Complexes with ambidentate ligands derived from pyridine and pyrimidine-Part 2. Platinum(II) complexes

Summary Seven Pt complexes, prepared from thio-, sulphinyl, and carbonyl derivatives of pyridine and pyrimidine, were studied and compared with the analogous nickel complexes. Only when the ligand was an anionic thiolate did Pt form N, S-bonded heterocycles; in all other cases bonding occurred solely through nitrogen, in marked contrast with the Ni systems.     

Intramolecular Cyclization of Alicyclic 1,5-Di- and 1,3,5-Triketones

On a series of 44 alicyclic 1,5-di- and 1,3,5-triketones was studied the influence of various structural factors (size of the 5-7-membered ring, positions of the substituents) on the capability for intramolecular aldol condensation and on its direction. The most prone to this reaction are compounds possessing a 6-membered cycle and a substituent in the -methylene bridge. The substituent in -position to one of the carbonyl groups can affect the reaction in two ways depending on the degree of shielding of this position.     

1′-Acetylferrocene amino acid esters and amides. A simple model for parallel β-helical peptides

In this study we present a synthesis and conformational analysis of 1′-acetylferrocene amino acid derivatives of type Ac–Fn–CO–AA–Y (Fn=ferrocene-1,1-diyl; AA=Gly, Ala or Val; Y=OMe or NHMe) as a simple model for parallel β-helical peptides. Derivatives with only one amino acid adopt a reduced number of total conformations and allow a more exact analysis of intramolecular hydrogen bonds (IHB) close to the ferrocene unit. Conformational analysis of these bioconjugates was performed by a combination of spectroscopic techniques (IR, NMR and CD) and corroborated by solution-phase DFT calculations. The investigation of ester conjugates 1–3 indicates the coexistence of non-bonded (an open forms) and hydrogen bonded NH_a group forming a 7-membered ring (γ-turn). The amide derivatives 4–6 with an additional NH_b hydrogen bond donor are mostly constituted of conformers with a 10-membered ring (β-turn) as a single IHB pattern or the β-turn accompanied by a 7-membered ring (γ-turn) containing NH_a group. The exchange of the amino acid side-chain does not significantly affect the conformational properties and IHB pattern of the studied conjugates 1–6.     

A Bridged High-Spin Complex Bis-[Ni(II)( rac-5,5,7,12,12,14-hexamethyl- 1,4,8,11-tetraazacyclotetradecane)]-2,5-pyridinedicarboxylate Diperchlorate Monohydrate

A bridged high-spin complex,bis-[Ni(II)(rac-5,5,7,l2,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)]-2,5-pyridinedicarboxylate diperchlorate monohydrate has been obtained by reaction of [Ni(II)(rac-5,5,7, 12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)](ClO₄)₂ and 2,5-pyridinedicarboxylic acid in aqueousalkaline (NH₄OH) medium. C₃₉H₇₇Cl₂N₉Ni₂O₁₃, chemical formula weight 1068.42, orthorhombic, P2₁2₁2₁, a = 11 .423(3) Å,b = 14.770(6) Å, c = 31.608(7) Å, = = =90.00°, V = 5333(3) ų, Z = 4, D_calc = 1.331 g cm^-3, _calc = 0.869 mm^-1, F(000) = 2272, T = 293(2), R = 0.0870 for 2686 observed reflections [I > 2(I)]. The complexincludes two folded [Ni(rac- Me₆[14]aneN₄)]²⁺ units havingopposite diastereomeric configuration. They are bridged through a dianion of2,5-pyridinedicarboxylic acid, with one Ni-atom coordinated to the O-atom ofthe 2-carboxylic group and the pyridine N-atom (forming a 5-membered chelatering), and with the second Ni-atom coordinated to both O-atoms of the 5-carboxylic group (forming a 4-membered chelate ring). Hydrogen bonding involving macrocyclic NH groups, both 2- and 5-carboxylic groups, perchlorate anions and water molecules gives rise to the formation of an infinite supramolecular network in the title compound's crystals.     

