Synthesis and physicochemical characteristics of the adducts of 6-thio-nido-decaborane(11) with pyridine bases

A series of adducts SB₉H₁₁·L (L=Py, 4-Pic, 4,4-Dipy, SB₉H₁₁·4,4-Dipy) were synthesized and studied by IR,¹¹B NMR, and x-ray photoelectron spectroscopy. Substitution of the HB·L fragment by a sulfur atom in the B₁₀H₁₂·L₂ adducts leads to a decrease in the electron density at the boron atoms on account of its attraction to the sulfur atom. According to the XPS data, the charge state of the sulfur in the investigated SB₉H₁₁·L compounds is similar to the state in dialkyl sulfides.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2113–2118, September, 1990.     

Reactions of potentially tautomeric methyl and methylene derivatives of pyridine and diazines with N-electrophiles (review)

Data on the nitration, nitrosation, azo-coupling, and electrophilic amination of potentially tautomeric methyl and methylene derivatives of a series of pyridines, pyridazines, pyrimidines, and pyrazines in media of varying acidity and basicity are reviewed systematically. Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 147–162, February, 1998.     

Nuclear Overhauser effect (NOE) enhancement of 11B NMR spectra of borane adducts in the solid state

A strong 11B {1H} nuclear Overhauser effect (NOE) enhancement can be observed in solid-state 11B NMR spectra of borane adducts, yielding fractional enhancements, fI{S} = (I - I0)/I0, of the magic angle spinning (MAS) NMR signal of up to 155%. This is an interesting and unusual observation as 11B (spin I = 3/2) is a quadrupolar nucleus and the corresponding NOE is completely absent in solution. More generally, it shows that the NOE may have a wider role to play in solid-state NMR studies of dynamics than has been envisaged hitherto.     

Iridium-catalyzed asymmetric hydrogenation of pyridine derivatives, 7,8-dihydro-quinolin-5(6H)-ones

[Ir(COD)Cl]₂/MeO-Biphep/I₂ catalyst system is highly effective for asymmetric hydrogenation of pyridine derivatives 7,8-dihydro-quinolin-5(6H)-ones with high enantioselectivities (up to 97% ee).     

Hydrogen exchange,alkylation and acylation of potentially tautomeric methyl and methylidene derivatives of pyridine and diazines (Review)

Summary Data on the deuteration, alkylation and acylation reactions of potentially tautomeric methyl and methylidene derivatives of pyridine, pyrimidine and pyrazine in media of varying acidity and basicity have been collated. Whether these reactions occur via the aromatic tautomers, the more reactive methylidene tautomers or predominantly by generation of mesomeric anions from both tautomers is examined.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 816–829, June, 1995. Original article submitted May 16, 1995.     

NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives

Substituted pyrazolopyridines are potent inhibitors of phosphodiesterases and cyclin-dependent kinases. In this study, NMR was used to investigate the potential N1-H and N2-H tautomerism of 5-substituted pyrazolo[3,4-c]pyridine derivatives. Six compounds were fully characterized by using (1)H, (13)C, and (15)N chemical shifts and indirect (1)H--(13)C and (1)H--(15)N coupling constants. The (1)H NMR spectra were measured over a broad range of temperatures. All of the compounds were shown to exist predominantly in the N1-H tautomeric form. Complementary quantum-chemical calculations of the chemical shieldings and indirect spin-spin couplings support the structural conclusions drawn.     

The NMR spectra of some fluorinated pyridine derivatives

The ¹H and ¹⁹F spectra of a variety of mono- and di- fluorinated pyridines are examined, and compared with the corresponding spectra of the pyridinium ions. The magnitudes and signs of the ¹H? ¹⁹F coupling constants are in general in accord with those observed for the corresponding ¹H? ¹H couplings, with an exaggerated range. Large changes in the NMR parameters are observed on protonation of the nitrogen, ³J(H? F) changing sign in some of the α-fluoropyridine derivatives.     

