Bridging Nitrogen Research Articles

Magnetic and spectral studies on nickel(II) and copper(II) dithiocarbazates derived from isoniazid

Some isonicotinoyldithiocarbazate complexes of nickel(II) and copper(II), of general formulae M(IN-Dtcz)2, [M(IN-DtczH)2]Cl2, and [M(IN-DtczH-Sal)2]Cl2 (M = Ni(II), Cu(II); INDtcz = isonicotinoyldithiocarbazate; IN-DtczH = isonicotinoyldithiocarbazic acid; IN-DtczH-Sal = salicylaldehyde Schiff base of isonicotinoyldithiocarbazic acid), have been synthesized. These complexes have been investigated by elemental analyses, mass, room temperature infrared and electronic spectra, and variable temperature magnetic susceptibility measurements. The three nickel(II) dithiocarbazates and [Cu(IN-DtczH-Sal)2]Cl2 exhibit NS linkage of the ligands, while Cu(IN-Dtcz)2 and [Cu(IN-DtczH)2]Cl2 have ONS binding of the ligands. The nickel(II) dithiocarbazates have [NiN2S2] chromophore. Magnetic and solution electronic absorption spectral data reveal square-planar geometry for Ni(IN-Dtcz)2 and the existence of square-planar–tetrahedral equilibrium for [Ni(IN-DtczH)2]Cl2 and [Ni(IN-DtczH-Sal)2]Cl2. Copper(II) dithiocarbazates, namely Cu(IN-Dtcz)2, [Cu(IN-DtczH)2]Cl2, with ONS ligands having dimeric or polymeric octahedral structures, and [Cu(IN-DtczH-Sal)2]Cl2, with NS binding having dimeric square-planar structure, exhibit antiferromagnetism. Superexchange pathway involving the bridging nitrogen and sulfur of the isonicotinoyldithiocarbazate ligands rather than direct metal–metal exchange is suggested for antiferromagnetic interactions. The spin exchange parameter, −2J = 202.14 and 29.26 cm−1, has been evaluated for [Cu(IN-DtczH)2]Cl2 and [Cu(IN-DtczH-Sal)2]Cl2, respectively, while it could not be evaluated for Cu(IN-Dtcz)2 because the slope was negative due to the non-variation of its magnetic moment with temperature. The difference in antiferromagnetic behavior and inconsistency of 2J for [Cu(IN-DtczH-Sal)2]Cl2 has been attributed to different electronic and steric factors of the three ligands, that is, isonicotinoyldithiocarbazate, its acid, and salicylaldehyde Schiff-base derivative.

Novel Na–Li–SiAlPON glasses prepared by melt synthesis using AlN

Abstract Amorphous alumino–silicophosphate materials containing up to 1.70 wt.% nitrogen have been successfully prepared by aluminium nitride solution in Na–Li–Si–Al–P–O melts at 850 °C thus preventing phosphorus volatilisation. Although the solubility limit for nitrogen in these glasses was limited to 8.31 wt.%, the presence of nitrogen in the materials greatly increases their glass transition temperatures, suppresses the devitrification and has a significant effect on their melting behaviour. Comparative analysis of Raman spectra for the oxide and oxynitride glasses shows the substitution of P–O–P linkages by P N–P linkages while tri-coordinated nitrogen bridges were not detected. The attendant increase in network connectivity arising from such a substitution is responsible for the increase in glass transition temperature when nitrogen substitutes for oxygen.