Possible conformations and relative stability of the 7-membered ring in 1α,5β,6,7α(H)-and 1β,5α,6,7α(H)-guai-11(13)-en-6,12-olides

Stereoisomers of 1,5,6,7(H)- and 1,5,6,7(H)-guai-11(13)-en-6,12-olides are calculated using molecular mechanics. The possibility of forming various conformations in the 7-membered ring is examined as a function of the fusion to the 5-membered C-ring. The effect of the methyl orientation on the conformation of the 7-membered ring and the relative stability of the conformers are discussed.Insitute of Phytochemistry, Karaganda, fax (3212)-43-37-73. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 54–56, January–February, 2000.     

Synthesis of [13]-membered macrocyclic stevastelins via a transesterification reaction as the key step: total synthesis of stevastelin C3

A new synthesis of stevastelin C3 (3), a [13]-membered ring component of the stevastelin family, whose structure was recently revised, is reported. Initially, a macrolactonization approach was attempted to generate the [13]-membered macrolactone but this met with failure, so a translactonization reaction was tried to obtain the targeted stevastelin C3 (3) from the corresponding [15]-membered ring counterpart. Unfortunately, this strategy did not prove successful, and, consequently, we opted to undertake a transesterification reaction from 23, as a means to accommodate the requisite aminoacid moiety at the correct position, to obtain 24. From 24, and through intermediates 25-28, the acyclic precursor of the [13]-membered ring macrolactone, compound 30, was efficiently prepared. By utilizing the synthetic course developed by Chida, we took 30 forward and completed the total synthesis of stevastelin C3 (3).     

1,4,5-Thiadiazepines—II : A novel ring contraction giving 1,4-thiazine derivatives

Cyclization of methyl (phenacylsulphonyl)acetate (3a) and methyl 2-(phenacylsulphonyl)-propionate (3b) with hydrazine gave 6-phenyl-2,3,4,7-tetrahydro-1,4,5-thiadiazepin-3-one 1,1-dioxide (4a) and its 2-methyl derivative (4b), respectively. The new thiadiazepines, unlike previously described derivatives, did not undergo desulphonylation when heated in various solvents. Brief reflux of 4a in acetic anhydride gave the O-acetyl derivative (6), while prolonged reflux resulted in extrusion of one nitrogen atom from the 7-membered ring. The mechanism of the ring contraction is discussed in terms of a bicyclic diaziridine intermediate (13).     

Effects of pH and Dye Concentration on the Optical and Structural Properties of Coumarin-4 Dye-Doped SiO2-PDMS Xerogels

Optical and structural properties of coumarin-4 dye-doped SiO₂-PDMS xerogels synthesized by acid catalyzed (one-step) and acid-base catalyzed (two-step) sol-gel routes with varying pH (0.6 to 7) and dye content ( 5 × 10^–4 to 5 × 10^–2 mole) are reported. Spectroscopic methods such as photo-luminescence, FT-IR and FT-Raman were used for characterizations. The acid catalyzed xerogels prepared with pH < 2.5 exhibited two fluorescence peaks, I at 390 nm and II at 480 nm. The acid-base catalyzed xerogels synthesized with pH < 2.5 also exhibited two peaks, I at 400 nm and II at 475 nm. Peak II was not observed for the samples with pH 2.5. This phenomenon was attributed to the existence of pH dependent different forms of coumarin-4 molecule. The concentration-quenching phenomenon was observed for the acid catalyzed xerogels prepared with different dye concentration. TheFT-IR spectra indicated the existence of hydrogen bonds between the carbonyl groups of dye molecules and the silanol groups of gel matrix. The hydrogen bonding was the highest for the samples with the extremity pH, 0.6 and 7, resulting in the highest dye/gel matrix interactions, hence, the highest fluorescence peaks. The Raman studies indicated that the samples prepared with pH < 2.5 possessed relatively more number of 3-membered siloxane rings than 4-membered siloxane rings. The ring statistics was reversed for the samples with pH > 2.5. The number of silanol groups was higher for the samples with pH > 2.5.     

Synthesis and reactivity of 10-Alkylphenotellurazines

The reaction of N-alkyl-2,2-dilithium diphenylamines with tellurium diiodide yields derivatives of a new heterocyclic system, phenotellurazine. 10-Alkyl-phenotellurazines readily form derivatives containing tetra- and tricoordinated tellurium, form complexes with metal salts and rhodium(I) carbonyl chloride, and by bromination and nitration give 3,7-dibromo- or 3-nitro-, 3,7-dinitro, and 1,3, 7,9-tetranitro derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 757–768, June, 1985.     

