NMR Spectral Properties Research Articles

Synthesis and Structure of [6](1,4)Naphthalenophane and [6](1,4)Anthracenophane and Their Peri-Substituted Derivatives

Abstract [6](1,4)Naphthalenophane (1a), [6](1,4)anthracenophane (2a), and their peri-substituted derivatives 1b, 1c, and 2b were synthesized from 8-bromo[6]paracyclophane (4) by a benzoannelation method. The 1H NMR spectral properties of 1b, 1c, and 2b as well as the X-ray crystallographic structure analysis of 1b indicate that their bridged aromatic rings are more distorted than those of the corresponding parent systems, 1a and 2a. Thermally reversible photochemical isomerization of 1b and 2b took place readily, giving the corresponding Dewar valence isomers, 10b and 11b.

SYNTHESIS AND PROPERTIES OF 14-SUBSTITUTED 1,4- THIAZINODIQUINOLINES

4,4′-Dichloro-3,3′-diquinolinyl sulfide 1 reacted with aryl-, heteroaryl- and alkylamines in MEDG or phenol to 14-substituted thiazino[2,3-c;6,5-c′]diquinolines 2, Reaction with ammonia, ammonium carbonate or benzylamine led to unsubstituted thiazine 2a, Alkylation of thiazine 2a with alkyl halides gave 14-alkyl-I,4- thiazinodiquinolines 2b, 2c and 2f, The nature of the 14-substituent has a significant effect on 1H NMR and MS spectral properties.

Revised structure for five acetophenones from Cynanchum taiwanianum

The structures of the acetophenones cynandione A-D and cynanchone A isolated from Cynanchum taiwanianum have been revised following re-examination of their NMR spectral properties.

Main Group Compounds as Amphoteric Ligands to Transition Metals. Synthesis and Molecular Structure of Cr(CO)5[PPh2CH2Ga(CH2CMe3)2·NMe3

The reactivities of the group 13 compounds, R2MCH2PPh2 and R2MPPh2, as amphoteric ligands to transition metals have been investigated. The ligands R2MCH2PPh2 (R = CH2CMe3, CH2SiMe3; M = Ga, In) reacted readily with Cr(CO)5NMe3 in benzene solution to form Cr(CO)5[PPh2CH2MR2·NMe3], whereas for ligands of the type R2MPPh2 (R = CH2CMe3, CH2SiMe3; M = Al, Ga, In), only the two aluminum compounds and (Me3CCH2)2GaPPh2 formed isolable products of the type Cr(CO)5[PPh2MR2·NMe3]. However, the gallium and indium ligands with (trimethylsilyl)methyl substituents (Me3SiCH2)2MPPh2 reacted with NEt4MT(CO)5Cl (MT = Cr, Mo, W) to form products of the type NEt4MT(CO)5[PPh2MR2Cl]. All new compounds were characterized by their physical properties, C and H analyses, and 1H and 31P NMR and IR spectral properties. The identity of NEt4Cr(CO)5[PPh2In(CH2SiMe3)2Cl] was further confirmed by the subsequent identification of products from reactions with anhydrous HCl and with MeI. In addition, Cr(CO)5[PPh2CH2Ga(CH2CMe3)2·NMe3] was characterized by an X-ray structural study.

Studies of the Selective O-Alkylation and Dealkylation of Flavonoids. XXI. A Convenient Method for Synthesizing 3,5,7-Trihydroxy-6,8-dimethoxyflavones and 5,7-Dihydroxy-3,6,8-trimethoxyflavones

