Pyridine Adducts Research Articles

Air-Stable Gadolinium Precursors for the Facile Microwave-Assisted Synthesis of Gd2O3 Nanocontrast Agents for Magnetic Resonance Imaging

Using metal organic precursors in materials synthesis remains a challenge due to their high moisture susceptibility. In this work, we describe a facile methodology for the synthesis of Gd2O3-based contrast agents from two new gadolinium-based complexes. [Gd(PyTFP)4] (PyH) 1 (PyTFP = C8H5NOF3, Py = C5H5N) and [Gd(DMOTFP)3Py] 2 (DMOTFP = C8H7NO2F3) were synthesized via a classical ligand exchange reaction of [Gd{N(SiMe3)2}3] under inert conditions. As a result, X-ray diffraction analysis revealed a distorted square antiprismatic coordination and an augmented triangular prismatic arrangement of ligands around gadolinium atoms in 1 and 2, respectively. It also showed that 1 is an anionic complex of formula [Gd(PyTFP)4](PyH), while a neutral tris-compound, [Gd(DMOTFP)3Py], was obtained as a pyridine adduct in 2. Fast and reproducible microwave-assisted decomposition of 1 and 2 provided homogeneous Gd(OH)3 nanorods at mild temperature without using any surfactant or capping reagent. As-synthesized nanorods were...

Structural diversity in pyridine and polypyridine adducts of ring slipped manganocene: correlating ligand steric bulk with quantified deviation from ideal hapticity.

We have synthesized several new manganocene-adduct ([Cp2Mn(L)] = 1-L) complexes using pyridine and polypyridine ligands and report their molecular structures and characterization data. Consistent with other molecules in this class [(ηx-Cp)2MnLn] or [(ηx-Cp)2Mn(L-L)] (n = 1, 2; x = 1, 3, or 5), the manganese-cyclopentadienide interaction deviates from the classical ηx interactions (x = 3 or 5). Such deviations have been ascribed to steric factors and often called non-ideal hapticity. However, there is no quantification of this non-ideal hapticity and thus it is difficult to evaluate the extent of ring slippage or assign hapticity. Furthermore, the hypothesis that non-ideal hapticity in high-spin MnII complexes is induced by steric interactions has not been systematically evaluated. Therefore, we report herein a quantified scale for deviation from ideal hapticity between zero (ideal η5 interaction) and one ("η1" interaction). This quantified deviation from ideal hapticity has an empirical relationship with the ligand's steric properties, which strongly supports the premise that steric interactions cause the deviations in ionic M-Cp interactions.

Structural effect in the reductive vinylation/phosphorylation of pyridines with alkyl propiolates and secondary phosphine chalcogenides: protonation vs. zwitterion generation

The non-catalyzed reaction of 2- and 3-substituted pyridines with alkyl propiolates and secondary phosphine chalcogenides (50–52 °C, MeCN) produces stereo-, regio- and chemoselectively 1-[(E)-2-(alkoxycarbonyl)ethenyl]-4-chalcogenophosphoryl- 1,4-dihydropyridines in 57–90% yields, the adducts of pyridines with alkyl propiolates being the zwitterionic intermediates. 4-Methylpyridine mainly catalyzes nucleophilic addition of secondary phosphine chalcogenides to alkyl propiolates.

Crystal structure and Hirshfield analysis of the 4-(di-methyl-amino)-pyridine adduct of 4-meth-oxy-phenyl-borane.

The title compound [systematic name: 4-(di-methyl-amino)-pyridine-4-meth-oxy-phenyl-borane (1/1)], C14H19BN2O, contains two independent mol-ecules in the asymmetric unit. Both molecules exhibit coplanar, mostly sp2-hybridized meth-oxy and di-methyl-amino substituents on their respective aromatic rings, consistent with π-donation into the aromatic systems. The B-H groups exhibit an intra-molecular close contact with a C-H group of the pyridine ring, which may be evidence of electrostatic attraction between the hydridic B-H and the electropositive aromatic C-H. There appears to be weak C-H⋯π(arene) inter-actions between two of the H atoms of an amino-methyl group and the meth-oxy-substituted benzene ring of the other independent mol-ecule, and another C-H⋯π (arene) inter-action between one of the pyridine ring H atoms and the same benzene ring.