Recent Developments in the [5+2] Cycloaddition

AbstractThe rapid generation of molecular complexity in a relatively easy manner has made the [5+2] cycloaddition approach a highly useful tool in the synthesis of a wide number of complex natural products and important biologically active products containing seven‐membered rings. Besides the common and highly efficient [5+2] cycloadditions of oxidopyrylium and oxidopyridinium ions with π‐systems which offer an easy access to a wide range of novel heterocyclic seven‐membered ring molecules with a oxygen or nitrogen bridge, and the less employed [5+2] photocycloadditions, the metal‐catalyzed [5+2] cycloadditions have attracted a lot of attention and have become one of the most popular ways of constructing seven‐membered ring products. All these cycloadducts can be synthetically manipulated easily toward a number of interesting molecular structures with high potential applications. Abbreviations: Ac: acetyl; Ar: aryl; BarF: tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate; BINAP: 2,2′‐bis(diphenylphosphanyl)‐1,1′‐binaphthyl; Bn: benzyl; Boc: tert‐butoxycarbonyl; Bu: butyl; Bz: benzoyl; Cbz: benzyloxycarbonyl; cod: cyclooctadiene; Cp: cyclopentadienyl; DBU: 1,8‐diazabicyclo[5.4.0]undec‐7‐ene; DCE: 1,2‐dichloroethane; de: diastereomeric excess; DFT: density functional theory; DMF: dimethylformamide; DMSO: dimethyl sulfoxide; dppb: 1,4‐bis(diphenylphosphino)butane; dppe: 1,2‐bis(diphenylphosphine)ethane; dppp: 1,3‐bis(diphenylphosphino)propane; ee: enantiomeric excess; Et: ethyl; HFIP: hexafluoroisopropyl alcohol; L: ligand; M: metal; Me: methyl; MOM: methoxymethyl; Ms: mesyl; Ph: phenyl; PMB: para‐methoxybenzoyl; Pr: propyl; Segphos: 5,5′‐bis(diphenylphosphino)‐4,4′‐bi‐1,3‐benzodioxole; TBDPS: tert‐butyldiphenylsilyl; TBS: tert‐butyldimethylsilyl; TEA: triethylamine; Tf: trifluoromethanesulfonyl; TFE: trifluoroethanol; THP: tetrahydropyran; TIPS: triisopropylsilyl; TMS: trimethylsilyl; Tol: tolyl; Tp: hydridotris(pyrazolyl)borate; Ts: 4‐toluenesulfonyl (tosyl); VCP: vinylcyclopropane.

Solvent mediated reaction of 1-methyl-1H-tetrazoline-5-thione with iodine

1-Methyl-1H-tetrazoline-5-thione (1) reacts with iodine in CHCl3 with formation of 1:1 stable σ-complex (logβ = 3.8 ± 0.1 is found by spectrophotometry). In the ethanol solution irreversible oxidation with formation of disulfide product 5,5′-dithiobis(1-methyl-1H-tetrazole) (2) is observed. The structure of (2) was determined by X-ray diffraction. Strong intermolecular interactions with shortened contacts are observed between sulfur atom of disulfide bridge and heterocyclic nitrogen of the neighboring molecule (S···N 3.0179(15) A) forming infinite supramolecular chains which are further linked with π–π stacking interaction of tetrazole rings (interplane distance is 3.1685(6) A).

Synthesis of Diverse N,O-Bridged Calix[1]arene[4]pyridine-C60 Dyads and Triads and Formation of Intramolecular Self-Inclusion Complexes

Starting from both the bridging nitrogen atom-functionalized and the upper rim-functionalized N,O-bridged calix[1]arene[4]pyridine reactants, different types of heteracalixaromatics-C(60) dyads and triads of varied spacers were expediently synthesized using mainly the click reaction as the key step. By means of various spectroscopic methods, the heteracalixaromatics-C(60) dyads and triads obtained have been shown to form intramolecular self-inclusion complexes rather than oligomers or polymers in solution because of a flexible spacer in between the heteracalixaromatic ring and C(60) moiety. The current study, coupled with previous investigations, would provide the guideline for the construction of supramolecular fullerene motifs based on molecular design of the dyads and triads.