Synthesis and thermal decomposition of cobalt-containing oligosilanes

Oligo(phenylcobaltcarbonylsilane) was prepared from oligo(phenylsilane) and dicobalt octacarbonyl. The reaction proceeds with elimination of H₂ and CO and insertion of cobalt carbonyl fragments into the silicone backbone of oligosilane. Oligosilane containing cobalt carbonyl groups in side organic substituents was obtained from oligolmethyl(phenylethynyl)Isilane and CO₂(CO)₈. The reaction of 1,2-bis(phenylethyny1)tetramethyldisilane with Co₂(CO)₈ proceeds with the sequential attachment of cobalt carbonyl fragments to ethynyl groups to form disilane derivatives [²-CCPhCo₂(CO)₆] Thermal decomposition of cobalt-containing oligosilanes affords a mixture of paramagnets and ferromagnets.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2561–2567, October, 1996.     

Synthesis and conformational aspects of 20- and 40-membered macrocyclic mono and dinuclear uranyl complexes incorporating salen and (R)-BINOL units

20- and 40-membered macrocyclic mono and dinuclear uranyl complexes 11-13 incorporating salen and (R)-BINOL units have been designed and synthesized starting from 4-tert-butylphenol in eight steps. NMR measurements (COSY, NOESY/EXSY) indicate that such complexes in solution are involved in conformational equilibria, which for the 20-membered derivatives are observable already at room temperature (k₁=300 s⁻¹ at 300 K) and which are probably related to a flipping motion of salicylaldehyde units. T-ROESY experiments suggest that in solution, the dinuclear complexes do not assume structures wrapped around the metal ions.     

Ugi products containing boronate esters

The Ugi reaction with formylphenylboronic acid derivatives as the carbonyl component proceeds to give the corresponding boron-containing dipeptide derivatives (Ugi products) in good yields.      

Application of the method of molecular orbitals to investigating the effects of conjugation between phenyl and 5-membered N-heteroatom rings

Using a Hückel approach in conjunction with the LCAO MO method, calculations are made of -electron configurations for a number of N- and C-phenyl derivatives of 5-membered nitrogen heterocyclic rings. Using these results, interaction effects between phenyl and heterocyclic ring systems are considered, as well as UV spectra, dipole moments, and reactivities of the compounds investigated.     

Investigation of nitrogen- and sulfur-containing heterocycles. 39. Reactions of 2-mercapto-3-ureido- and 2-mercapto-3-aminopyridines with β-halo carbonyl compounds. Synthesis of 6-oxo derivatives of pyrido[2,3-b][1,5]thiazepines

The reaction of 2-mercapto-3-ureido- and 2-mercapto-3-aminopyridines with -halo derivatives of carbonyl compounds (ketones, acids, and aldehydes) and with acrylonitrile proceeds not only via the mercapto group but also via the amino group, as a result of which S--keto (carboxy, cyano) alkyl, N,S-bis(-ketoalkyl), and N,S-diacyl derivatives of pyridine are formed. The action of acids, alkalis, and dehydrating agents on 2-S--keto (carboxy, cyano) ethyl-3-aminoureidopyridines was studied. A method for the preparation of derivatives of a new heterocyclic system, viz., 6-oxopyrido [2,3-b] [1,5] thiazepine, by the reaction of 2-mercapto-3-aminopyridines with -bromopropionic acid and subsequent treatment of 2-(-car-boxyethyl) thio-8-aminopyridines with dicyclohexylcarbodiimide was developed.See [5] for Communication 38.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 634–639, May, 1981.     

Synthesis of 4,5-dihydrofuran derivatives. Stereochemical study of the reactions of 1,3-alkadienes with β-dicarbonyl compounds

4,5-Dihydrofuran derivatives were obtained by the reaction of cis- and trans-1,3-alkadienes with carbonyl compounds in the presence of the manganese (III) acetate/copper (II) acetate oxidizing system. It was observed that in the case of cis-1,3-alkadienes, in contrast to trans-1,3-alkadienes, inversion of the cis double bond, the degree of which depends on the structures of the unsaturated and carbonyl components of the reaction, occurs. It was shown that the reaction of cis-1,3-dodecadiene with diethyl malonate leads to the corresponding 1,4-addition product.Communic,ation 119 from the series Reactions of unsaturated compounds. See [1] for Communication 118.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 308–314, March, 1985.     

