Synthesis and characterization of novel intramolecularly O,C,O-coordinated heteroleptic organostannylenes and their tungstenpentacarbonyl complexes

The syntheses are reported of the novel heteroleptic organostannylenes [2,6-(ROCH₂)₂C₆H₃]SnCl (1, R = Me; 2, R = t-Bu) and of their tungstenpentacarbonyl complexes [2,6-(ROCH₂)₂C₆H₃](X)SnW(CO)₅ (3, X = Cl, R = Me; 4, X = Cl, R = t-Bu; 5, X = H, R = Me). The compounds were characterized by means of elemental analyses, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopies, electrospray mass spectrometry and in case of 3 and 4 also by single crystal X-ray diffraction analysis. For the two latter compounds the substituents bound at the ether oxygen atom control the strength of intramolecular O → Sn coordination. Thus, the O–Sn distances amount to 2.391(5)/2.389(5) (3) and 2.464(3)/2.513(3) Å (4).     

Synthesis of the (1S,2S)- and (1R,2S)-stereoisomers of the respective E- and Z-isomers of ethyl 4-[(2-hydroxycyclohexyl)methyl]phenoxy-3-methyl-2-butenoate using yeast whole cell bioreduction of the parent ketones

Saccharomyces cerevisiae, strain DBM 2115, was successfully employed in the reduction of the separated Z- and E-isomers of ethyl 4-[(2-oxocyclohexyl)methyl]phenoxy-3-methyl-2-butenoates 1 and 2, in order to prepare the (1S,2S)- and (1R,2S)-enantiomers of the corresponding ethyl 4-[(2-hydroxycyclohexyl)methyl]phenoxy-3-methyl-2-butenoates 3–6. The products were obtained with the required absolute configuration: (1S,2S)-3 (ee = 98%; yield 48%), (1R,2S)-4 (ee = >99%; yield 45%), (1S,2S)-5 (ee = 98.5%; yield 47%), and (1R,2S)-6 (ee = >99%; chemical yield 44%).     

Asymmetric reductions of ethyl 2-(benzamidomethyl)-3-oxobutanoate by yeasts

The stereoselective reduction of ethyl 2-(benzamidomethyl)-3-oxobutanoate 1 using yeasts was investigated among a restricted number (12) of yeasts. Kluyveromyces marxianus var. lactis CL69 diastereoselectively produced (2R,3S)-ethyl 2-(benzamidomethyl)-3-hydroxybutanoate 2, whereas Pichia glucozyma CBS 5766 gave (2S,3S)-2 as the major stereoisomer. The biotransformations were independently optimized for minimizing by-product formation and maximizing the diastereoselectivity. Under optimized conditions, K. marxianus var. lactis CL 69 gave the (2R,3S)-ethyl 2-(benzamidomethyl)-3-hydroxybutanoate 2 with ee > 99% and de = 98%, while P. glucozyma CBS 5766 allowed for the production of (2S,3S)-2 with ee > 99% and de = 86%.     

Synthesis,characterization and X-ray crystal structure determination of cyclopalladated [Csp2,N,N′]−, zwitterionic and chelated compounds in the reaction of 3,5-diphenyl-N-alkylaminopyrazole derived ligands with Pd(II)

The synthesis of two N-alkylaminopyrazole ligands, 1-[2-(diethylamino)ethyl]-3,5-diphenylpyrazole (L1) and 1-[2-(dioctylamino)ethyl]-3,5-diphenylpyrazole (L2), is reported. These ligands present, a priori, one pyrazole nitrogen and one amine nitrogen as potential donor atoms. However, in the reaction of the ligands (L1 and L2) with [PdCl₂(CH₃CN)₂] one of the C_phenyl atoms can also behave as a donor atom. As a result, we have obtained the formation of three different compounds for each one of the ligands: chelated ([PdCl₂(L)] L = L1 (1a), L2 (2a)), zwitterionic ([PdCl₃(LH)] LH = LH1 (1b), LH2 (2b)), and cyclopalladated compounds ([PdCl(LC)] (LC = LC1 (1c), LC2 (2c)). The solid-state structures for 1a, 1b and 1c were determined by single crystal X-ray diffraction methods. The potentially [C,N,N′]^? ligand is coordinated through the N_pz and the N_amino to the metal atom for 1a, through the N_pz for 1b, and through the N_pz, the N_amino and a C_phenyl for 1c.     