On the Redox Reactivity of a Geometrically Constrained Phosphorus(III) Compound.

The reactivity of a geometrically constrained phosphorus(III) complex bearing the N,N-bis(3,5-di-tert-butyl-2-phenolate)amide pincer ligand (P(ONO); 1) towards oxidants and reductants is explored. This compound can be readily oxidized to the phosphorus(V) dihalo-derivatives P(ONO)X2 where X=Cl (2), Br (3) and I (4). Attempts at isolating the analogous difluoride through oxidation of 1 were unsuccessful yielding only the hydrofluoride P(ONO)(H)F (5), however P(ONO)F2 (6) can be accessed via a halide exchange reaction of 2 with KF. Compound 2 can be employed as a precursor to novel cationic species through chloride ion displacement using strong Lewis bases. Thus, reaction of 2 with two or three molar equivalents of dimethylaminopyridine (DMAP) affords [P(ONO)(Cl)(DMAP)2 ]+ (7) and [P(ONO)(DMAP)3 ]2+ (8). Reaction of 2 with the weaker bidentate base 2,2'-bipyridine (bipy) affords [P(ONO)(Cl)(bipy)]+ (9), although this species was only accessible upon addition of a halide abstracting agent. The dicationic tris(pyridine) adduct [P(ONO)(py)3 ]2+ (10) is also accessible by reaction of 4 with pyridine. Oxidation of 1 using oxygen gas proceeds slowly and allows for the observation of two compounds, a mixed valence dimeric phosphorus(III)/phosphorus(V) compound [P(ONO)(μ2 -O)(μ2 :κ1 ,κ2 -ONO)P] (11) and the fully oxidized species [P(ONO)(μ2 -O)(μ2 :κ1 ,κ2 -ONO)P(O)] (12). Finally, reaction of 1 using KC8 results in the dimerization of the putative radical anion [P(ONO)].- through formation of a P-P bond to afford [P(ONO)]22- (13). Reactions with TEMPO result in the formation of the trigonal bipyramidal species P(ONO)(TEMPO)2 (14).

Preparation and Characterization of Group 13 Cyanides.

Binary Group 13 cyanides [PPh4 ][Ga(CN)4 ], [PPh4 ]2 [In(CN)5 ], and [PPh4 ]2 [Tl(CN)5 ] were obtained in quantitative yields from the corresponding metal trifluorides MF3 (M=Ga, In, Tl) by fluoride-cyanide exchange reactions with Me3 SiCN in the presence of stoichiometric amounts of [PPh4 ]CN in acetonitrile solution. The 2,2'-bipyridine (bipy) adducts [(bipy)2 Ga(CN)2 ][Ga(CN)4 ], [(bipy)In(CN)3 ], and [(bipy)Tl(CN)3 ] were obtained from the reaction of MF3 with Me3 SiCN and bipy in acetonitrile. While the reaction of the metal trifluorides with Me3 SiCN in acetonitrile resulted in recovery of the starting materials, the reaction of MF3 with Me3 SiCN in pyridine (py) solution resulted in the formation of the pyridine adducts [(py)2 Ga(CN)3 ], [(py)3 In(CN)3 ], and [(py)2 Tl(CN)3 ]. The cyano compounds were characterized by their vibrational spectra and, in most cases, by their X-ray crystal structures.

From Bidentate Gallium Lewis Acids to Supramolecular Complexes.