Thermochemistry of adducts of some transition metals(II) bromides with pyridine N-oxide

The compounds [MBr₂(pyNO)_n] (where M: Mn, Fe, Co, Ni, Cu or Zn; pyNO is pyridine N-oxide and n=2, 3 or 6) were synthesized and characterized by melting points, elemental analysis, thermal analysis and electronic and IR spectroscopy. The enthalpies of dissolution of the adducts, metal(II) bromides and pyNo in methanol were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_rH^θ), the standard enthalpies of formation (Δ_fH^θ), the standard enthalpies of decomposition (Δ_DH^θ), the lattice standard enthalpies (Δ_MH^θ) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Δ_rH^θ(g)). The mean bond dissociation enthalpies of the M(II)-oxygen bonds () have been estimated.     

Microbiological transformation of pyridine derivatives (review)

The pathways in the microbiological transformation of pyridine and its derivatives (alkylpyridines, hydroxypyridines, pyridinecarboxylic acids, alkaloids, and condensed systems with a pyridine ring) under the influence of various microorganisms and several enzyme systems are examined. It is noted that oxidation, reduction, hydrolysis, and destruction of the aromatic ring are the most characteristic processes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1299–1313, October, 1978.     

Ligand adducts of bis(acetylacetonato)iron(II): a 1H NMR study

We report here a thorough (1)H NMR study of Fe(acac)(2) solutions in a wide variety of noncoordinating and coordinating solvents, as well as the interaction of this complex with Et(3)N, pyridine, PMe(2)Ph, and R(2)PCH(2)CH(2)PR(2) [R = Ph (dppe), Et (depe)] in C(6)D(6). The study reveals that Fe(acac)(2) is readily transformed into Fe(acac)(3) in solution under aerobic conditions and that the commercial compound is usually contaminated by significant amounts of Fe(acac)(3). The (1)H NMR resonances of Fe(acac)(2) are rather solvent-dependent and quite different than those reported in the literature. The compound is unstable in CDCl(3) and stable in CD(2)Cl(2), C(6)D(6), CD(3)CN, acetone-d(6), DMSO-d(6), THF-d(8), and CD(3)OD. The addition of the above-mentioned ligands (L) reveals only one paramagnetically shifted band for each type of acac and L proton, the position of which varies with the L/Fe ratio, consistent with rapid ligand exchange equilibria on the NMR time scale. A fit of the NMR data at a high L/Fe ratio allows the calculation of the expected resonances for all protons in the Fe(acac)(2)L(2) molecules. The system with the bidentate depe ligand shows evidence for a slow ligand exchange at low depe/Fe ratios, proposed to involve a species with the cis-chelated mononuclear Fe(acac)(2)(depe) structure, whereas the fast exchange at a higher ratio is proposed to involved a trans-Fe(acac)(2)(κ(1)-depe)(2) complex. Complex Fe(acac)(2)(dppe) cannot be investigated in solution because of low solubility in a noncoordinating solvent and because of the poor dppe competition for binding in coordinating solvents. The compound was crystallized, and its X-ray structure reveals a 1-dimensional polymeric structure with dppe-bridged Fe centers having the trans-octahedral Fe(acac)(2)(κ(1)-dppe)(2) coordination environment.     

Spectrometric study of tautomeric and protonation equilibria of o-vanillin Schiff base derivatives and their complexes with Cu(II)

Electronic absorption and emission properties of a series of Schiff bases derived from 2-hydroxy-3-methoxybenzaldehyde and 2-aminopyridine, 2,3-diaminopyridine, 2,6-diaminopyridine, or 3-aminomethylpyridine were studied in solvents of different polarities. The interconversion of the enolimine to the ketoamine tautomeric form was observed for compound 1, 6-methoxy-2-(3-pyridylmethyliminomethyl)phenol, and the corresponding equilibrium constant was estimated in several solvents. Protonation constants of all the investigated compounds were determined spectrophotometrically in the methanol/water 1/4 system. The effect of copper(II) ions on absorption and on the emission spectra of these ligands was examined in the buffered dioxane/water 1/1 system (pH 5.8). Strong complexation of Cu(II) and formation of a 1:1 complex were observed for the bis-Schiff base derived from 2,3-diaminopyridine. The complex of copper(II) with compound 1 was isolated and characterized by elemental analysis, magnetic susceptibility measurement, UV-vis and IR spectrometry.     