Crystal and solution structures of di-n-butyltin(IV) complexes of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol and benzoic acid derivatives: En route to elegant self-assembly via modulation of the tin coordination geometry

Reactions of ⁿBu₂SnCl(L¹) (1), where L¹ = acid residue of 5-[(E)-2-(4-methoxyphenyl)-1-diazenyl]quinolin-8-ol, with various substituted benzoic acids in refluxing toluene, in the presence of triethylamine, yielded dimeric mixed ligand di-n-butyltin(IV) complexes of composition [ⁿBu₂Sn(L¹)(L^2-6)]₂ where L² = benzene carboxylate (2), L³ = 2-[(E)-2-(2-hydroxy-5-methylphenyl)-1-diazenyl]benzoate (3), L⁴ = 5-[(E)-2-(4-methylphenyl)-1-diazenyl]-2-hydroxybenzoate (4), L⁵ = 2-{(E)-4-hydroxy-3-[(E)-4-chlorophenyliminomethyl]-phenyldiazenyl}benzoate (5) and L⁶ = 2-[(E)-(3-formyl-4-hydroxyphenyl)-diazenyl]benzoate (6). All complexes (1-6) have been characterized by elemental analyses, IR, ¹H, ¹³C and ¹¹⁷Sn NMR and ¹¹⁹Sn Mössbauer spectroscopy and their structures were determined by X-ray crystallography, complemented by ¹¹⁷Sn CP-MAS NMR spectroscopy studies in the solid state. The crystal structure of 1 reveals a distorted trigonal bipyramidal coordination geometry around the Sn-atom where the Cl- and N-atoms of ligand L¹ occupy the axial positions. In complexes 2-5, the molecules are centrosymmetric dimers in which the Sn-atoms are connected by asymmetric μ-O bridges through the quinoline O-atom to give an Sn₂O₂ core. The differences in the Sn-O bond lengths within the bridge range from 0.28 to 0.48 Å, with the longer of the Sn-O distances being in the range 2.56-2.68 Å and the most symmetrical bridge being in 5. The carboxylate group is almost symmetrically bidentate coordinated to the tin atom in 5 (Sn-O distances of 2.327(2) and 2.441(2) Å), unlike the other complexes in which the distance of the carboxylate carbonyl O-atom from the tin atom is in the range 2.92-3.03 Å. The structure of 5 displays a more regular pentagonal bipyramidal coordination geometry about each tin atom than in 2-4. In contrast, the centrosymmetric dimeric structure of 6 involves asymmetric carboxylate bridges, resulting in a different Sn₂C₂O₄ motif. The Sn-O bond lengths in the bridge differ by about 0.6 Å, with the longer distance involving the carboxylate carbonyl O-atom (2.683(2) and 2.798(2) Å for two molecules in the asymmetric unit). The carboxylate carbonyl O-atom has a second, even longer intramolecular contact to the Sn-atom to which the carboxylate group is primarily coordinated, with these Sn?O distances being as high as 3.085(2) and 2.898(2) Å. If the secondary interactions are considered, all the di-n-butyltin(IV) complexes (2-6) display a distorted pentagonal bipyramidal arrangement about each tin atom in which the n-butyl groups occupy the axial positions.     

Metal Complexes with Macrocyclic Ligands. Part XXVII. Cu2+-promoted hydrolysis of carboxylic- and phosphonic-acid esters in the side chain of tetraazamacrocycles

The X-ray structures of the Cu²⁺ complexes of 1,4,8,11-tetraazacyclotetradecane derivatives with an ethylpro-pionate and diethylphosphonate group, 5 and 6 , respectively, indicate that the metal ion is pentacoordinated by the four N-atoms of the macrocycle and one O-atom. In the case of 5 , it is the carbonyl O-atom of the carboxylate group, whereas for 6 it is the phosphonyl O-atom of the phosphonate group. The hydrolysis kinetics of the functional group in the Cu²⁺ complexes with the 1,4,8,11-tetraazacyclotetradecanes 3 – 6 have been measured by pH-stat and stopped-flow techniques. The rate law for the hydrolysis of the carboxylates 3 – 5 is proportional to the complex concentration and to [OH^?] up to pH 13, whereas that of the phosphonate 6 is proportional to [OH^?] up to pH 11.5, becoming independent of [OH^?] at pH > 11.5. The mechanisms of these two reactions are discussed, considering the possibility of an intra- or an intermolecular OH^? attack and the results of the X-ray structure analyses.     