Bidentate gallium Lewis acids were prepared by the reaction of diethynyldiphenylsilane with neat trimethyl- or triethylgallium. Bis[(dimethylgallyl)ethynyl]diphenylsilane (1) and diethylgallyl derivative 2 were characterized as Et2 O or pyridine adducts by NMR spectroscopy; 2⋅2Py was isolated. Lewis acids 1 and 2 form host-guest adducts with bidentate nitrogen bases, but defined cyclic 1:1 adducts are only formed between 1 and bases with matching N⋅⋅⋅N distances: 4,4'-dimethyl-3,3'-bipyridinylacetylene (3), bis[(pyridin-3-yl)ethynyl]diphenylsilane (4), and bis[(2-methylpyridin-5-yl)ethynyl]diphenylsilane (5). The structures of adducts 1⋅3, 1⋅4, and 1⋅5 were established by X-ray diffraction experiments. 2⋅2Py reacts with DABCO to afford polymeric (DABCO-2-)n .

Aerosol-Assisted Chemical Vapor Deposition of CdS from Xanthate Single Source Precursors

Bis-3-methylpyridine and bis-4-methylpyridine complexes of cadmium(II) ethylxanthate have been characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis. The single crystal X-ray structures of both methylpyridine derivatives have also been determined and shown to display a cis, cis, cis-configuration of the N- and S-donor ligands. The compounds have been utilized as single source precursors to deposit CdS films on silica-coated glass substrates at 220 and 350 °C by aerosol-assisted chemical vapor deposition. The surface morphology of the films has been examined by scanning electron microscopy analysis and the crystalline phases were studied by powder X-ray diffraction. The films deposited from the 3-methylpyridine adduct comprised more densely packed and more highly crystalline hexagonal CdS than those provided by either of the other two precursors. The crystallite sizes were found to be <20 nm for films deposited from the pyridine and 4-methylpyridine adducts but to display a ...

Green Synthesis of Copper Triflusalate and Pyridine Adducts

AbstractConventional organic solvents are the preferred media to prepare and crystallize metallorganic materials, since the wide diversity of organic solvents allows the control of solubility parameters and precipitation kinetics. However, they are the largest waste input in fine chemical synthesis; and moreover, in the processing of materials with ester containing groups, which have a significant tendency to hydrolysis, the use of organic solvents can be too aggressive to keep the structure of labile molecules. In this context, milder methods to prepare crystalline metallorganic derivatives of triflusal (HTrf), a drug bearing an ester group, are here described. HTrf molecule itself and its derivatives have important applications in the pharmaceutical industry. In this work, copper triflusalate complexes and derived pyridine adducts are prepared via an environmentally friendly supercritical CO2 method, preserving the ester group from hydrolysis. For comparison, some intricate conventional solvent liquid methods are also envisaged. Products are fully characterized in regard of composition, structure and magnetic properties.

Mixed Ligated Tris(amidinate)dimolybdenum Complexes as Catalysts for Radical Addition of CCl4 to 1-Hexene: Leaving Ligand Lability Controls Catalyst Activity.

We synthesized a series of mixed ligated tris(amidinate)dimolybdenum complexes, namely, [Mo2(DAniF)3(L)] [DAniF = N,N'-di(p-anisyl)formamidinate; L = acetate (OAc; 1a), m-diphenylphosphino benzoate (m-PPh2Bz; 1b), nicotinate (Nico; 1c), benzoate (Bz; 1d), 3-furoate (3-Furo; 1e), isonicotinate (IsoNico; 1f), and trifluoromethanesulfonate (OTf; 1g)], which served as catalysts for radical addition of CCl4 to 1-hexene to give 1,1,1,3-tetrachloroheptane. These mixed ligated complexes 1a-g afforded the higher yield of the radical addition product than a homoleptic DAniF complex, [Mo2(DAniF)4] (2). Among them, complexes 1a and 1g gave the radical addition product quantitatively after 9 h with a short induction period. When complexes 1a and 1g were treated with CCl4, we detected the mixed-valence Mo2(II/III) complex, [Mo2(DAniF)3Cl2] (4), in electrospray ionization mass spectrometry measurements, indicating that the leaving nature of the L ligands was a crucial factor for initiating the catalytic reaction: the catalytic activity of the carboxylate-bridged complex 1a and the triflate-bridged complex 1g in the initial 30 min highly depended on the ligand-exchange rate of L, as estimated by monitoring the reaction with CCl4 in pyridine, giving the pyridine adduct complex, [Mo2(DAniF)3Cl(py)] (3).