In Search of Stable Blue Emission from Phenylene-Based Conjugated Polymers

Phenylene-based polymers are a widely studied class of blue-emitting materials for use in polymer light-emitting diodes intended for display applications. This review looks at the various types of such polymers that have been synthesised and the problems that have arisen in obtaining stable and efficient blue emission from them. The emission colour from phenylene-based polymers can be controlled by linking some or all of the phenylene units with short carbon or nitrogen bridges, and it has been found that by varying the amount and type of bridges pure blue emission can be obtained. Both aggregation of chains, and the formation of emissive defects cause instability of the emission colour and it is shown that this can be surmounted by appropriate choice of substituents and synthetic routes. In particular the formation of defects is promoted by hydrogens on the bridgeheads, and polymers with aryl substituents at the bridgeheads have been found to much more stable than those with alkyl substituents. High device efficiency can be obtained by incorporation of appropriate charge transporting substituents, which also may help with reducing problems with colour stability. It is shown that by correct design of the polymer structure and appropriate synthetic strategy it is possible to obtain efficient, stable, pure blue emission from phenylene- based polymers. Keywords: electroluminescence, light-emitting diodes

Dinuclear complex of gold(III) with 1,3-diaminopropane (HL), [Au2(HL)(L)2](ClO4)3(OH): Synthesis and crystal and molecular structures

The dinuclear gold(III) complex, [Au2(HL)(L)2](ClO4)3(OH) (I) (HL = 1,3-diaminopropane), with two amide bridges has been synthesized for the first time. According to the X-ray diffraction data, the crystal structure of complex I consists of the complex cations [Au2(HL)(L)2]4+ and anions ClO4− and OH−. The coordination sites AuN4 are insignificantly distorted squares. In the four-membered ring Au2N2, the gold atoms are bound by the bridging nitrogen atoms of the deprotonated primary amine.

Use of a Reduced Schiff-Base Ligand to Prepare Novel Chloro-Bridged Chains of Rare Cu(II) Trinuclear Complexes with Mixed Azido/Oxo and Chloro/Oxo Bridges

Two mixed bridged one-dimensional (1D) polynuclear complexes, [Cu(3)L(2)(mu(1,1)-N(3))(2)(mu-Cl)Cl](n) (1) and {[Cu(3)L(2)(mu-Cl)(3)Cl].0.46CH(3)OH}(n) (2), have been synthesized using the tridentate reduced Schiff-base ligand HL (2-[(2-dimethylamino-ethylamino)-methyl]-phenol). The complexes have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. In both complexes the basic trinuclear angular units are joined together by weak chloro bridges to form a 1D chain. The trinuclear structure of 1 is composed of two terminal square planar [Cu(L)(mu(1,1)-N(3))] units connected by a central Cu(II) atom through bridging nitrogen atoms of end-on azido ligands and the phenoxo oxygen atom of the tridentate ligand. These four coordinating atoms along with a chloride ion form a distorted trigonal bipyramidal geometry around the central Cu(II). The structure of 2 is similar; the only difference being a Cl bridge replacing the mu(1,1)-N(3) bridge in the trinuclear unit. The magnetic properties of both trinuclear complexes can be very well reproduced with a simple linear symmetrical trimer model (H = -JS(i)S(i+1)) with only one intracluster exchange coupling (J) including a weak intertrimer interaction (j) reproduced with the molecular field approximation. This model provides very satisfactory fits for both complexes in the whole temperature range with the following parameters: g = 2.136(3), J = -93.9(3) cm(-1) and zj = -0.90(3) cm(-1) (z = 2) for 1 and g = 2.073(7), J = -44.9(4) cm(-1) and zJ' = -1.26(6) cm(-1) (z = 2) for 2.

