Mono-, di-, and tetra-aurated derivatives of barbituric acid,including a new type of polynuclear gold compound. Crystal structure of 1,3-bis(triphenylphosphinegold)-5,5-diethylbarbituric acid

Reaction of barbituric acid (2,4,6-pyrimidinetrione) or its derivatives with LAuCl (L = triphenylphosphine) gave 3-LAu-5,5-diethyl-, 1,3-(L'Au)₂-5,5-diethyl- (L′ = L or L′ = Cy₃P), 1,3-dimethyl-5,5-bis(LAu)-, or 1,3,5,5-tetrakis-(LAu)barbituric acid, which were characterized as N-, N,N′-, C,C′-, or N,N′,C,C-gold derivative,s respectively, by IR, ¹H, ¹³C and ³¹P NMR spectroscopy. In the case of 1,3-(LM)(L″M)-5,5-diethylbarbituric acid compounds with M = gold and L″ either Cy₃P, Ph₃As, or (4-tolyl)₃P, or ML = ML″ = HgMe were prepared. An X-ray diffraction study of 1,3-(LAu)₂-5,5-Et₂-pyrimidin-2,4,6-trione · 3C₆H₆ revealed that (a) the heterocyclic ring is planar, (b) there is no inter- or intra-molecular Au ⋯ Au interaction, and (c) the coordination around each gold atom is approximately linear (PAuN 178.3(4)°, with AuN 2.022(12) and AuP 2.233(5) Å. The molecular parameters are compared with those for barbituric acid and other barbiturates.     

Ab initio study of C4H3 potential energy surface and reaction of ground‐state carbon atom with propargyl radical

The potential energy surface for the reaction of the ground‐state carbon atom [C(³P_j)] with the propargyl radical [HCCCH₂(X²B₁)] is investigated using the G2M(RCC,MP2) method. Numerous local minima and transition states for various isomerization and dissociation pathways of doublet C₄H₃ are studied. The results show that C(³P_j) attacks the π system of the propargyl radical at the acetylenic carbon atom and yields the n‐C₄H₃(²A′) isomer i3 after an 1,2‐H atom shift. This intermediate either splits a hydrogen atom and produces singlet diacetylene, [HCCCCH ( p1 )+H] or undergoes (to a minor amount) a 1,2‐H migration to i‐C₄H₃(²A′) i5 , which in turn dissociates to p1 plus an H atom. Alternatively, atomic carbon adds to the triple C?C bond of the propargyl radical to form a three‐member ring C₄H₃ isomer i1 , which ring opens to i3 . Diacetylene is concluded to be a nearly exclusive product of the C(³P_j)+HCCCH₂ reaction. At the internal energy of 10.0 kcal/mol above the reactant level, Rice–Ramsperger–Kassel–Marcus calculations show about 91.7% of HCCCCH comes from fragmentation of i3 and 8.3% from i5 . The other possible minor channels are identified as HCCCC+H₂ and C₂H+HCCH. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1522–1535, 2001     

Reactions of 2,3-Dichloro- and 2,3,5-Trichloro-4,4-ethylenedioxy-2-cyclopentenones with Some O-, S-, and N-Nucleophiles

2,3-Dichloro- and 2,3,5-trichloro-4,4-ethylenedioxy-2-cyclopentenones react with allyl and benzyl alcoholates and thiolates and benzylamine to give products resulting from Ad_NE substitution of the 3-chlorine atom, [1,3]-sigmatropic rearrangement, and cleavage of the C¹-C² bond.     