Long-Lived Five-Coordinate Platinum(IV) Intermediates: Regiospecific C–C Coupling

Three different phosphine derivatives of doubly cyclometalated diphenypyridine complexes of Pt(II), 1, were reacted with methyl iodide to give octahedral Pt(IV) complexes, 2, as two isomers. Treatment of either isomer of complexes 2 with AgBF4, to abstract iodide, gave long-lived five-coordinate complexes 3, which could be trapped as pyridine adducts. Complexes 3 underwent a C–C coupling reaction, at a rate that depended on phosphine size, to give a methyl group attached to the original diphenylpyridine. Recylometalation was then performed, and the cycle of reactions was repeated to give a diphenylpyridine doubly methylated on only one phenyl, with complete regiospecificity. NMR was used to demonstrate the geometry of all complexes in solution, with multiple X-ray crystal structures confirming these assignments.

SiSxHy]n – Perhydridopolysilathianes: Cross‐Linked Thio Analogues of Polysiloxanes

Polysiloxane‐analogous Si–S compounds have so far not been reported. Transsilylation reactions of the solid pyridine adduct of HSiCl3 with gaseous Me3Si–S–SiMe3 yielded perhydridopolysilathianes. 29Si NMR, FTIR, and Raman spectroscopy; elemental and thermal analysis; XRD; SEM; and gas‐adsorption measurements indicated that the product consists of D‐, T‐, and Q‐units with a composition of ([H2SiS]1.2[HSiS1.5]2.6[SiS2]1.0)n. Formation of the latter is caused by pyridine‐catalyzed dismutation reactions. The polymer is mesoporous with a surface area of 187 m2 g–1; furthermore, it is amorphous and insoluble in organic solvents.

Formation of Oxazoles from Elusive Gold(I) α-Oxocarbenes: A Mechanistic Study.

The gold(I) catalyzed reaction between phenylacetylene, pyridine N-oxide and acetonitrile leading, via a putative gold-α-oxocarbene intermediate, towards an oxazole product has been investigated. A novel mass spectrometric method called "delayed reactant labeling" is used to track consecutive and parallel reactions. It clearly shows that the intramolecular formation of a pyridine adduct of gold-α-oxocarbene is in competition with the formation of the oxazole product. The reaction mechanism most probably corresponds to competition between acetonitrile and pyridine in an almost barrierless reaction with putative gold-α-oxocarbene within the solvent cage. The detected ionic species have been characterized by helium tagging infrared photodissociation spectroscopy.

Corrigendum to: Quantum-chemical Ab Initio Calculations on the Donor–Acceptor Complex Pyridine–Borabenzene (C5H5N–BC5H5)

The adduct of borabenzene (C5H5B) and pyridine (C5H5N) was studied by means of quantum-chemical ab initio and time-dependent density functional theory calculations at different levels of theory. In the fully optimized structure (MP2/6-311++G**) of the free donor–acceptor complex (C2), the C–B–C angle amounts to 120.6°. The planes of the two aromatic rings enclose a torsion angle of ~40° with a barrier to rotation about the B–N bond of less than 3kcalmol–1 (1kcalmol–1=4.186kJmol–1). The highest computational level applied in this study (complete basis set limit, coupled cluster with single and double excitations (CCSD)) results in an energy associated with the reaction of borabenzene with pyridine of –52.2kcalmol–1. Natural bond orbital analyses were performed to study the bond between the borabenzene and the pyridine unit of the adduct. The UV-vis spectrum of the adduct was calculated employing time-dependent density functional theory methods and the symmetry-adapted cluster-configuration interaction method. Our calculated electronic excitation spectrum of the pyridine adduct as well as its spectrum of the normal modes qualitatively reproduce the characteristic features of the IR and the UV-vis spectra described by experimentalists and thus allows assignment of the observed absorption bands, which in part agree with those by other authors.