Abstract The Friedel–Crafts acetylation with boron trifluoride was studied and it was found that 1-(2,4-dihydroxy-3,5,6-trimethoxyphenyl)ethanone was conveniently synthesized from 2,3,5,6-tetramethoxyphenyl acetate in a mixture of acetic anhydride and acetic acid. 1-[2-Hydroxy-3,5,6-trimethoxy-4-(methoxymethoxy)phenyl]ethanone was cyclized to 7-hydroxy-5,6,8-trimethoxyflavone by using the Baker–Venkataraman transformation. The 7-benzyl ether of the flavone was oxidized with dimethyldioxirane and then treated with a small amount of p-toluenesulfonic acid to give 7-benzyloxy-3-hydroxy-5,6,8-trimethoxyflavone, which was converted into the methyl ether and tosylate. The 5-methoxy group in the methyl ether or tosylate was selectively cleaved with anhydrous aluminum bromide in acetonitrile under mild conditions to give the corresponding 5-hydroxyflavones and the latter compound with a 3-tosyloxy group was smoothly converted into the 3,5-dihydroxyflavone by hydrolysis with potassium carbonate in methanol. The hydrogenolysis of the 7-benzyloxy-3,5-dihydroxyflavone and its 3-methyl ether afforded quantitatively 3,5,7-trihydroxy-6,8-dimethoxyflavone and its 3-methyl ether. The process was suitable as a general method for synthesizing 3,5,7-trihydroxy-6,8-dimethoxyflavones and their 3-methyl ethers and the six flavones were synthesized for the clarification of their 1H and 13C NMR, MS, and UV spectral properties.

Fullerene‐Acetylene Molecular Scaffolding: Chemistry of 2‐functionalized 1‐ethynylated C60, oxidative homocoupling, hexakis‐adduct formation, and attempted synthesis of C

AbstractOn the way to the fullerene‐acetylene hybrid carbon allotropes 2 and 6, the oxidative homocoupling of the 2‐functionalized 1‐ethynylated C60 derivatives 11, 12, 14, and 15 was investigated. Under Glaser‐Hay conditions, the two soluble dumbbell‐shaped bisfullerenes 17 and 18, with two C60 moieties linked by a buta‐1,3‐diynediyl bridge, were formed in 52 and 82% yield, respectively (Scheme 2). Cyclic‐voltammetric measurements revealed that there is no significant electronic communication between the two fullerene spheres via the buta‐1,3‐diynediyl linker. Removal of the 3,4,5,6‐tetrahydro‐2H‐pyran‐2‐yl (Thp) protecting groups in 18 gave in 80% yield the highly insoluble dumbbell 19 with methanol groups in the 2,2′‐positions of the buta‐1,3‐diynediyl‐bridged carbon spheres. Attempted conversion of 19 to the all‐carbon dianion 6 (C) via base‐induced elimination of formaldehyde was not successful presumably due to exo‐dig cyclization of the formed alkoxides. The occurrence of this cyclization under furan formation was proven for 2‐[4‐(trimethylsilyl)buta‐1,3‐diyn‐1‐yl][60]fullerene‐1‐methanol (21), a soluble model compound for 19 (Scheme 3). To compare the properties of ethynylated fullerene mono‐adducts to those of corresponding higher adducts, hexakis‐adducts 26 and 28 with an octahedral functionalization pattern resulting from all‐e (equatorial) additions were prepared by the reversible‐template method of Hirsch (Scheme 4). Reaction of the ethynylated mono‐adducts 25 or 13 with diethyl 2‐bromomalonate/1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in the presence of 1,9‐dimethylanthracene (DMA) as reversible template led to 26 and 28 in 28 and 22% yield, respectively. Preliminary experiments indicated a significant change in reactivity and NMR spectral properties of the fullerene addends with increasing degree of functionalization.

Modeling the Photosynthetic Water Oxidation Center: Chloride/Bromide Incorporation and Reversible Redox Processes in the Complexes Mn4O3X(OAc)3(dbm)3 (X = Cl, Br) and (pyH)3[Mn4O3Cl7(OAc)3