Synthesis, Structure, and Functionalization of Homo Heterocalix[2]arene[2]triazines: Versatile Conformation and Cavity Structures Regulated by the Bridging Elements

A number of homo[2] and homo[4] heterocalix[2]arene[2]triazines were synthesized through a general and good-yielding fragment coupling approach starting from cyanuric halides, aromatic and aliphatic diols, and diamines under very mild reaction conditions. While homo[2] tetraazacalix[2]arene[2]triazine gave a twisted and pinched 1,2-alternate conformer, almost all homo[2] heterocalix[2]arene[2]triazines adopted different partial cone conformations in the solid state. Homo[4] heterocalix[2]arene[2]triazines yielded more diverse conformational structures including partial cone, pinched partial cone, 1,2-alternate and twisted 1,2-alternate, depending on the nature of bridging moieties. On the basis of (1)H NMR spectra, homo[2] and homo[4] heterocalix[2]arene[2]triazines were fluxional macrocycles in solution, and they underwent rapid conformation interconversion at different temperatures. Efficient and straightforward nucleophilic aromatic substitution reaction and palladium-catalyzed cross-coupling reactions on chlorotriazine rings, and the nucleophilic alkylation reaction on the bridging nitrogen atoms led to the construction of various highly functionalized homo heterocalix[2]arene[2]triazine derivatives.

Electronic Properties of Unprecedented Bridging Organoimido-Substituted Hexamolybdate: New Insights from Density Functional Theory Study

The organoimido functionalization of polyoxometalates (POMs) has drawn tremendous attention due to particular merits in fabricating POM-based hybrid materials with finely tunable properties. The electronic properties, orbital and bonding characters of unprecedented bridging organoimido-substituted hexamolybdate are investigated using density functional theory methods. Among the organoimido-bridged hexamolybdates, [Mo(6)O(16)(2,6-Me(2)-NC(6)H(3))(2)(mu(2)-2,6-Me(2)-NC(6)H(3))](2-) (3-Ar-1), which features two terminal and one bridging organoimido ligand, is more favorable. The calculations confirm that the three-center (3c) pi bond originates from the coplanarity of bridging nitrogen atom with two Mo atoms and the hybridization of bridging nitrogen. The 3c bond stabilizes the organoimido-bridged anion 3-Ar-1. Compared with cis-bifunctionalized organoimido derivative [Mo(6)O(17)(2,6-Me(2)-NC(6)H(3))(2)](2-) (2-Ar), the bonding interaction between terminal organoimido ligand and hexamolybdate cluster in 3-Ar-1 is strengthened by the bridging organoimido. The results are in good agreement with the analysis of the Wiberg bond index of the Mo-N bond. The organoimido segment modifies the occupied molecular orbitals of organoimido hexamolybdates. The unoccupied molecular orbitals in 3-Ar-1 are largely nonbonding O(p) and Mo(d) orbitals in character, which resemble those of 2-Ar.

Synthesis of Amino‐Bridged Oligosaccharide Mimetics

AbstractSynthesis of amino‐bridged oligosaccharides using reductive amination opens rapid access to novel glycomimetic target structures as potential ligands for the receptor protein NKR P1 of natural killer cells. Emphasis was laid on fast and facile synthetic routes. The carbonyl building blocks were easily obtained by oxidation with Dess–Martin periodinane or iodoxybenzoic acid (IBX). For the required amino‐functionalized units, reduction of azide precursors was advantageous, and generation of the novel oligosaccharides was achieved by subsequent reductive amination. The target saccharide structures feature a bridging nitrogen atom inserted between two non‐anomeric positions as well as including one anomeric position.

ChemInform Abstract: Heterocycles with a Bridging Nitrogen Atom. Part 19. Developement of Routes for the Synthesis of Oxazoloisoquinolinium Salts Based on Phenacylation of α‐Methyl‐1(3)‐isoquinolones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Coordination polymers containing ferrocene backbone. Synthesis, structure and electrochemistry