Crystallography and magnetism of 2-amido-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls

Two 2-Ar-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl radicals were synthesized (Ar = para-acetamidophenyl, and para-(tert-butyloxycarbonyl)aminophenyl, pAPNN, pBPNN) that incorporate amide-type NH moieties as potential hydrogen bonding sites. Both form hydrogen bonded cyclic dyads, but pAPNN exhibits spin pairing (2J/k = (−)5 K) due to a close, antiparallel nitroxide-nitroxide stacking contact, while pBPNN is essentially paramagnetic.     

Sterically hindered and completely arrested nitrogen inversion in pyrazolidines

Syntheses of trans-1,2-di-tert-butylpyrazolidine 1, d,l- and semi-meso-1,2-diisopropyl-3,5-dimethylpyrazolidines, 2a and 2b, respectively, have been developed. Activation parameters of the nitrogen inversion in 1 (ΔG^≠ = 123 kJ mol⁻¹ at 110 °C, ΔH^≠ = 114 kJ mol⁻¹, ΔS^≠ = −15 J K⁻¹ mol⁻¹) have been determined. The steric veto of the nitrogen inversion in 2a has been confirmed. Chemical transformations of 1 have been studied, and the crystal structures of 2a·picrate and 2b·HCl determined.     

Correlation between molecular structure and optical properties for the bis(2-(2-hydroxyphenyl)benzothiazolate) complexes

A series of methyl-substituted bis(2-(hydroxyphenyl)benzothiazolate)zinc derivatives [Zn(n-MeBTZ)₂, n = 3 (1a), 4 (1b), 5 (1c)] were synthesized to investigate the correlation between molecular structures and optical properties. The results indicate that the blue-emitting (λ_max = 470 nm) complex 1b is monomer with a higher PL quantum efficiency than complexes 1, 1a, 1c. Two green-emitting (λ_max = 507 nm and 499 nm) complexes 1a and 1c have special bi-molecular structures. The molecular structure for Zn(BTZ)₂ (complex 1) is dimer. Bilayer organic light-emitting devices were fabricated by using these complexes as emitting layer. The maximum emission wavelengths of the devices are in the range of 501–553 nm. The devices show turn-on voltages at 9.2, 12.7, 2.3 and 10.7 V for complex 1, 1a, 1b, and 1c, respectively. In particular, the device with complex 1b shows a higher brightness than the other complexes under the same conditions.     

Hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands: Imidazole and oxazole ring Lewis basicity,Ni(II)/Pd(II) complex structures and spectra

Fourteen new organic molecules A1–A4, B1–B5, C1–C4 and D and a series of transition metal(II) complexes (Ni1–Ni9 and Pd1–Pd2b) were synthesized and studied in order to characterize the hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands (A1–A4 = 2-R²-6-(4,5-diphenyl-1R¹-imidazol-2-yl)pyridines, R¹ = H or CH₃, R² = H or CH₃; B1–B5 = 1-R²-2-(pyridin-2-yl)-1R¹-phenanthro[9,10-d]imidazoles/oxazoles, R¹ = H or CH₃, R² = H or CH₃; C1–C4 = 2-(6-R²-pyridin-2-yl)-1H-imidazo/oxazo[4,5-f][1,10]phenanthrolines, R² = H or CH₃; D = 2-mesityl-1H-imidazo[4,5-f][1,10]phenanthroline). They were also used to study the substituent effects on the donor strengths as well as the coordination chemistries of the imidazole/oxazole fragments of the hemilabile ligands.All the observed protonation–deprotonation processes found within pH 1–14 media pertain to the imidazole or oxazole rings rather than the pyridyl Lewis bases. The donor characteristics of the imidazole/oxazole ring can be estimated by spectroscopic methods regardless of the presence of other strong N donor fragments. The oxazoles possessed notably lower donor strengths than the imidazoles. The electron-withdrawing influence and capacity to hinder the azole base donor strength of 4,5-azole substituents were found to be in the order phenanthrenyl (B series) > 4,5-diphenyl (A series) > phenanthrolinyl (C series). An X-ray structure of Ni5b gave evidence for solvent induced ligand reconstitution while the structure of Pd2b provided evidence for solvent induced metal–ligand bond disconnection.Interestingly, alkylation of 1H-imidazoles did not necessarily produce the anticipated push of electron density to the donor nitrogen. Furthermore, substituents on the 4,5-carbons of the azole ring were more important for tuning donor strength of the azole base. DFT calculations were employed to investigate the observed trends. It is believed that the information provided on substituent effects and trends in this family of ligands will be useful in the rational design and synthesis of desired azole-containing chelate ligands, tuning of donor properties and application of this family of ligands in inorganic architectural designs, template-directed coordination polymer preparations, mixed-ligand inorganic self-assemblies, etc.     