Synthetic procedures are described that allow conversion of [Mn4O2(OAc)6(py)2(dbm)2] (1, dbmH = dibenzoylmethane) to [Mn4O3X(OAc)3(dbm)3] (X = Cl, 2; X = Br, 3). Treatment of 1 with NBun4Cl in CH2Cl2 or hot MeCN leads to 2 in 5−8% and 35−43% yields (based on dbm), respectively. A higher yield (∼88%) is obtained by treating 1 with 4 equiv of Me3SiCl in CH2Cl2. An analogous procedure with 4 equiv of Me3SiBr in CH2Br2 gives 3 in 55% yield. Complexes 2 and 3 are isomorphous, monoclinic space group P21/n, T = −155 °C, Z = 4. For 2, a = 13.900(3), b = 22.038(5), and c = 16.518(5) Å and β = 107.80(1)°; for 3, a = 13.644(2), b = 22.190(4), and c = 16.548(3) Å, and β = 106.64(1)°. The structures were solved by direct methods (MULTAN78) and refined on F to R(Rw) values of 7.85 (7.38) and 7.37 (6.89)% using 2267 and 2809 unique reflections with F > 2.33σ(F) for 2 and 3, respectively. Treatment of [Mn3O(OAc)6(py)3](ClO4) in MeCN with Me3SiCl followed by addition of H2O and acetic acid results in crystallization of (pyH)3[Mn4O3Cl7(OAc)3]·2MeCN (4) in 75% yield (based on Mn). Complex 4 crystallizes in monoclinic space group C2/c with the following cell parameters at −157 °C: a = 37.420(5), b = 13.752(1), and c = 16.139(2) Å, β = 110.33(1), V = 7787.9 Å3, and Z = 8. The structure was solved by direct methods (MULTAN78) and refined on F to R(Rw) values of 5.74 (5.78)% using 2612 unique reflections with F > 3.0σ(F). The complexes possess a [Mn4(μ3-O)3(μ3-X)] distorted cubane core and a 3MnIII,MnIV trapped-valence oxidation-state description. Three AcO- groups bridge each MnIIIMnIV pair, and a chelating dbm- (2 and 3) or two Cl- ions (4) on each MnIII complete peripheral ligation. The pyridinium cations of 4 are involved in hydrogen-bonding interactions with the μ3-O2- and the terminal Cl- ions of the anion. Variable-temperature solid-state magnetic susceptibility studies show that the magnetic properties of 2 and 3 are very similar: μeff values steadily rise from ∼9 μB at room temperature to ∼10 μB at 30.0 K and then drop rapidly to ∼9.5 μB at 5 K. Fitting of the experimental data for the two complexes to the appropriate theoretical equation yield the following fitting parameters, in the format 2/3: J = J(MnIII···MnIV) = −28.4/−30.1 cm-1, J‘ = J(MnIII···MnIII) = +8.3/+7.4 cm-1, and g = 1.98/2.03. Both 2 and 3 have S = 9/2 ground states that are well-separated (∼180 cm-1) from an S = 7/2 first excited state. The ground state was confirmed by magnetization vs magnetic field studies at several fields and temperatures; fitting of the data allowed the zero-field splitting parameter D to be determined for both complexes. The magnetochemical properties of 4 are very similar to those of 2 and 3, and the fitting parameters were J = −29.1 cm-1, J‘ = +10.2 cm-1, and g = 1.97, giving an S = 9/2 ground state and showing that the hydrogen-bonding interactions of the μ3-O2- ions do not cause a significant change to the exchange parameters or to the electronic structure of the [Mn4O3Cl]6+ core. 1H NMR spectra of 2−4 in CDCl3 or CD3CN solution at ∼23 °C are similar and show that the Mn4 complexes retain their solid-state structure on dissolution in this solvent. X-band EPR spectra of 2 and 3 in CH2Cl2/toluene (1:1) glasses at 5 K are also extremely similar, with three main features at g = 11.0, 5.2, and 1.96. Cyclic voltammetry at 100 mV/s and differential pulse voltammetry at 5 mV/s show that both 2 and 3 support a reversible oxidation and two reductions, the first of which is reversible. The reversible processes are at 1.09/1.06 and −0.25/−0.21 V vs ferrocene and show that the [Mn4O3X] core can exist at three oxidation levels spanning the 4MnIII to 2MnIII, 2MnIV range. The combined results from 2 and 3 show that the identity of X has minimal influence on the resultant structures, magnetic properties, 1H NMR and EPR spectral properties, or the redox behavior. Such observations are of interest with regard to the ability of Br- to successfully substitute for Cl- at the photosynthetic water oxidation center and thus maintain the activity of the tetranuclear Mn aggregate toward oxygen evolution.

