-6-TA were observed to be 0.10 ppm for Ala in methanol-d4 containing 10 mM H2SO4 and 0.11 ppm for Ala-ME in methanol-d4. The observed NMR results agreed with the chromatographic data on the (+)-18-C-6-TA-derived CSP by HPLC in terms of both the elution order and solvents effects.     

Physicochemical characterization of the dimeric lanthanide complexes [en{Ln(DO3A)(H2O)}2] and [pi{Ln(DTTA)(H2O)}2]2-: a variable-temperature 17O NMR study

The Gd(III) complexes of the two dimeric ligands [en(DO3A)2] {N,N'-bis[1,4,7-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecan-10-yl-methylcarbonyl]-N,N'-ethylenediamine} and [pi(DTTA)2]8- [bisdiethylenetriaminepentaacetic acid (trans-1,2-cyclohexanediamine)] were synthesized and characterized. The 17O NMR chemical shift of H2O induced by [en{Dy(DO3A)}2] and [pi{Dy(DTTA)}2]2- at pH 6.80 proved the presence of 2.1 and 2.2 inner-sphere water molecules, respectively. Water proton spin-lattice relaxation rates for [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- at 37.0 +/- 0.1 degrees C and 20 MHz are 3.60 +/- 0.05 and 5.25 +/- 0.05 mM(-1) s(-1) per Gd, respectively. The EPR transverse electronic relaxation rate and 17O NMR transverse relaxation time for the exchange lifetime of the coordinated H2O molecule and the 2H NMR longitudinal relaxation rate of the deuterated diamagnetic lanthanum complex for the rotational correlation time were thoroughly investigated, and the results were compared with those reported previously for other lanthanide(III) complexes. The exchange lifetimes for [en{Gd(DO3A)(H2O)}2] (769 +/- 10 ns) and [pi{Gd(DTTA)(H2O)}2]2- (910 +/- 10 ns) are significantly higher than those of [Gd(DOTA)(H2O)]- (243 ns) and [Gd(DTPA)(H2O)]2- (303 ns) complexes. The rotational correlation times for [en{Gd(DO3A)(H2O)}2] (150 +/- 11 ps) and [pi{Gd(DTTA)(H2O)}2]2- (130 +/- 12 ps) are slightly greater than those of [Gd(DOTA)(H2O)]- (77 ps) and [Gd(DTPA)(H2O)]2- (58 ps) complexes. The marked increase in relaxivity (r1) of [en{Gd(DO3A)(H2O)}2] and [pi{Gd(DTTA)(H2O)}2]2- result mainly from their longer rotational correlation time and higher molecular weight.     

Pyrrole-appended derivatives of O-confused oxaporphyrins and their complexes with nickel(II), palladium(II), and silver(III)

Condensation of 2,4-bis(phenylhydroxymethyl)furan with pyrrole and p-toluylaldehyde formed, instead of the expected 5,20-diphenyl-10,15-di(p-tolyl)-2-oxa-21-carbaporphyrin, a pyrrole addition product [(H,pyr)OCPH]H(2); this product can formally be considered as an effect of hydrogenation of 3-(2'-pyrrolyl)-5,20-diphenyl-10,15-di(p-tolyl)-2-oxa-21-carbaporphyrin ([(pyr)OCPH]H). The new oxacarbaporphyrinoid presents the (1)H NMR spectroscopy features of an aromatic molecule, including the upfield shift of the inner H21 atom. Insertion of NiCl(2) or PdCl(2) into [(H,pyr)OCPH]H(2) gave two structurally related organometallic complexes, [(pyr)OCP]Ni(II)] and [(pyr)OCP]Pd(II)], in which the metal ions are bound by three pyrrolic nitrogens and the trigonally hybridized C21 atom of the inverted furan. The reaction of [(H,pyr)OCPH]H(2) with silver(I) acetate yields a stable Ag(III) complex [(C(2)H(5)O,pyr)OCP]Ag(III)] substituted at the C3 position by the ethoxy and pyrrole moieties. The macrocyclic frame of [(H,pyr)OCPH]H(2) is conserved. Addition of trifluoroacetic acid to [(C(2)H(5)O,pyr)OCP]Ag(III)] yielded a new aromatic complex [(pyr)OCP]Ag(III)](+). The structures of [(pyr)OCP]Ni(II)] and [(C(2)H(5)O,pyr)OCP]Ag(III)] have been determined by X-ray crystallography. In both molecules the macrocycles are only slightly distorted from planarity and the nickel(II) and silver(III) are located in the NNNC plane. The dihedral angle between the macrocyclic and appended-pyrrole planes of [(pyr)OCP]Ni(II)] reflects the biphenyl-like arrangement with the NH group pointing out toward the adjacent phenyl ring on the C5 position. Tetrahedral geometry around the C3 atom was detected for [(C(2)H(5)O,pyr)OCP]Ag(III)]. The Ni[bond]C and Ag[bond]C bond lengths are similar to other nickel(II) or silver(III) carbaporphyrinoids where the trigonal carbon atom coordinates the metal ion. The trend detected in the (13)C chemical shifts for the appended-pyrrole resonances has been rationalized by the extent of effective conjugation between the macrocycle and the appended pyrrole moiety controlled by the hybridization of the C3 atom and the metal ion oxidation state. The dianionic or trianionic macrocyclic core of the pyrrole-appended derivatives is favored to match the oxidation state of nickel(II), palladium(II), or silver(III), respectively.     