Synthesis of rigid and C2-symmetric 18-crown-6 type macrocycles bearing diamide–diester groups: enantiomeric recognition for α-(1-naphthyl)ethylammonium perchlorate salts

A series of rigid and chiral C₂-symmetric 18-crown-6 type macrocycles (S,S)-4, (S,S)-5, (S,S)-6 and (R,R)-2 bearing diamide–ester groups were synthesized. The binding properties of these macrocycles were examined for α-(1-naphthyl)ethylammonium perchlorates salts by an ¹H NMR titration method. Taking into account the host employed, important differences were observed in the K_a values of (R)- and (S)-enantiomers of guests for macrocycles (S,S)-4 and (S,S)-6, K_S/K_R = 3.6, and K_S/K_R = 0.1 (K_R/K_S = 10.3) ΔΔG = 3.19 and ΔΔG = ?5.77 kJ mol^?1, respectively. The results indicated excellent enantioselectivity of macrocyclic (S,S)-6 towards the enantiomers of α-(1-naphthyl)ethylammonium perchlorate salts.     

Design,synthesis, and fungicidal activity of novel 1,3,4-oxadiazole derivatives

Employing the intermediate derivatization method (IDM), a series of 1,3,4-oxadiazole derivatives containing arylpyrazoloxyl moiety were designed and synthesized. In vitro bioassays showed that these compounds have moderate to significant fungicidal activity against rice sheath blight and sorghum anthracnose. Furthermore, compound 20 is a promising fungicide for further development.     

Reactivity of intramolecularly coordinated aluminum compounds to R3EOH (E = Sn,Si). Remarkable migration of N,C,N and O,C,O pincer ligands

The reaction of organoaluminum compounds containing O,C,O or N,C,N chelating (so called pincer) ligands [2,6-(YCH₂)₂C₆H₃]AlⁱBu₂ (Y = MeO 1, ^tBuO 2, Me₂N 3) with R₃SnOH (R = Ph or Me) gives tetraorganotin complexes [2,6-(YCH₂)₂C₆H₃]SnR₃ (Y = MeO, R = Ph 4, Y = MeO, R = Me 5; Y = ^tBuO, R = Ph 6, Y = ^tBuO, R = Me 7; Y = Me₂N, R = Ph 8, Y = Me₂N, R = Me 9) as the result of migration of O,C,O or N,C,N pincer ligands from aluminum to tin atom. Reaction of 1 and 2 with (ⁿBu₃Sn)₂O proceeded in similar fashion resulting in 10 and 11 ([2,6-(YCH₂)₂C₆H₃]SnⁿBu₃, Y = MeO 10; Y = ^tBuO 11) in mixture with ⁿBu₃SnⁱBu. The reaction 1 and 3 with 2 equiv. of Ph₃SiOH followed another reaction path and ([2,6-(YCH₂)₂C₆H₃]Al(OSiPh₃)₂, Y = MeO 12, Me₂N 13) were observed as the products of alkane elimination. The organotin derivatives 4–11 were characterized by the help of elemental analysis, ESI-MS technique, ¹H, ¹³C, ¹¹⁹Sn NMR spectroscopy and in the case 6 and 8 by single crystal X-ray diffraction (XRD). Compounds 12 and 13 were identified using elemental analysis,¹H, ¹³C, ²⁹Si NMR and IR spectroscopy.     

The reaction of amidinato(pyridine) complexes of molybdenum and tungsten with triethylborane adduct of N-heterocyclic carbene (NHC · BEt3): Investigation on the reactivity of NHC · BEt3 as carbene precursor toward transition metal complexes

The reaction of triethylborane adduct of N-heterocyclic carbene, NHC · BEt₃, (NHC = IⁱPr = 1,3-diisopropylimidazol-2-ylidene (IⁱPr · BEt₃; 1a), NHC = IMes = 1,3-dimesitylimidazol-2-ylidene (IMes · BEt₃; 1b)), which was prepared by the reaction of the corresponding imidazolium salt with one equivalent of LiBEt₃H, with amidinato(pyridine) complex, [M(η³-allyl){η²-(NPh)₂CH}(CO)₂(NC₅H₅)] (M = Mo; 2-Mo M = W; 2-W), was investigated. The reaction of compound 1 with complex 2 under toluene-reflux conditions resulted in the formation of carbene complex [M(η³-allyl){η²-(NPh)₂CH}(CO)₂(NHC)] (M = Mo, NHC = IⁱPr; 3a-Mo, M = Mo, NHC = IMes; 3b-Mo, M = W, NHC = IⁱPr; 3a-W, M = W, NHC = IMes; 3b-W). These complexes were characterized spectroscopically as well as by X-ray analyses. Complex 3a-Mo was formed in various solvents such as 1,2-dimethoxyethane (DME), 1,2-dichloroethane, and acetonitrile under refluxing conditions for 3 h. In toluene, 3a-Mo was obtained in a good yield by heating at 70 °C for only 20 min. Employment of NHC · BEt₃ (1) was found to afford convenient route for the introduction of the carbene ligand to the transition metal complexes.     