Synthesis and nitration of some thieno‐fused analogues of the benzo[a]quinolizinium cation

AbstractThree thieno‐fused analogues of benzo[a]quinolizinium (1), thieno[3,2‐a]‐ and thieno[2,3‐a]quinolizinium 4 and 5 and thiazolo[2,3‐a]isoquinolinium (6), were synthesized by photocyclization of 1‐(2‐thienylvinyl)pyridinium salts 9a and 9b and 3‐styrylthiazolium salt 9c, respectively. The nitration of the compounds 4, 5, and 6 occurred predominantly at positions 2, 3, and 7, respectively, while the nitro group was introduced into the 8‐ and 10‐positions of 1 in the ratio of 68:32. The nmr and uv spectral properties and reduction potentials of 4–6 were also compared with those of the parent compound 1.

Solution Studies of ReVO(anti-d-penicillaminato-N,S,O)(syn-d-penicillaminato-N,S)

The known Re(V)=O complex of d-penicillamine (d-penH4; the subscript indicates the number of dissociable protons) is isolated as a neutral form, ReO(d-penH3)(d-penH2) (1). The complex is six-coordinate with one CO2- bound trans to the oxo ligand, resulting in a cis-N2, cis-S2, trans-O2 geometry. One carboxyl group is anti and the other is syn to the oxo ligand; only the anti-pen CO2- can coordinate. For 1, in high-pH solutions, we have found unusual 1H NMR spectral properties that have led to the discovery of a facile oxo ligand exchange process. 1 was also studied by acid−base titration, which revealed that the neutral-pH form (I) was [ReO(syn-d-penH2-N,S)(anti-d-penH2-N,S,O)]-. Significant spectroscopic changes occurred at pH ∼11 and above. The two sets of pen 1H NMR signals observed at neutral pH decreased in intensity as the pH was raised, and several original signals shifted. Simultaneously, one new set of pen signals emerged. These new signals also shifted with increasing pH. These results indicate that (a) form I is in fast equilibration with a deprotonated form (I‘), (b) this mixture is in slow equilibrium with forms having different characteristics (II and II‘), and (c) II and II‘ rapidly interconvert. The II/II‘ component has one set of pen signals. Acid−base titrations indicated that the conversions from form I to forms I‘ and II each involve consumption of 1 mol of OH-. The nature of the forms present at different pH's was also examined by resonance Raman, UV−visible, and circular dichroism (CD) spectroscopy. These methods indicate OH- converts I into an equilibrium mixture: I‘ (by deprotonation of one NH) and II (by displacement of the axial carboxyl by axial hydroxo). An additional equivalent of OH- converted these two forms to II‘, which is probably a trans-dioxo species. Under conditions in which I‘, II, and II‘ coexisted, only the last two interconverted rapidly on the NMR time scale, since they interconverted by addition or loss of a proton. I‘ can convert to II only by a slower deligation process. II and II‘ were readily distinguished by the Raman experiment but not the longer time scale NMR experiments. Results in methanol supported this interpretation and only I, I‘, and IIMeOH were formed. IIMeOH differs from II in having an axial methoxo ligand. The methoxo ligand cannot be converted to an oxo ligand; thus, no II‘ was observed in methanol, and the NMR spectrum of IIMeOH has two sets of pen signals. The one set of pen signals for II in water can be explained by facile proton exchange interconverting the axial hydroxo/oxo and oxo/hydroxo sites.