Acid-Catalyzed [3,3]-Sigmatropic Rearrangements of N-Propargylanilines

The acid-catalyzed rearrangement of N-(1′,1′-dimethylprop-2′-ynyl)-, N-(1′-methylprop-2′-ynyl)-, and N-(1′-arylprop-2′-ynyl)-2,6-, 2,4,6-, 2,3,5,6-, and 2,3,4,5,6-substituted anilines in mixtures of 1N aqueous H₂SO₄ and ROH such as EtOH, PrOH, BuOH etc., or in CDCl₃ or CCl₄ in the presence of 4 to 9 mol-equiv. trifluoroacetic acid (TFA)has been investigated (cf. Scheme 12-25 and Tables 6 and 7). The rearrangement of N-(3′-X-1′,1′-dimethyl-prop-2′-ynyl)-2,6- and 2,4,6-trimethylanilines (X = Cl, Br, I) in CDCl₃/TFA occurs already at 20° with τ_1/2 of ca. 1 to 5 h to yield the corresponding 6-(1-X-3′-methylbuta-1,2′-dienyl)-2,6-dimethyl- or 2,4,6-trimethylcyclohexa-2,4-dien-1-iminium ions (cf. Scheme 13 and Footnotes 26 and 34) When the 4 position is not substituted, a consecutive [3,3]-sigmatropic rearrangement takes place to yield 2,6-dimethyl-4-(3′-X-1′,1′-dimethylprop-2′-ynyl)anilines (cf. Footnotes 26 and 34). A comparable behavior is exhibited by N-(3′-chloro-1′-phenylprop-2′-ynyl)-2,6-dimethylaniline ( 45 ., cf. Table 7). The acid-catalyzed rearrangement of the anilines with a Cl substituent at C(3′) in 1N aqueous H₂SO₄/ROH at 85-95°, in addition, leads to the formation of 7-chlorotricyclo[3.2.1.0^2,7]oct-3-en-8-ones as the result of an intramolecular Diels-Alder reaction of the primarily formed iminium ions followed by hydrolysis of the iminium function (or vice versa; cf. Schemes 13,23, and 25 as well as Table 7). When there is no X substituent at C(1′) of the iminium-ion intermediate, a [1,2]-sigmatropic shift of the allenyl moiety at C(6) occurs in competition to the [3,3]-sigmatropic rearrangement to yield the corresponding 3-allenyl-substituted anilines (cf. Schemes 12,14–18, and 20 as well as Tables 6 and 7). The rearrangement of (?)?(S)-N-(1′-phenylprop-2′-ynyl)-2,6-dimethylaniline ((?)- 38 ; cf. Table 7) in a mixture of 1N H₂SO₄/PrOH at 86° leads to the formation of (?)-(R)-3-(3′-phenylpropa-1′,2′-dienyl)-2,6-dimethylaniline ((?)- 91 ), (+)-(E)- and (?)-(Z)-6-benzylidene-1,5-dimethyltricyclo[3.2.1.0^2′7]oct-3-en-8-one ((+)-(E)- and (?)-(Z)- 92 , respectively), and (?)-(S)-2,6-dimethyl-4-( 1′-phenylprop-2′-ynyl)aniline((?)- 93 ). Recovered starting material (10%) showed a loss of 18% of its original optical purity. On the other hand, (+)-(E)- and (?)-(Z)- 92 showed the same optical purity as (minus;)- 38 , as expected for intramolecular concerted processes. The CD of (+)-(E)- and (?)-(Z)- 92 clearly showed that their tricyclic skeletons possess enantiomorphic structures (cf. Fig. 1). Similar results were obtained from the acid-catalyzed rearrangement of (?)-(S)-N-(3′-chloro-1′phenylprop-2′-ynyl)-2,6-dimethylaniline ((?)- 45 ; cf. Table 7). The recovered starting material exhibited in this case a loss of 48% of its original optical purity, showing that the Cl substituent favors the heterolytic cleavage of the N–C(1′) bond in (?)- 45. A still higher degree (78%) of loss of optical activity of the starting aniline was observed in the acid-catalyzed rearrangement of (?)-(S)-2,6-dimethyl-N-[1′-(p-tolyl)prop-2′-ynyl]aniline ((?)- 42 ; cf. Scheme 25). N-[1′-(p-anisyl)prop-2-ynyl]-2,4,6-trimethylaniline( 43 ; cf. Scheme 25) underwent no acid-catalyzed [3,3]-sigmatropic rearrangement at all. The acid-catalyzed rearrangement of N-(1′,1′-dimethylprop-2′-ynyl)aniline ( 25 ; cf. Scheme 10) in 1N H₂SO₄/BuOH at 100° led to no product formation due to the sensitivity of the expected product 53 against the reaction conditions. On the other hand, the acid-catalyzed rearrangement of the corresponding 3′-Cl derivative at 130° in aqueous H₂SO₄ in ethylene glycol led to the formation of 1,2,3,4-tetrahydro-2,2-dimethylquinolin-4-on ( 54 ; cf. Scheme 10), the hydrolysis product of the expected 4-chloro-1,2-dihydro-2,2-dimethylquinoline ( 56 ). Similarly, the acid-catalyzed rearrangement of N-(3′-bromo-1′-methylprop-2′-ynyl)-2,6-diisopropylaniline ( 37 ; cf. Scheme 21) yielded, by loss of one i-Pr group, 1,2,3,4-tetrahydro-8-isopropyl-2-methylquinolin-4-one ( 59 ).     