Two new C-glycosylflavones from Mimosa pudica

Two new C-glycosylflavones were isolated from the whole plant of Mimosa pudica,and their structures were determined as 6,7,3′,4′-tetrahydroxyl-8-C-[α-L-rhamnopyranosyl-(1→2)]-β-D-glucopyranosyl flavone(1),5,7,3′,4′-tetrahydroxy-8-C[β-D- apiose-(1→4)]-β-D-glycopyranosyl flavone (2).Their structures elucidated by chemical and spectroscopic analysis including IR,MS,1D and 2D NMR spectra.     

Do lipases also catalyse the ring cleavage of inactivated cyclic trans-β-lactams?

Twelve-membered cyclic cis- and trans-β-lactams 1b and 2b and the corresponding cyclic cis- and trans-β-amino acid enantiomers, 1a, 1c and 2a, 2c were prepared through the CAL-B-catalysed enantioselective ring cleavage of racemic cis-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-1, and trans-13-azabicyclo[10.2.0]tetradecan-14-one, (±)-2. High enantioselectivities (E >200) were observed for the ring opening of both the cis- and trans-β-lactams when the Lipolase-catalysed reactions were performed with 0.5 equiv of H₂O in i-Pr₂O at 70 °C. The resolved β-lactams 1b and 2b (yield ⩾47%) and β-amino acids 1a and 2a (yield ⩾32%) could be easily separated.     

Hybrid inorganic–organic frameworks containing magnesium: Synthesis and structures of magnesium squarate,diglycolate, and glutarate,and potassium magnesium cyclobutanetetracarboxylate

Four new magnesium containing metal–organic hybrid compounds have been synthesized in an effort to prepare low-density materials for hydrogen storage. The compounds were prepared hydrothermally and characterized using single crystal X-ray diffraction. Three of these compounds are analogs of known transition metal structures with squarate (I, Pn-3n, a = 16.276(5) Å), diglycolate (II, P2₁2₁2₁, a = 6.860(1) Å, b = 9.993(1) Å, c = 10.884(1) Å, R₁ = 0.0341), and glutarate (III, R-3, a = 10.744(2) Å, c = 28.677(5) Å, R₁ = 0.0554) ligands; the fourth is a novel structure using cyclobutanetetracarboxylate (IV, Pccn, a = 9.382(1) Å, b = 14.410(2) Å, c = 8.725(1) Å, R₁ = 0.0465) which contains potassium as well as magnesium cations.     

Dialkyl- and diaryl-platinum(II) complexes with secondary phosphines: Preparation,structure and thermal reaction giving the metallopolymer

Alkyl and arylplatinum complexes with 1,5-cyclooctadiene ligand, [PtR₂(cod)] (R = Me, Ph, C₆H₄-p-CF₃, C₆F₅), react with secondary phosphines, PHR′₂ (R′ = i-Bu, t-Bu, Ph), to afford the mononuclear platinum complexes, cis-[PtR₂(PHR′₂)₂] (1a: R = Me, R′ = i-Bu; 1b: R = Me, R′ = t-Bu; 1c: R = Me, R′ = Ph; 2a: R = Ph, R′ = i-Bu; 2b: R = Ph, R′ = t-Bu; 2c: R = R′ = Ph; 3a: R = C₆H₄-p-CF₃, R′ = i-Bu; 3b: R = C₆H₄-p-CF₃, R′ = t-Bu; 3c: R = C₆H₄-p-CF₃, R′ = Ph; 4a: R = C₆F₅, R′ = i-Bu; 4c: R = C₆F₅, R′ = Ph) in 81–98% yields. Molecular structures of the complexes except for 1a, 1c and 2a were determined by X-ray crystallography. Complex 1b has a square-planar structure with Pt–C(methyl) bonds of 2.083(8) and 2.109(8) Å, while the Pt–C(aryl) bonds of 2b–c, 3a–c, 4a and 4c (2.055(1)–2.073(8) Å) are shorter than them. Thermal decomposition of 1b, 2a–c, and 3a–c releases methane, biphenyl or 4,4′-bis(trifluoromethyl)biphenyl as the organic products, which are characterized by NMR spectroscopy. The solid product of the thermal reactions of 2b and 2c were characterized as the metallopolymers formulated as [Pt(PR′₂)₂]_n (5b: R′ = ^tBu; 5c: R′ = Ph), based on the solid-state NMR and elemental analyses.     