Book Review: Phosphorus‐31 NMR Spectral Properties in Compound Characterization and Structural Analysis. Edited by L. D. Quin and J. G. Verkade

Book Review: Phosphorus‐31 NMR Spectral Properties in Compound Characterization and Structural Analysis. Edited by L. D. Quin and J. G. Verkade

Tris Buffer Reactivity with Low-Molecular-Weight Aldehydes: NMR Characterization of the Reactions of Glyceraldehyde-3-Phosphate

Tris (2-amino-2-hydroxymethylpropane-1,3-diol) reacts with aldehydes of low molecular weight in aqueous solutions to give products whose NMR spectral properties are inconsistent with the formation of the expected Schiff base. High-field 1H and 13C NMR spectra of a solution of Tris and glyceraldehyde 3-phosphate indicated initial formation of 2-(β-phosphoglycolyl)-4,4-bis(hydroxymethyl)1,3-oxazolidine, which was then converted to condensation products of Tris and methylglyoxal, accompanied by deuterium exchange when the solvent was 2H 2O. Acetaldehyde and benzaldehyde were used as model substrates which yielded more stable oxazolidines in their reactions with Tris.

Structural definition of early lysine and histidine adduction chemistry of 4-hydroxynonenal.

The lipid peroxidation product trans-4-hydroxy-2-nonenal (HNE) has been implicated in the covalent modification of low-density lipoproteins (LDL) thought to contribute to the over-accumulation of LDL in the arterial wall in the initial stages of atherosclerosis. Proposals for the exact structures of "early" protein side-chain modifications until now have been based on indirect evidence. In this paper, the structures of first-formed His- and Lys-based adducts were elucidated by correlating NMR spectral properties with those obtained on models with reduced chiral center content, in some cases following hydride reduction. In this manner, we could confirm unambiguously the structure of a HNE-His imidazole(N tau) Michael adduct, stabilized as a cyclic hemiacetal and isolated from a neutral aqueous 1:1 stoichiometry reaction mixture. In the case of Lys/amine reactivity, where an excess of amine is needed to avert HNE aldol condensation, the predominance of a 1:1 Michael adduct in homogeneous aqueous solution and a 1:2 Michael-Schiff base adduct under two-phase aqueous-organic conditions could be verified by isolation of the respective borohydride-reduced forms. The 1:2 adduct, shown to exist as the cyclic hemiaminal, could represent a stable lysine-based cross-link in certain protein microenvironments.

Acetonitrile complexes of diiridium Part 1. Isolation and characterization of the partially solvated cations [Ir 2(COD)(μ-form) 2(MeCN) 3] 2+ and [Ir 2(μ-form) 2(MeCN) 6] 2+ (COD = 1,5-cyclooctadiene, form = N, N′ -di- p-tolylformamidinate)

The partially solvated dinuclear complexes of the Ir 2 4+ core have been prepared from reactions of Ir 2(COD)(μ-form) 2 (O 2CCF 3) 2(H 2O) ( 1) with an alkylating reagent in acetonitrile. The compound [Ir 2(COD)(μ-form) 2(MeCN) 3][BF 4] 2 ( 2) is produced in essentially quantitative yields from reactions of 1 with an excess of Et 3OBF 4 in acetonitrile at room temperature whereas the thermal substitution product [Ir 2(μ-form) 2(MeCN) 6[BF 4] 2 ( 3) is isolated in ∼ 60% yield when the identical reaction is refluxed. Both compounds were fully characterized by IR and NMR spectroscopies, electrochemistry and X-ray crystallography. Single crystal X-ray data for 2·(CH 3) 2CO·(C 2H 5) 2O: monoclinic, P2 1/n, a = 19.534(6), b = 13.285(5), c = 22.113(4) A ̊ , β = 105.07(2)° , V = 5541(5) A ̊ 3, Z = 4, R = 0.074, R W = 0.107; 3: orthorhombic , Pbca, a = 21.670(6), b = 31.407(5), c = 14.543(6) A ̊ , V = 9898(9) A ̊ 3, Z = 8, R = 0.047, R W = 0.053 . The molecular structure of [Ir 2(COD)(μ-form) 2(MeCN) 3] 2+ is very similar to the parent trifluoroacetate complex and consists of an Ir-Ir unit bridged by two cis-tolylformamidinate groups, with one Ir atom ligated by a cyclooctadiene ligand in the equatorial plane and the other Ir center ligated by three MeCN molecules. The absence of an axial ligand on the Ir center bonded to the COD ligand and the short Ir-NCCH 3(axial) interaction of the other Ir atom (2.02(3) Å) support the formulation of the compound as a mixed-valence Ir(I)-Ir(III) species. The more symmetrical cation [Ir 2(μ-form) 2(MeCN) 6] 2+ is comprised of cis-tolyformamidinate ligands and six acetonitrile molecules that occupy four equatorial and two axial sites. In spite of the presence of two bridging ligands, the cations in 2 and 3 are considerably distorted from an eclipsed geometry with average torsional twist angles χ of 28 and 20°, respectively. The Ir-Ir distances of 2.717(2) Å for ( 2) and 2.601(1) Å for ( 3) are shorter than the corresponding metal-metal interaction in the parent complex Ir 2(COD)(μ-form) 2(O 2CCF 3) 2(H 2O) (2.774(1) Å) but are appreciably longer than the Ir-Ir bond length in the previously reported tetra-bridged molecule Ir 2(μ-form) 4 (2.524(3) Å). The 1H NMR spectral properties of the new compounds are in accord with retention of the solid state structures in solution ( C s symmetry for 2 and C 2 v symme in acetone at a glassy carbon electrode revealed quite different electronic properties for the two diiridium species, with 2 exhibiting behavior similar to the starting compound 1 which is in agreement with its description as a mixed-valence species. The syntheses and structures of the two new compounds in this study are discussed in light of their potential use as precursors to other metal-metal bonded Ir 2 4+ complexes including bridging carboxylase compounds and a fully solvated dinuclear cation.