Surface-Electrolyte Interphase Formation in Lithium-Ion Cells Containing Pyridine Adduct Additives

The use of electrolyte additives to form a passive solid-electrolyte interphase (SEI) at one or both electrodes is a common method for improving lithium-ion cell lifetime and performance. This work follows the chemical and electrochemical processes involved in SEI formation on graphite electrodes for two Lewis acid-base adducts, pyridine boron trifluoride (PBF) and pyridine phosphorus pentafluoride (PPF). The combination of experimental methods (electrochemistry, in situ volumetric measurements, gas chromatography, isothermal microcalorimetry, and X-ray photoelectron spectroscopy) with quantum chemistry models (density functional theory) provides new insight into the interfacial chemistry. PBF and PPF are reduced at ∼1.3 V vs. Li/Li+ and ∼1.4 V, respectively. This is followed by radical coupling to form 4,4′-bipyridine adducts, hydrogen transfer to ethylene carbonate solvent molecules, and reduction of the solvent to produce lithium ethyl carbonate. The reduced bipyridine adducts, Li2(PBF)2 and Li2(PPF)2, are shown to compose part of the SEI at the negative electrode surface.

A 1,1-Carboboration Route to Bora-Nazarov Systems.

Hydroboration of the conjugated enynes 1 a and 1 b with Piers' borane [HB(C6F5)2] gave the respective dienylboranes trans-2 c and trans-2 d. Their photolysis resulted in the formation of the dihydroborole products 3 c and 3 d. Both were converted to their pyridine adducts 5 c and 5 d, respectively. Compounds 3 c and 5 c,d were characterized by X-ray diffraction. The reaction of the bis(enynyl)boranes 6 a and 6 b with B(C6F5)3 resulted in the formation of the dihydroboroles 7 a and 7 b, respectively. This reaction is thought to proceed by 1,1-carboboration of one of the enynyl substituents at boron to generate the dienylborane intermediates 8 a/8 b, followed by thermally induced bora-Nazarov ring-closure and subsequent stabilizing 1,2-pentafluorophenyl group migration from boron to carbon. Compound 7 a was characterized by X-ray diffraction and solid-state (11)B NMR spectroscopy.

ChemInform Abstract: Organocatalytic Enantioselective Direct Additions of Aldehydes to 4‐Vinylpyridines and Electron‐Deficient Vinylarenes and Their Synthetic Applications.

AbstractFor example, the nitro group can be easily transformed to diverse functionalities and a chiral pyridine adduct is accessible which serves as key building block in the synthesis of the fibrinogen receptor antagonist L‐734,217 (not shown).

One-Pot Synthesis of Oligo-Ladder Phenylsilsesquioxanes via Pyridine–Silicon Adduct Formation at Aqueous–Organic Liquid Boundary

Three kinds of oligo-ladder polyphenylsilsesquioxanes were synthesized by two unique methods through the aqueous–organic boundary reaction via octahedrally-coordinated pyridine–silicon adduct PhSiCl3(Py)2, which is formed from trichlorophenylsilane (TCP) monomer and pyridine in n-propyl acetate. When two equivalent pyridines to TCP were used, SQ polymer-1 was formed as a viscous solid, which was recrystallized in n-hexane to obtain SQ polymer-2B. When an excess pyridine was used (pyridine/Si = 10), SQ polymer-2A was directly obtained as a white solid. MALDI–TOF/TOF–MS, FT-IR and 29SiNMR clearly shows that the “Ladder” structure of SQ polymers is dominant in both methods. It was shown that in this one-pot synthesis, SQ polymer structure was controlled by pyridine amount. Furthermore, MO simulation of pyridine adduct formation (PhSiCl3(Py)2) supports the hydrolysis pathway for synthesis as well as the “Ladder” structure formation. Finally, it was also suggested that the hydrolysis reaction occurred in a stepwise manner.