Furostanol saponins with inhibitory action against COX-2 production from Tupistra chinensis rhizomes

Two furostanol saponins were obtained from the n-butanol fraction of methanol extract from Tupistra chinensis rhizomes,a folk medicine of Shennongjia Forest District of Hubei Province.Their structures were determined as (25S)-26-O-(β-D-glucopyranosyl)- furost-1β,3β,22α,26-tetrol-3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glucopyranoside (1) and (25R)- 26-O-(β-D-glucopyranosyl)-furost-1β,3β22α,26-tetrol 3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glu- copyranoside (2),on basis of chemical and spectroscopic evidences.1 and 2 displayed marked inhibitory action towards COX-2 production in macrophages of the rat abdomen induced by LPS at 20μg/mL.     

Two new saponins from Anemarrhena asphodeloides Bge.

Two new saponins 3-O-β-D-glucopyranosyl (1→2)-β-D-mannopyranosyl sarsasapogenin, named timosaponin A IV(1) and (5β, 25S)-26-O-β-D-glucopyranosyl-furost-20(22)-en-3,26-diol-3-O-β-D-glucopyranosyl (1→4) glucopyranosyl (1→2)-β-D-galacopyranoside, named timosaponin B IV(2), were isolated by silica gel column chromatography and preparative HPLC from Anemarrhena asphodeloides Bge. Their structures were elucidated by chemical characters and spectroscopic analysis.     

Tuning the electronic properties of Fe2(μ-arenedithiolate)(CO)6−n(PMe3)n (n = 0, 2) complexes related to the [Fe–Fe]-hydrogenase active site

Complexes [Fe₂(μ-S₂Ar)(CO)₆] (S₂Ar) = benzene-1,2-dithiolate (1a) toluene-3,4-dithiolate (2a), 3,6-dichloro-1,2-benzenedithiolate (3a), quinoxaline-2,3-dithiolate (7a) have been prepared to investigate the electronic effect that different bridging arenedithiolate ligands have on the appended Fe₂(CO)₆ sites. Dinuclear complexes [Fe₂(μ-S₂Ar)(CO)₄(PMe₃)₂] (1–3,7)b and mononuclear complexes [Fe(S₂Ar)(CO)₂(PMe₃)₂] (1–3,7)c were synthesized from their parent hexacarbonyl complexes (1–3,7)a. IR spectroscopic, crystallographic and electrochemical analyses show that an increase of the electron-withdrawing character (where quinoxaline-2,3-dithiolate > 3,6-dichloro-1,2-benzenedithiolate > 1,2-benzenedithiolate ≥ toluene-3,4-dithiolate) of the bridging ligand leads to a decreased electron density at the iron centers, which yield a milder reduction potential and higher eCO stretching frequencies. This effect is coherent for all of the investigated complexes. Electrocatalytic proton reduction by complex 3a (with trifluoromethanesulfonic acid) was evidenced by cyclic voltammetry. As a result of the milder reduction potential of 3a itself, proton reduction that is promoted by 3a proceeds at a potential that is milder than that for the 1a-catalyzed process.     

Magnetic interactions in p-phenylene-bis(nitronyl nitroxide) biradicals with large torsion angles

We have designed and synthesized new biradicals of p-phenylene-bis(nitronyl nitroxide) substituted with two methoxy groups at 2,3- (2) and 2,5-positions (3). A parent biradical p-phenylene-bis(nitronyl nitroxide) (1) has intramolecular antiferromagnetic exchange interaction of 2J/k_B = −104 K ∼ −106 K with a torsion angle of 28.5° between the phenyl and the imidazole rings of nitronyl nitroxide. X-ray crystal structure analysis shows that the bulky substituents in 2 and 3 give large torsion angles of 65–70°. The larger torsion angles should weaken the magnitude of intramolecular exchange interactions, which is attributed to a decrease in π-conjugation over the p-phenylene and the radical groups. Magnetic susceptibility measurements indicate that the intramolecular exchange interactions in 2 and 3 are severely weakened to about 6% of that in 1, 2J/k_B = −6 K ∼ −8 K. The relation between the torsion angle and the intramolecular exchange interaction is consistent with DFT calculations. The ground-state singlet biradicals with suppressed intramolecular exchange interactions can be a building block for exotic exchange-coupled spin systems as predicted in our theoretical studies.