Poly[cadmium(II)-μ-4,4′-oxydianiline-N:N′-di-μ-thiocyanato-N:S]

The title polymeric complex, [Cd(SCN)₂(C₁₂H₁₂N₂O)], exhibits a three-dimensional framework in which each Cd^II atom is bridged by two η-1,3-(SCN)⁻ groups, forming a double-stranded chain. The unique Cd^II atom lies on an inversion centre and the coordination sphere is completed by two terminal N atoms from two different 4,4′-oxy­dianiline (4,4′-Oda) ligands, furnishing a CdS₂N₄ octahedral geometry. Adjacent polymeric double-stranded chains are linked via the 4,4′-Oda ligands, which lie across twofold rotation axes.     

DFT studies on key intermediates in thiamin catalysis

The diphosphate ester (ThDP) of thiamin (vitamin B₁) is an important cofactor of enzymes within the carbohydrate metabolism. From experiments of site‐specific variants and nuclear magnetic resonance (NMR) studies, it is known that the protonation of the N1′ atom is a significant step in the coenzyme activation by the enzymatic environment. Therefore, we have performed density functional theory (DFT) calculations on the B3LYP/6‐31G* level of N1′H and N1′CH₃ thiamin as model systems to study the protonation and methylation effect on the structure and the electronic properties of the 4′‐amino group. The relaxed rotational barriers related to the C4′‐4′N bond are correlated with findings of ¹H NMR studies and proton/deuterium exchange experiments. Moreover, the effect of N1′ protonation was studied in more detail on the hydroxyethyl‐thiamin carbanion (HETh^?), a key intermediate during catalysis of some ThDP‐dependent enzymes. The relaxed rotational barriers related to the C2? C2α bond and the reaction coordinates of the proton transfer 4′N? H→C2α of HETh^? and N1′H‐HETh^? show that they are significantly determined by the protonation at N1′ of HETh^?. The influence of the apoenzyme environment on the active coenzyme conformation is modeled in a very simple way. The characteristic torsion angles Φ_T and Φ_P are considered to be restricted in terms of their values in the corresponding enzyme as well as free optimization parameters. Frequency calculations were performed to characterize the minima and transition state structures, respectively. The applicability of the DFT method was checked by comparing calculations on the MP2‐HF‐SCF/6‐31G* level. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Reaction of N‐Heterocyclic Silylenes with Thioketone: Formation of Silicon–Sulfur Three (Si‐C‐S)‐ and Five (Si‐C‐C‐C‐S)‐Membered Ring Systems

Three‐ and five‐membered rings that bear the (Si‐C‐S ) and (Si‐C‐C‐C‐S ) unit have been synthesized by the reactions of L SiCl ( 1 ; L =PhC(NtBu)₂) and L′ Si ( 2 ; L′ =CH{(C?CH₂)(CMe)(2,6‐iPr₂C₆H₃N)₂}) with the thioketone 4,4′‐bis(dimethylamino)thiobenzophenone. Treatment of 4,4′‐bis(dimethylamino)thiobenzophenone with L SiCl at room temperature furnished the [1+2]‐cycloaddition product silathiacyclopropane 3 . However, reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si at low temperature afforded a [1+4]‐cycloaddition to yield the five‐membered ring product 4 . Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single‐crystal X‐ray structural analysis. The room‐temperature reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′ Si resulted in products 4 and 5 , in which 4 is the dearomatized product and 5 is formed under the 1,3‐migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the C? S unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations.     