Oxidation of S and SO by O2 in high-temperature pyrolysis and photolysis reaction systems

The reaction of S atoms with O₂ was studied behind reflected shock waves applying atomic resonance absorption spectroscopy (ARAS) for concentration measurements of S and O atoms. S atoms were generated either by laser-flash photolysis (LFP) of CS₂ or by the high-temperature pyrolysis of COS, respectively. The concentrations of O₂ in the mixtures ranged between 50 ppm and 400 ppm, and those of the S precursors, CS₂ and COS, between 5 and 25 ppm. The rate coefficient of the reaction was determined from the observed decay of the S absorption signals for temperatures 1220 K ? T ? 3460 K. The measured O-atom concentration profiles in COS/O₂/Ar reaction systems were evaluated, using simplified kinetic mechanism, to verify the given rate coefficient k₅. In experiments with the highest value of the [O₂]/[COS] ratio the measured O-atom concentrations were found to be sensitive to the reaction: The fitting of the calculated O-atom profiles to the measured ones results in mean value of: which is to be valid for the temperature range 2570 K ? T ? 2980 K. A first-order analysis of the observed S absorption decay in LFP shock wave experiments on CS₂/Ar gas mixtures resulted in a rate coefficient of the background reaction (R4): for temperatures 1260 K ? T ? 1820 K. © 1995 John Wiley & Sons, Inc.     

N–H⋯X interactions stabilize intra-residue C5 hydrogen bonded conformations in heterocyclic α-amino acid derivatives

Nature makes extensive and elaborate use of hydrogen bonding to assemble and stabilize biomolecular structures. The shapes of peptides and proteins rely significantly on N–H⋯O C interactions, which are the linchpins of turns, sheets and helices. The C5 H-bond, in which a single residue provides both donor and acceptor, is generally considered too weak to force the backbone to adopt extended structures. Exploiting the synergy between gas phase (experimental and quantum chemistry) and solution spectroscopies to decipher IR spectroscopic data, this work demonstrates that the extended C5-based conformation in 4-membered ring heterocyclic α-amino acid derivatives is significantly stabilized by the formation of an N–H⋯X H-bond. In this synergic system the strength of the C5 interaction remains constant while the N–H⋯X H-bond strength, and thereby the support provided by it, varies with the heteroatom.

In 4-membered ring heterocyclic α-amino acid derivatives, extended conformations based on intraresidue C5 H-bonds can be stabilized by N–H⋯X H-bonds, making the combined C5–C6γ structures prominent in both gas phase and in weakly polar solutions.     

peri-Naphthylenediamines. 36. 5,6-Bis(dimethylamino)acenaphthylene in [4+2] cycloaddition reactions. Synthesis and characteristic features of protonation of “proton sponges” with the 8,9-diazafluoranthene structure

5,6-Bis(dimethylamino)acenaphthylene is readily involved in [4+2] cycloaddition reactions with symm-tetrazine derivatives to form new proton sponges with the diazafluoranthene skeleton. Under analogous condition, 1,8-bis(dimethylamino)-4-vinylnaphthalene gave 4-pyridazinyl derivatives. The relative reactivities of 5,6-bis(dimethylamino)acenaphthylene, 1,8-bis(dimethylamino)-4-vinylnaphthalene, 5-dimethylaminoacenaphthylene, and acenaphthylene in the reactions with 3,6-diphenyl-symm-tetrazine are in a ratio of 32 : 17 : 14 : 1. The site of protonation of 3,4-bis(dimethylamino)-7,10-diphenyl-8,9-diazafluoranthene is controlled by the basicity of the solvent. The reaction in acetonitrile afforded the cation stabilized by an intramolecular hydrogen bond, whereas the reaction in dimethyl sulfoxide gave rise to the resonance-stabilized cation. 6,7-Bis(dimethylamino)phenalen-1-one was protonated only at the carbonyl group.