Organocatalytic enantioselective direct additions of aldehydes to 4-vinylpyridines and electron-deficient vinylarenes and their synthetic applications.

We describe a synergistic catalysis strategy for the asymmetric direct addition of simple aldehydes to 4-vinylpyridines. By means of independent activation of weakly electrophilic 4-vinylpyridines by the Brønsted acid CF3SO3H (TfOH) and aldehydes by chiral diphenylprolinol tert-butyldimethylsilyl (TBDMS) ether-catalyzed formation of nucleophilic enamines in a cooperative manner, the previously unattainable highly enantioselective addition process has been realized for the first time. Notably, the power of the addition process is fueled by its high efficiency in the production of synthetically valued chiral pyridines. (1)H NMR studies of the process suggested that the nucleophilic enamine formed in situ from the chiral amine catalyst and the aldehyde is directly added to the trimeric 4-vinylpyridinium-derived species as a highly active electrophile generated from the 4-vinylpyridine in the presence of TfOH. Moreover, inspired by the similar electronic natures of pyridine and nitrobenzene, we have achieved an unprecedented chiral diphenylprolinol TBDMS ether-promoted, highly enantioselective direct addition of aldehydes to 2-nitrostyrenes without the use of TfOH as a cocatalyst. In this approach, introducing a strong electron-withdrawing group such as NO2, CF3, SO2Me, etc. on the 2-nitrostyrene creates a highly electrophilic vinyl moiety, which enables the direct addition of the in situ-formed enamine derived from the chiral amine promoter and the aldehyde. This method significantly expands the scope of the enantioselective addition process. While the electron-withdrawing nitro group is essential for activation of the vinyl group, we have demonstrated that it can be readily transformed to diverse functionalities. Furthermore, as shown, a chiral pyridine adduct serves as a key building block in the synthesis of the potent fibrinogen receptor antagonist L-734,217.

Structure determination of bound nitrogen-based adducts with copper(II) acetylacetonato; an EPR, ENDOR and DFT study.

The adducts of bis(acetylacetonato)–copper(II), [Cu(acac)2], formed with a range of nitrogen heterocycles including pyridine (2), methylpyridines (3,4,5), amino-methylpyridines (6,7) and diazines (8,9,10) were investigated in frozen solution using X-band EPR and 1H ENDOR spectroscopy. The small perturbations to the EPR spin Hamiltonian parameters (g and CuA) were consistent with the axial coordination of the nitrogen bases to Cu(II), and found to be dependent on both the basicity and steric influence of the coordinating substrate. The detailed structure of two adducts was then investigated by angular selective (1)H ENDOR and DFT. For the [Cu(acac)2](pyridine) adduct, axial coordination of the substrate was found to occur via the pyridine nitrogen as expected, producing a characteristic (1)H hyperfine coupling ((H)Ai = −2.6, −2.04, 4.7 MHz; β = 36°; aiso = 0.2 MHz) arising from the ortho-(1)H in the ring 2 or 6 position. These results were confirmed by DFT. However, in the [Cu(acac)2](2-amino-6-methyl-pyridine) adduct, the ENDOR data revealed a substantially different (1)H hyperfine coupling ((H)Ai = −4.52, −3.35, 6.47 MHz; β = 14°; aiso = −0.47 MHz) arising from the –NH2 amino protons. Analysis of this experimentally derived tensor in conjunction with the calculated DFT tensors, revealed that the 2-amino-6-methyl-pyridine substrate binds to Cu(II) via the exocyclic amino pyridine nitrogen, but with a tilt angle of 20° of the pyridine ring away from the geometry optimised structure. These results reveal how important structural information on the coordination geometry of Cu(II) adducts can be obtained by (1)H ENDOR, but only when the complete angular dependency profile of the ENDOR data is thoroughly considered.