High‐resolution 15N solid‐state NMR investigations on borazine‐based precursors

Reference compounds based on borazine units and polyborylborazines have been characterized by ¹⁵N solid‐state NMR. The various nitrogen sites (B₃N, B₂NH, B₂NX (X = H, Me, ⁱPr), BN(H)X and BNX₂ (X = Me, ⁱPr) have been discriminated according to their cross‐polarization behaviour and chemical shift values, which range from ?265 to ?350 ppm. This has permitted the elucidation of the polymerization mechanism associated with the polycondensation of two borazine‐based derivatives. In particular, this technique appears to be a powerful investigation tool for finding whether the B₃N₃ rings are linked through three‐atom N? B? N aminoboryl bridges or connected by direct B? N bonds. Copyright © 2004 John Wiley & Sons, Ltd.     

Zur Kenntnis der Indolreaktion nach Fischer. II. Thermische und säurekatalysierte Indolisierung von 1′-Alkenyl-2′-methyl-2′-phenylacetohydraziden

On the Fischer-Indole Reaction. II. Thermal and Acid Catalysed Indolization of 1′-Alkenyl-2′-methyl-2′-phenylacetohydrazides Seven different 1′-alkenyl-2′-methyl-2′-phenylacetohydrazides, 6a-g , have been prepared by treatment of the methylphenylhydrazones 7 of appropriate ketones and aldehydes with acetyl chloride in pyridine. At 170° 6a-g are transformed into the N-methylindoles 3a-g and acetamide in moderate yield. N-Methylaniline is the other major reaction product indicating that homolytic cleavage of the weak N, N-bond in 6 is a major primary reaction step. It is likely but not proven that the N-methylindoles 3 are formed in a reaction sequence initiated by an uncatalysed concerted [3, 3]-sigmatropic rearrangement. Upon treatment of 6 with 0.5N dichloroacetic acid in anhydrous acetonitrile at room temperature a quantitative conversion to 3 is observed, interpreted as proceeding by a charge induced [3, 3]-sigmatropic rearrangement of protonated 6 in the rate determining step. The ketone derivatives 6a-e (R¹ = alkyl) react 40-1000 times faster with acid than the aldehyde derivatives 6f and 6g (R¹ = H). This is rationalized as a consequence of the increased basicity of 6a-e relative to 6f and 6g caused by a steric effect.     

Unkatalysierte sigmatrope 1,5-Wanderung von Acylgruppen bei der Thermolyse von 5-Acyl-5-methyl-1,3-cyclohexadienen

Uncatalyzed Sigmatropic 1,5-Shift of Acyl Groups in the Thermolysis of 5-Acyl-5-methyl-1,3-cyclohexadienes Four different 5-acyl-5-methyl-1,3-cyclohexadienes 1a–d (R = COOCH₃, COCH₃, COC₆H₅, CHO) have been shown to yield mixtures of 1,3-disubstituted cyclohexadienes 2–7 and 1,3-disubstituted aromatic product 8 upon thermolysis at 150–300° in solution and at 350–500° in the gas phase in a flow system. Two reaction pathways (A and B in Scheme 2) are considered for the rearrangement of the C-Skeleton. For the ester 1a ¹³C-isotopic substitution shows that products arise to 75–86% through a 1,5-sigmatropic shift of the methoxycarbonyl group ( A in Scheme 2) and to 14–25% through a sequence of reaction steps involving a 1,7-H-shift reaction in an acyclic intermediate ( B in Scheme 2). For the more reactive compounds 1b–d isomerization is assumed to follow the 1,5-sigmatropic pathway exclusively ( A in Scheme 2). A kinetic study yields the following sequence for the migration tendency of acyl groups toward sigmatropic 1,5-shift: COOCH₃ < COCH₃ < COC₆H₅ < CHO.     