Optical resolution and the study of ligand effects on the ortho-metalation reaction of resolved (+/-)-diphenyl[1-(1-naphthyl)ethyl]phosphine and its arsenic analogue

Two highly air-sensitive asymmetric ligands (+/-)-diphenyl[1-(1-naphthyl)ethyl]phosphine and its arsenic analogue [(+/-)-L] have been prepared and resolved by the fractionalization of a pair of diastereomeric palladium complexes containing the appropriate ligand and ortho-metalated (R)-(1-(dimethylamino)ethyl)naphthylene. X-ray structural analysis revealed that the less soluble isomers in each resolution contained the resolving ligand of the S absolute configuration. The resolved ligands coordinated as monodentates with only the phosphorus or arsenic donor coordinated to the resolving organopalladium unit. Due to the steric congestions between the phenyl and the naphthyl rings, the Ph(2)E-C distances in both monodentate ligands are unusually long [1.885(2) A for E = P and 2.035(7) A for E = As]. The (R)-naphthylamine auxiliary could be removed chemoselectively from the resolved complexes by treatment with concentrated hydrochloric acid to give the corresponding bis(micro-chloro) complexes (-)-[(S)-LPdCl(2)](2). Treatments of these dimeric complexes with sodium acetate in ethanol gave the novel ortho-metalated complex bis(micro-chloro)bis[(S)-1-[1-(diphenylphospha)ethyl]naphthylenyl-C(2),P]dipalladium(II), with [alpha](D) +559 degrees (CH(2)Cl(2)), and the analogous ortho-metalated (S)-arsa complex, with [alpha](D) +349 degrees (CH(2)Cl(2)). The Ph(2)E-C distances recorded for the ortho-metalated phosphine complex are 1.841(6) and 1.846(5) A, and those recorded for the organometallic arsa rings are 1.938(9) and 1.945(9) A. These Ph(2)E-C distances are noticeably shorter than those recorded for their analogous monodentate complexes. The intrachelate E-Pd-C angles of the analogous amino, phospha, and arsa complexes involved in the current study are similar [within the range of 80.5(2)-82.1(3) degrees ] although it is noticeable that As > P > N.     

Relation between intramolecular NH...S hydrogen bonds and coordination number in mercury(II) complexes with carbamoylbenzenethiol derivatives

A novel series of bis(carbamoylthiophenolato)mercury(II) complexes, [Hg(S-RNHCOC6H4)2] (1, R = 2-t-Bu; 2, R = 2-CH3; 3, R = 2-C6H5CH2; 4, R = 4-t-Bu), and a tetrakis(carbamoylthiophenolato)mercury(II) complex, (NEt4)2[Hg-(S-2-CH3NHCOC6H4)4] (5), were synthesized and characterized by 1H NMR, IR, 199Hg NMR, and crystallographic analyses. The bis(carbamoylthiophenolato)mercury complexes 1-3 do not have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom coordinated to mercury, whereas the tetrakis(thiophenolato)mercury complex 5 does have an intramolecular NH...S hydrogen bond. A relatively weak NH...S hydrogen bond in 5 can be seen in the 1H NMR spectra and the IR spectra in chloroform and in the solid state. The 199Hg NMR spectra in bis(carbamoylthiophenolato)mercury complexes 1-4 show a downfield shift, with an increase in the flow of electrons to mercury(II) from the oxygen atom due to the intramolecular Hg...O bonding interaction. Conversely, the 199Hg NMR spectra in 5 show a high-field shift with a decrease in the flow of electrons to mercury(II) from the sulfur atom due to the intramolecular NH...S hydrogen bond.     