Phosphorus-31 NMR Spectral Properties in Compound Characterization and Structural Analysis

Phosphorus-31 NMR Spectral Properties in Compound Characterization and Structural Analysis

Synthesis and characterization of rhenium metallocarboxylates

Reactions of a new metallocarboxylic acid, Cp*Re(CO)(NO)COOH (2), with Ph[sub 3]SnCl and Re(CO)[sub 4]-(PPh[sub 3])(F-BF[sub 3]) have provided the corresponding CO[sub 2]-bridged complexes Cp*Re(CO)(NO)(CO[sub 2])SnPh[sub 3] (3) and Cp*Re(CO)(NO)(CO[sub 2])Re(CO)[sub 3](PPh[sub 3]) (4), which have been structurally characterized. Complexes 3 and 4 exhibit different types of [mu][sub 2]-[eta][sup 3] bonding of the bridging CO[sub 2] ligand which can be correlated with the IR and [sup 13]C NMR spectral properties of the compounds. 15 refs., 2 figs.

Secondary structure and zinc ligation of human recombinant short-form stromelysin by multidimensional heteronuclear NMR.

Stromelysin-1, a member of the matrix metalloendoprotease family, is a zinc protease involved in the degradation of connective tissue in the extracellular matrix. As a step toward determining the structure of this protein, multidimensional heteronuclear NMR experiments have been applied to an inhibited truncated form of human stromelysin-1. Extensive 1H, 13C, and 15N sequential assignments have been obtained with a combination of three- and four-dimensional experiments. On the basis of sequential and short-range NOEs and 13C alpha chemical shifts, two helices have been delineated, spanning residues Asp-111 to Val-127 and Leu-195 to Ser-206. A third helix spanning residues Asp-238 to Gly-247 is characterized by sequential NOEs and 13C alpha chemical shifts, but not short-range NOEs. The lack of the latter NOEs suggests that this helix is either distorted or mobile. Similarly, sequential and interstrand NOEs and 13C alpha chemical shifts characterize a four-stranded beta-sheet with three parallel strands (Arg-100 to Ile-101, Ile-142 to Ala-147, Asp-177 to Asp-181) and one antiparallel strand (Ala-165 to Tyr-168). Two zinc sites have been identified in stromelysin [Salowe et al. (1992) Biochemistry 31, 4535-4540]. The NMR spectral properties, including chemical shift, pH dependence, and proton coupling of the imidazole nitrogens of six histidine residues (151, 166, 179, 201, 205, and 211), invariant in the matrix metalloendoprotease family, suggest that these residues are zinc ligands. NOE data indicate that these histidines form two clusters: one ligates the catalytic zinc (His-201, -205, and -211), and the other ligates a structural zinc (His-151, -166, and -179). Heteronuclear multiple quantum correlated spectra and specific labeling experiments indicate His-151, -179, -201, -205, and -211 are in the N delta 1H tautomer and His-166 is in the N epsilon 2H tautomer.