Dichloro(2,2′‐diamino‐4,4′‐bi‐1,3‐thiazole‐N3,N3′)copper(II)

The title complex, [CuCl₂(C₆H₆N₄S₂)], has a flattened tetrahedral coordination. The Cu^II atom is located on a twofold rotation axis and is coordinated by two N atoms from a chelating 2,2′‐di­amino‐4,4′‐bi‐1,3‐thia­zole ligand and by two Cl atoms. Intramolecular hydrogen bonding exists between the amino groups of the 2,2′‐di­amino‐4,4′‐bi‐1,3‐thia­zole ligand and the Cl atoms. The intermolecular separation of 3.425 (1) Å between parallel bi­thia­zole rings suggests there is a π–π interaction between them.     

MetalAzo and metalimine compounds : III. The influence of metal basicity on the cleavage of C:H bonds by RhI and IrI

From the reaction of R′X=NR (X = N or CH) with [MCl(C₈H₁₄)_2| in the presence of CO or PR₃. σ(_N)- coordinated complexes cis-RhCl(CO)₂(R′CH=NR) and cyclometallated complexes MHCl(L′)(PR₃)₂ [′ is cyclometallated R′X=NR; R = Ph or Cy when M = Ir; R = Cy when M = Rh] were isolated.The ease of CH bond breaking by M¹ appears to be strongly dependent on the basic properties of M_I, and decreases as follows: aromatic CH > olefinic CH > aliphatic CH. On the basis of the chemical and structural information, the metallation can be explained in terms of Pearson's symmetry rules for chemical reactions.For the cyclometallated azo compounds, ν(N=N) shows resonance enhancement ion the Raman spectra, and appears to be very sensitive to the basicity of M^I in the reactant system.     

A three‐dimensional cadmium(II) coordination polymer: poly[[[μ‐4,4′‐(propane‐1,3‐diyl)dipyridine‐κ2N:N](μ‐3,3′‐thiodipropionato‐κ3O,O′:O)cadmium(II)] monohydrate]

In the title coordination polymer, {[Cd(C₆H₈O₄S)(C₁₃H₁₄N₂)]·H₂O}_n, the Cd^II atom displays a distorted octahedral coordination, formed by three carboxylate O atoms and one S atom from three different 3,3′‐thiodipropionate ligands, and two N atoms from two different 4,4′‐(propane‐1,3‐diyl)dipyridine ligands. The Cd^II centres are bridged through carboxylate O atoms of 3,3′‐thiodipropionate ligands and through N atoms of 4,4′‐(propane‐1,3‐diyl)dipyridine ligands to form two different one‐dimensional chains, which intersect to form a two‐dimensional layer. These two‐dimensional layers are linked by S atoms of 3,3′‐thiodipropionate ligands from adjacent layers to form a three‐dimensional network.     

Influence of N‐Alkyl Substituents and Counterions on the Structural and Mesomorphic Properties of Guanidinium Salts: Experiment and Quantum Chemical Calculations

A series of N‐4‐(4′‐alkoxybiphenyl)‐N′,N′,N”,N“‐tetramethylguanidinium salts was synthesized with varying alkoxy chain lengths and additional N‐alkyl substituents, each with a number of different counterions. X‐ray crystal‐structure analyses of 1b I , 1b PF₆ , 2a I , and 4a I reveal bilayer structures in the solid state and, for the 1b and 1b PF₆ salts, a hydrogen‐bond‐type connectivity between the guanidinium N‐H group and the anion is found. For the N‐alkyl homologues 2a I and 4a I the anion is still oriented close to the head group, although at a larger distance. Ion pairs are present also in solution, as demonstrated by ¹H NMR: the N‐H chemical shift shows a good linear correlation with the radius, and hence the hardness, of the anion. The intramolecular conformational flexibility of 1b I , 2b I , 3b I, and 4b I was studied by temperature‐dependent ¹H NMR spectroscopy and discrete activation barriers were determined for rotations about each of the three C? N partial double bonds of the guanidinium core. The relative heights of the individual barriers change between the N‐H and the N‐alkylguanidinium salts. A fourth barrier is observed for the rotation about the N? biphenyl bond. DFT calculations of charge densities show that the positive charge resides primarily on the central carbon atom. Rotational barriers were calculated for N′‐substituted 2‐amino‐1,3‐dimethylimidazolidinium cations as models, and are in qualitatively good agreement with the NMR data. Mesomorphic properties were studied by differential‐scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction (WAXS/SAXS). All liquid‐crystalline guanidinium salts exhibit smectic A mesophases. Clearing temperatures show a linear correlation with the anionic radius. Substitution of the N‐H group with methyl, ethyl, or propyl results in decreasing mesophase widths and a concomitant shrinkage of the layer spacings.     