The reaction of 1,1'-ferrocenedicarboxylic acid (LH(2)) with bis(triphenyltin) oxide afforded a molecular heterobimetallic compound [(Ph(3)Sn)(2)L]. In the latter the two carboxylate units of [L](2-) are involved in an anisobidentate chelating coordination mode to two triphenyl tin units. The reaction of LH(2) with trimethyltin hydroxide or bis(tri-n-butyltin) oxide afforded 2D-coordination polymers [(Me(3)Sn)(2)L](n) and [(n-Bu(3)Sn)(2)L](n) which are formed as a result of anisobidentate bridging coordination action of the two carboxylate units of [L](2-). Interestingly the 2D-coordination polymers contain 24-membered macrocycles each of which is comprised of four trialkyl tin units. The coordination unsaturation of [(Ph(3)Sn)(2)L] can be utilized to form coordination polymers. Accordingly the reaction of LH(2) with bis(triphenyltin) oxide in the presence of ditopic nitrogen ligands such as 4,4'-bipyridine, 4,4'-trimethylenebipyridine or 4,4'-vinylenebipyridine afforded one-dimensional coordination polymers which contain in their backbone three distinct structural components viz., two triorganotin units, a ferrocenyl unit and a bridging nitrogen ligand unit. The coordination polymers, however, do not retain their structural integrity in solution and fall apart to their monomeric units. Electrochemical studies on these hybrid orgaonotin/ferrocene systems reveal that most of them exhibit a single quasi-reversible oxidation peak.

Recognition of amino acids and anions by a Zn(II)-methylazacalix[4]pyridine complex

As a powerful macrocyclic host molecule with unique conformation and cavity structure that are fine-tuned by the bridging nitrogen atoms, methylazacalix[4]pyridine (MACP-4) has been shown to selectively recognize Zn2+ and form stable Zn(II)-MACP-4 complexes both in solid state and solution with an association constant up to 5.97 (logKs). The molecular recognition of Zn(II)-MACP-4 complexes towards various amino acids and anions with different geometry was investigated by using the spectral titration methods and X-ray analysis. The Zn(II)-MACP-4 complex was found to recognize the 17 amino acids tested with the association constant up to 3.97 (logKs). On the other hand, the Zn(II)-MACP-4 complex selectively interacted with anions and the maximum association constant of 3.9 (logKs) was obtained.

Synthesis and antimicrobial activity of pyrimidinophanes with two uracil units and bridging nitrogen atoms

A series of pyrimidinophanes containing two uracil units and nitrogen atoms in bridging polymethylene chains –(CH2) n N(Et)(CH2) m – (n, m = 5, 6) have been synthesized. The uracil moieties are represented by 6-methyl-, 5-decyl-6-methyl-, and 5-fluorouracils. Quaternization of the bridging N atom with ethylbromide or n-decylbromide yielded amphiphilic pyrimidinophanes, which were evaluated for their antibacterial and antifungal activity in terms of minimal inhibiting concentration (MIC) against Gram-positive and Gram-negative bacteria and fungi. It has been found that MICs of the amphiphilic pyrimidinophanes decrease with increasing lipophilicity of the alkyl substituents at the bridging N atoms and with increasing polymethylene N(pyr)–N chain length (in some cases MIC against Staphylococcus aureus is below 1 ig/mL). The MICs increase dramatically upon introduction of lipophilic n-decyl substituents at C(5) atoms of the uracil moiety. The results can be used in the search for new highly effective antimicrobial agents.

Titanium complexes containing new dianionic tetradentate [ONNO]-type ligands with benzyl substituents on bridging nitrogen atoms: Syntheses, X-ray structures, and catalytic activities in ring opening polymerization of lactide

Several titanium isopropoxides 1– 8 have been prepared by the reaction of Ti(O- i-Pr) 4 with a series of corresponding tetradentate Salan-type [ONNO] ligands with benzyl or methyl substituents on bridging nitrogen atoms. They have been characterized by 1H NMR, 13C{ 1H} NMR, and elemental analysis. Solid state structures of compounds 2, 4, 6, and 7 have been determined by X-ray crystallography. X-ray diffraction analysis and 1H NMR confirmed that these titanium complexes were all monomeric species with a six-coordinated central titanium in their solid and solution structures. Complexes 2, 4, 6, and 8 with benzyl substituents on bridging nitrogens gave PLA with higher molecular weight than compounds 1, 3, 5, and 7 with methyl substituents did.