Enthalpies of formation of adducts of antimony(III) iodide with pyridine and methyl-pyridines

Solid adducts of formula SbI₃·L (L = pyridine or 2-, 3- or 4-methylpyridine abbreviated as Py, 2MPy, 3MPy or 4MPy) were synthesized and characterized by elemental analysis, IR spectroscopy and thermal analysis. IR data showed that coordination to antimony is through nitrogen. Thermal degradation of adducts starts at 431, 423, 413 and 411 K for Py, 2MPy, 3MPy and 4MPy, respectively. Reaction-solution calorimetry was used to evaluate the enthalpy change of reaction: SbI₃(cr) + L(l) = SbI₃·L(cr), 61.13 ± 1.75, −82.60 ± 1.55, −67.50 ± 0.97 and −74.10 ± 1.19 kJ mol⁻¹, respectively. Enthalpy change values for decomposition of adducts, lattice enthalpies and enthalpies of the Lewis acid-base reaction in the gas phase were calculated through appropriate thermochemical cycles. Mean SbN bond enthalpies were estimated as 134 ± 3, 154 ± 3, 140 ± 3 and 147 ± 4 kJ mol⁻¹, for Py, 2MPy, 3MPy and 4MPy, respectively.     

Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates

¹¹B and ³¹P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO₅ and BPO₄ represent nearly pure samples, SrBPO₅ contains β-Sr₂P₂O₇ as well as BPO₄ as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO₄ and PO₄ building units. Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996     

Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates

¹¹B and ³¹P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO₅ and BPO₄ represent nearly pure samples, SrBPO₅ contains β-Sr₂P₂O₇ as well as BPO₄ as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO₄ and PO₄ building units. Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996     

Reaction of nido-7,8-C(2)B(9)H(13) with Dicobalt Octacarbonyl: Crystal Structures of the Complexes [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)], [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)], and [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))

The compounds [Co(2)(CO)(8)] and nido-7,8-C(2)B(9)H(13) react in CH(2)Cl(2) to give a complex mixture of products consisting primarily of two isomers of the dicobalt species [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (1), together with small amounts of a mononuclear cobalt compound [Co(CO)(2)(eta(5)-10-CO-7,8-C(2)B(9)H(10))] (5) and a charge-compensated carborane nido-9-CO-7,8-C(2)B(9)H(11) (6). In solution, isomers 1a and 1b slowly equilibrate. However, column chromatography allows a clean separation of 1a from the mixture, and a single-crystal X-ray diffraction study revealed that each metal atom is ligated by a terminal CO molecule and in a pentahapto manner by a nido-C(2)B(9)H(11) cage framework. The two Co(CO)(eta(5)-7,8-C(2)B(9)H(11)) units are linked by a Co-Co bond [2.503(2) ?], which is supported by two three-center two-electron B-H right harpoon-up Co bonds. The latter employ B-H vertices in each cage which lie in alpha-sites with respect to the carbons in the CCBBB rings bonded to cobalt. Addition of PMe(2)Ph to a CH(2)Cl(2) solution of a mixture of the isomers 1, enriched in 1b, gave isomers of formulation [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)] (2). Crystals of one isomer were suitable for X-ray diffraction. The molecule 2a has a structure similar to that of 1a but differs in that whereas one B-H right harpoon-up Co bridge involves a boron atom in an alpha-site of a CCBBB ring coordinated to cobalt, the other uses a boron atom in the beta-site. Reaction between 1b and an excess of PMe(2)Ph in CH(2)Cl(2) gave the complex [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))] (3), the structure of which was established by X-ray diffraction. Experiments indicated that 3 was formed through a paramagnetic Co(II) species of formulation [Co(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))]. Addition of 2 molar equiv of CNBu(t) to solutions of either 1a or 1b gave a mixture of two isomers of the complex [Co(2)(CNBu(t))(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (4). NMR data for the new compounds are reported and discussed.