13C, 15N and 29Si nuclear magnetic resonance studies of some aminosilanes and aminodisilanes

¹³C, ¹⁵N (at natural abundance) and ²⁹Si NMR data (chemical shifts and coupling constants) are reported for aminosilanes R₂R′SiNHR¹ (1), bis(silyl)amines Me₂R′SiNHSiMe₃ (2), 1,2-bis(amino)-ethanes (3), bis(amino)silanes RR′Si(NHR¹)₂ (4), 1,2-bis(amino)tetramethyldisilanes (5) and 1,1,2,2-tetrakis(amino)dimethyldisilanes (6). The δ¹⁵N values depend more on the nature of the substituents R¹(H, alkyl, aryl) at the nitrogen atom (in the same way as for other amines) than on different substituents at the silicon atom. A linear correlation between ¹J(²⁹Si¹⁵N) and ¹J(²⁹Si¹³C) is proposed for silanes in which the SiN unit is replaced by the SiCH unit. This correlation comprises all ¹J(²⁹Si¹⁵N) values for aminosilanes R_4-nSi(N)n (n = 1–4) and—most likely—also for aminodisilanes, and it predicts ¹J(²⁹Si¹⁵N)>0 if the corresponding value |¹J(²⁹Si¹³C)|>25 Hz. For the first time a two-bond coupling across Si, ²J(²⁹Si ¹⁵N) = 6.9 Hz, has been observed for 6a. In the case of 6b (R¹ = ^sBu) all resonances for the diastereomers are resolved in the ¹⁵N and ²⁹Si NMR spectra in contrast to the ¹H and ¹³C NMR spectra.     

Darstellung und eigenschaften cyclischer silylamide des berylliums. Kristall- und molekülstruktur eines dimeren diaza-disila-berylla-cyclohexans

Four novel cyclic beryllium silylamides (I–IV; R = CH₃) were obtained by reaction of BeMe₂ with the appropriate aminosilanes. In solution and in the solid state they form dimers and probably higher associated oligomers, which,

according to their ¹H NMR spectra, interconvert depending on temperature and solvent. Crystallic II dimerizes via a centrosymmetric BeNBe′N′ four-membered ring, the BeN and BeN′ distances being 1.714(3) and 1.683(3) Å. The CN and SiN bonds of the tetracoordinate N atom (1.502(3) and 1.752(3) Å) are longer than those formed by the tricoordinate N atom (1.473(3) and 1.722(2) Å); the BeN (tricoordinate N) distance is 1.550(4) Å.     

Alkene insertion reactions of nitrogen-coordinated acylpalladium(II) complexes. The crystal structure of the dicyclopentadiene insertion product [Pd(C10H12COMe)(bpy)]SO3CF3

The new acylpalladium(II) complex [PdI(COMe)(bpy)] (2b, bpy = 2,2′-bipyridyl) has been obtained by two routes; (i) by insertion of carbon monoxide into the PdC bond of [PdIMe(bpy)] (1b), and (ii) by ligand exchange from [PdI(COMe)(tmeda)] (2a, tmeda = N,N,N′,N′-tetramethylethanediamine). The cationic species obtained by reaction of 2a and 2b with AgOSO₂CF₃ both undergo alkene insertions into the PdC acyl bond that lead to remarkably stable products. The X-ray structure of the dicyclopentadiene insertion product [Pd(C₁₀H₁₂COMe)(bpy)]SO₃CF₃ (4b) shows the oxygen atom of the carbonyl group to be coordinated to the metal center (PdO = 2.026(3) Å).     