Azacalix[4]arene tetramethyl ether with inherent chirality generated by substitution on the nitrogen bridges

The first inherently chiral azacalix[4]arene has been prepared by introducing three benzyl groups onto the nitrogen bridges. The highly enantioenriched compound was easily obtained via a moderately enantioselective cyclization followed by a simple crystallization procedure. NMR and X-ray crystallographic studies revealed that easy access to the enantiomer was permitted by the non-racemizable 1,3-alternate conformation in solution, up to 110 °C, as well as by the preferential crystallization of a racemic compound.

Ligands for Dinitrogen Fixation at Schrock-Type Catalysts

Catalytic dinitrogen reduction with the Schrock complex is still hampered by low turn-over numbers that are likely to result from a degradation of the chelate ligand. In this work, we investigate modifications of the original HIPTN(3)N ligand applied by Schrock and co-workers in catalytic reduction of dinitrogen with density functional methods. We focus on ligands that are substituted in the para position of the central phenyl ring of the terphenyl moieties and on a ligand where the bridging nitrogen is exchanged by phosphorus. In addition, results for tris(pyrrolyl-alpha-methyl)amine, tris(pyrrolyl-alpha-ethyl)amine, and tris[2-(3-xylyl-imidazol-2-ylidene)ethyl]amine are reported. For this study, we take into account the full ligands without approximating them by model systems. Reaction energies for the various derivatives of HIPTN(3)N are found to be similar to those of the unchanged parent system. However, the most promising results for catalysis are obtained for the [{tris[2-(3-xylyl-imidazol-2-ylidene)ethyl]amine}Mo](N(2)) complex. Feasibility of the exchange of NH(3) by N(2) is found to be the pivotal question whether a complex can become a potential catalyst or not. A structure-reactivity relationship is derived which allows for the convenient estimation of the reaction energy for the NH(3)/N(2) exchange reaction solely from the wavenumber of the N[triple bond]N stretching vibration. This relationship may guide experiments as soon as a dinitrogen Mo complex is formed.

Heterocycles with a bridging nitrogen atom. 19. Development of routes for the synthesis of oxazoloisoquinolinium salts based on phenacylation of α-methyl-1(3)-isoquinolones

Alkylation of 3-methyl-1-isoquinolone and 1-methyl-3-isoquinolone with phenacyl bromides proceeds regioselectively with the formation in the first case of only an N-phenacyl derivative and in the second only the O-derivative. The 5-methyl[1,3]oxazolo[3,2-a]isoquinolinium salt has been synthesized and its reactions with ammonia, morpholine, and sodium methylate have been investigated.

Double helix of the coordination polymer of silver with 1,3-bis(4-pyridyl)propane: Synthesis and crystal structure of [Ag(C13H14N2)](CF3CO2)

The [Ag(Bpp)](CF3CO2) complex (Bpp is 1,3-bis(4-pyridyl)propane, C13H14N2) is synthesized, and its structure is determined. The crystals are monoclinic, space group C2/c, a = 26.169(5), b = 10.521(2), c = 12.906(3) A, β = 117.99(3)°, V = 3137.7(11) A3, ρcalcd = 1.775 g/cm3, Z = 8. The structure contains double helices of-Ag-Bpp-Ag-Bpp-cationic chains with a helix period of 21.042 A. The Ag…Ag distance between a pair of silver atoms from different chains in the helix is 3.201 A, and the distance between the adjacent helices is 3.279 A. The silver atom is linked with two bridging nitrogen atoms of two Bpp ligands in an almost linear coordination: Ag-Navg 2.142 A; NagN, 171.3(4)°. The CF3C2− anion has a weak contact with the silver ion (Ag…O 2.62(2) A).