Gas‐phase interactions of organotin compounds with cysteine

The gas‐phase interactions of cysteine with di‐organotin and tri‐organotin compounds have been studied by mass spectrometry experiments and quantum calculations. Positive‐ion electrospray spectra show that the interaction of di‐ and tri‐organotins with cysteine results in the formation of [(R)₂Sn(Cys‐H)]⁺ and [(R)₃Sn(Cys)]⁺ ions, respectively. MS/MS spectra of [(R)₂Sn(Cys‐H)]⁺ complexes are characterized by numerous fragmentation processes, notably associated with elimination of NH₃ and (C,H₂,O₂). Several dissociation routes are characteristic of each given organic species. Upon collision, both the [(R)₃Sn(Gly)]⁺ and [(R)₃Sn(Cys)]⁺ complexes are associated with elimination of the intact amino acid, leading to the formation of [(R)₃Sn]⁺ cation. But for the latter complex, two additional fragmentation processes are observed, associated with the elimination of NH₃ and C₃H₄O₂S. Calculations indicate that the interaction between organotins and cysteine is predominantly electrostatic but also exhibits a considerable covalent character, which is slightly more pronounced in tri‐organotin complexes. A preferred bidentate interaction of the type ‐η²‐S‐NH₂, with sulfur and the amino group, is observed. As for the [(R)₃Sn(Cys)]⁺ complexes, their stability is due to the combination of the hydrogen bond taking place between the amino group and the sulfur lone pair and the interaction between the carboxylic oxygen atom and the metal. Copyright © 2016 John Wiley & Sons, Ltd.     

Spectroscopic and structural characterization of the charge-transfer interaction of N,N'-bis-alkyl derivatives of 1,4,6,8-naphthalenediimide with chloranilic and picric acids

Charge-transfer (CT) complexes formed from the reactions of two N,N'-bis-alkyl derivatives of 1,4,6,8-naphthalenediimide such as N,N'-bis[2-hydroxyethyl)]-1,4,6,8-naphthalenediimide (BHENDI) and N,N'-bis-[2-N,N-dimethylaminoethyl)]-1,4,6,8-naphthalenediimide (BDMAENDI) with chloranilic acid (CLA) and piciric acid (PA) as pi-acceptors, have been studied spectrophotometrically in methanol and chloroform, respectively at 25 degrees C. The photometric titration curves for the reactions indicated that the data obtained refer to 1:1 charge-transfer complexes of [(BHENDI)(CLA)], [(BDMAENDI)(CLA)], [(BHENDI)(PA)] and [(BDMAENDI)(PA)] were formed. Benesi-Hildebrand and its modification methods were applied to the determination of association constant (K), molar extinction coefficient (varepsilon). The solid CT complexes have been synthesized and characterization by different spectral methods.     

Double stereodifferentiation in the catalytic asymmetric aziridination of imines prepared from α-chiral amines

The catalytic asymmetric aziridination of imines and diazo compounds (AZ reaction) mediated by boroxinate catalysts derived from the VANOL and VAPOL ligands was investigated with chiral imines derived from five different chiral, disubstituted, methyl amines. The strongest matched and mismatched reactions with the two enantiomers of the catalyst were noted with disubstituted methyl amines that had one aromatic and one aliphatic substituent. The synthetic scope for the AZ reaction was examined in detail for α-methylbenzyl amine for cis-aziridines from α-diazo esters and for trans-aziridines from α-diazo acetamides. Optically pure aziridines could be routinely obtained in good yields and with high diastereoselectivity and the minor diastereomer (if any) could be easily separated. The matched case for cis-aziridines involved the (R)-amine with the (S)-ligand, but curiously, for trans-aziridines the matched case involved the (R)-amine with the (R)-ligand for imines derived from benzaldehyde and n-butanal, and the (R)-amine with the (S)-ligand for imines derived from the bulkier aliphatic aldehydes pivaldehyde and cyclohexane carboxaldehyde.     

Chiral resolution of diphenylalanine by high-performance liquid chromatography on a crown-ether-based chiral stationary phase and by NMR spectroscopy

Summary The enantiomers of diphenylalanine (DPA) were well separated by chiral HPLC and NMR spectroscopy on the chiral stationary phase (CSP) derived from (18-crown-6)-2,3,11,12-tetracarboxylic acid (18-C-6-TA). The chromatographic parameters such as separation factors and retention times were greatly influenced by the mobile phase conditions. The (+)-18-C-6-TA used in the CSP was also employed as a chiral solvating agent for the enantiodiscrimination of the DPA enantiomers by NMR spectroscopy. The proton of the DPA analyte showing the chemical shift nonequivalences was used in determining the enantiomeric composition of the analyte.