Intramolecular easily polarizable hydrogen bonds with anilides of 1-piperidine carboxylic acids

IR spectra are plotted from anilides of 1-piperidine carboxylic acids C₅H₁₀N(CH₂)_n CONHC₆H₄R in CHCl₃ and CDCl₃ solutions. In the cases of n = 1 and n = 4, weak intramolecular (NH?N) hydrogen bonds are formed. An asymmetrical energy surface occurs and the proton is present at the N of the anilide group. In the cases of n = 2 and n = 3, intramolecular proton transfer hydrogen bonds of the types N_BH?N_P ? ^?N_B?H⁺N_p are formed. In contrast to the intramolecular OH? N ? O^?1 ? H⁺N bonds with 1-piperidine carboxylic acids, these bonds to not cause IR continua but two bands: one in the region 3250–3190 and one in the region 2500–2450 cm^?1. The fact that, instead of IR continua, bands are observed is explained by the following: (1) these hydrogen bonds are relatively long; (2) they show only a narrow distribution of bond length; (3) the electrical fields at these bonds are small, since they are strongly screened.     

S-alkyl and S-alkylaryl cysteine complexes with platinum(II) and their interactions with nucleosides

The reactions of K₂PtCl₄ with the aminoacids, S-methyl-L-cysteine, S-ethyl-L-cysteine, S-benzyl-L-cysteine, S-para-nitro-benzyl-L-cysteine, S-diphenyl-methyl-L-cysteine, S-tribenzyl-L-cysteine and S-4′,4′-dimethoxy-diphenylmethyl-L-cysteine were studied in neutral or acidic aqueous solutions. Complexes of the formulae PtLCl₂, [PtL₂]Cl₂ and Pt(L-H⁺)₂, where L = aminoacid, were isolated in the solid state and their structures investigated with elemental analysis, conductivity measurements, IR, ¹H NMR and ¹³CNMR spectra. The results show that the coordination sites of Pt(II) with the amino-acids are the N and S atoms, producing two diastereoisomers around the chiral sulphur atom, which were identified in the ¹H NMR and ¹³CNMR spectra. The complexes PtLCl₂ further react with the nucleosides guanosine and inosine. The complexes [PtL(nucl)₂]Cl₂ were isolated from these reactions and studied with the same methods. They showed a PtN₇ bonding with the nucleosides and retained the N, S bondings with the aminoacids. As a result of the higher trans influence of S than N, the nucleoside molecule coordinated to the metal through N₇ and trans to S has a weaker bond strength than the other, as it is revealed from the ¹H NMR and ¹³C NMR spectra of these complexes.     

2,3‐Dihydro‐1,3‐benzothiazol‐2‐iminium monohydrogen sulfate and 2‐iminio‐2,3‐dihydro‐1,3‐benzothiazole‐6‐sulfonate: a combined structural and theoretical study

The 2‐aminobenzothiazole sulfonation intermediate 2,3‐dihydro‐1,3‐benzothiazol‐2‐iminium monohydrogen sulfate, C₇H₇N₂S⁺·HSO₄⁻, (I), and the final product 2‐iminio‐2,3‐dihydro‐1,3‐benzothiazole‐6‐sulfonate, C₇H₆N₂O₃S₂, (II), both have the endocyclic N atom protonated; compound (I) exists as an ion pair and (II) forms a zwitterion. Intermolecular N—H...O and O—H...O hydrogen bonds are seen in both structures, with bonding energy (calculated on the basis of density functional theory) ranging from 1.06 to 14.15 kcal mol⁻¹. Hydrogen bonding in (I) and (II) creates DDDD and C(8)C(9)C(9) first‐level graph sets, respectively. Face‐to‐face stacking interactions are observed in both (I) and (II), but they are extremely weak.