Sulfmyoglobin derived from deuterohemin reconstituted protein. 1. Structure of the initial complex based on the mechanism of formation of subsequent reaction products

The preparation, reactivity patterns, and 1 H NMR and optical spectral properties of the sulfmyoglobin, SMb, complex formed from equine myoglobin reconstituted with deuteroheme are investigated to shed light on the structure of the prosthetic group. The characteristic 1 H NMR spectral properties in both paramagnetic and diamagnetic derivatives of the initially formed green SMb show it to contain an iron chlorin with molecular/electronic structure very similar to that obtained with native protohemin (Chatfield, M. J.; La Mar, G. N.; Kauten, R. J. Biochemistry 1981, 27, 6939-6950), except that the deuterohemin SMb is significantly less stable with respect to reversion to starting material

Observation of the longst Fe–N(pyridine) bond in an FeIIN6chromophore. Crystal structure and1H nuclear magnetic resonance studies of [FeL22][ClO4]2[L2= 2-(3,5-dimethylpyrazol-1-ylmethyl)-6-(pyrazol-1-ylmethyl)pyridine

The X-ray structural and 1H NMR spectral properties of a bis(ligand) iron(II) complex of a tridentate pyridylpyrazole ligand L2[L2= 2-(3,5-dimethylpyrazol-1-ylmethyl)-6-(pyrazol-1-ylmethyl)pyridine] have been studied. The complex [FeL22][ClO4]2 crystallizes as yellow prisms in the monoclinic space group P21/n with a= 14.122(3), b= 13.612(3), c= 18.393(4)Å, β= 99.11(3)°, Z= 4, R= 0.0518 and R′= 0.0634 for 6464 observed reflections. The Fe atom is bound to six nitrogen atoms from two tridentate (N3) heterocyclic ligands. Considerable distortion is observed with the average Fe-N(pyridine) and Fe-N(pyrazole) distances being 2.274 and 2.173 Å respectively. These bond lengths are markedly longer than corresponding lengths for complexes of less sterically demanding ligands. As expected, the ligand molecules are not planar, the pyridyl and pyrazole rings being twisted relative to each other. The 3-methyl substituent induces a steric barrier to co-ordination and also greater inter-ligand repulsion and this is presumably responsible for the accessibility of the quintet state for FeII. The 1H NMR spectral measurements in CD3CN reveal that its solid-state structure is retained in solution.

Beiträge zur chemie organometallischer metallacyclischer nebengruppenmetallverbindungen: V. Synthese von Li 2[formula omitted]H 2) 2(Solv) x aus K[Ni(NPh 2) 3](THF) und LiCH 2CH 2CH 2CH 2Li; molekülstruktur von (Li(THF) 2) 2[formula omitted

A new synthetic route to Li 2Ni(C 4H 8) 2(Solv) x (Solv = diethylether, Et 2O, x = 1 ( 1); tetramethylethylendiamin, TMED, x = 2 ( 2); tetrahydrofuran, THF, 4 ( 3)) is described. (Li(THF) 2) 2Ni(C 4H 8) 2 ( 3) has been characterized by X-ray studies. The 1H and 13C NMR spectral properties of the metallacycles are reported.

Proton and carbon chemical shift assignment and dynamic investigation of the macrolide antibiotic tylosin

AbstractThe NMR spectral properties of the antibiotic tylosin were investigated. DQ‐COSY and HETCOR two‐dimensional spectra were used for the assignment of both the proton and protonated carbon signals. Selective (H)C‐NOE, were proposed for the controversial quaternary carbon assignments. The analysis of molecular motion in solution based on carbon spin–lattice relaxation rates shows that tylosin exhibits dynamics that are typical of each molecular moiety. A higher degree of free motion is observed with increasing distance from the macrolide nucleus.