Trapping unstable terminal M-O multiple bonds of monocyclopentadienyl niobium and tantalum complexes with Lewis acids

Hydrolysis of [NbCp'Cl(4)] (Cp' = η(5)-C(5)H(4)SiMe(3)) with the water adduct H(2)O·B(C(6)F(5))(3) afforded the oxo-borane compound [NbCp'Cl(2){O·B(C(6)F(5))(3)}] (2a). This compound reacted with [MgBz(2)(THF)(2)] giving [NbCp'Bz(2){O·B(C(6)F(5))(3)}] (2b), whereas [NbCp'Me(2){O·B(C(6)F(5))(3)}] (2c) was obtained from the reaction of [NbCp'Me(4)] with H(2)O·B(C(6)F(5))(3). Addition of Al(C(6)F(5))(3) to solutions containing the oxo-borane compounds [MCp(R)X(2){O·B(C(6)F(5))(3)}] (M = Ta, Cp(R) = η(5)-C(5)Me(5) (Cp*), X = Cl 1a, Bz 1b, Me 1c; M = Nb, Cp(R) = Cp', X = Cl 2a) afforded the oxo-alane complexes [MCp(R)X(2){O·Al(C(6)F(5))(3)}] (M = Ta, Cp(R) = Cp*, X = Cl 3a, Bz 3b, Me 3c; M = Nb, Cp(R) = Cp', X = Cl 4a), releasing B(C(6)F(5))(3). Compound 3a was also obtained by addition of Al(C(6)F(5))(3) to the dinuclear μ-oxo compound [TaCp*Cl(2)(μ-O)](2), meanwhile addition of the water adduct H(2)O·Al(C(6)F(5))(3) to [TaCp*Me(4)] gave complex 3c. The structure of 2a and 3a was obtained by X-ray diffraction studies. Density functional theory (DFT) calculations were carried out to further understand these types of oxo compounds.     

Fragmentation reactions of alkylphenylammonium ions

The fragmentation reactions of a variety of alkylphenylammonium ions, C(6)H(5)NH(3 -n)R(n)(+) (n >/= 1, R = CH(3), C(2)H(5), i-C(3)H(7), n-C(4)H(9)) were studied by energy-resolved mass spectrometry. Ionization was by fast atom bombardment (FAB) or electrospray ionization. Energy-resolved fragmentation data were obtained by low-energy collision-induced dissociation (CID) in the quadrupole cell of a hybrid sector/quadrupole instrument following FAB ionization and by cone-voltage CID in the interface region of the electrospray/quadrupole instrument. A comparison of the two methods of obtaining energy-resolved data showed that very similar results are obtained by the two methods. The fragmentation reactions of the alkylphenylammonium ions are rationalized in terms of competitive formation of an [R(+)-NC(6)H(5)H(3-n)R(n-1)] complex or a [C(6)H(5)H(3-n)R(n-1)N(+.)-(.)R] complex. The former complex fragments by internal proton transfer to yield C(6)H(5)H(3 -n)R(n -1)NH(+) and [R -H] whereas the latter complex fragments to form C(6)H(5)H(3 -n)R(n -1)N(+) and an alkyl radical. Alkane elimination, which is very prominent for tetraalkylammonium ions, most likely involves sequential elimination of an alkyl radical and either an H atom or an alkyl radical for the phenyl-substituted ammonium ions. Copyright 1999 John Wiley & Sons, Ltd.     

Supramolecular assemblies of sulfonatocalixarenes with phenanthroline: factors governing capsule formation versus bilayer arrangements

Four crystalline complexes were prepared by the inclusion complexation of the 1,10-phenanthrolinium ion (Phen) with p-sulfonatothiacalix[4]arene (TCAS) (2 from a solution at pH 1-2 and 4 from 1 M HCl) and with p-sulfonatocalix[5]arene (C5AS) (3 from a solution at pH 1-2 and 5 from 1 M HCl) upon varying the acidity of the solution. By combining the results obtained for complexes 2-5 with those for our previously reported complex (1), p-sulfonatocalix[4]arene (C4AS) complexed to Phen, it was revealed that p-sulfonatocalixarenes (CASs) form "bis-molecular" capsules (1, 2, and 3) around Phen at pH 1-2, whereas complexes 4 and 5 display distinct host-guest inclusion behavior at higher acid concentrations. The degree of compactness of the capsules increases with the enlargement of the calixarene cavity, which is affected significantly by both the penetration depth of Phen and the structure of the Phen dimer. Furthermore, the complexation behavior of TCAS/C5AS with Phen in 1 M DCl was investigated by using NMR spectroscopy, and was discussed in comparison with the previously reported results obtained from solutions at pH 2.0.     

The synthesis and characterisation of Sn(IV) complexes of 2,6-pyridine dicarboxylate--the molecular structure of divinyltin(IV) derivative

A series of organotin(IV) derivatives were obtained employing 2,6-pyridinedicarboxylate as ligand: [{SnBu3(OOC)2C5H3N}n] (1), [SnBuCl(OOC)2C5H3N] (2) and [Sn(CHCH2)2(OOC)2C5H3N] (3). They were fully characterised by multinuclear NMR [1H, 13C{1H}, and 119Sn{1H}], IR spectroscopies and elemental analysis. In addition suitable crystals of (3) have shown a dimmeric arrangement by X-ray crystallographic studies, held together by Sn-O intermolecular interactions which persists in solution. The crystal packing shows hydrogen bonds joining the dimmers, forming two infinite one-dimensional chain. Each monomer comprises a Sn(IV) centre bonded to a pyridinecarboxylate-containing ring, through both nitrogen and oxygen donor atoms. It is also co-ordinated by a water molecule and two vinyl groups.     

A simple approach to coordination compounds of the pentacyanocyclopentadienide anion

Deprotonation of [Et(3)NH][C(5)(CN)(5)] with metal bases provides a very simple approach to coordination compounds containing the pentacyanocyclopentadienide anion [C(5)(CN)(5)](-) (1). The three-dimensional polymer [Na(thf)(1.5)(1)](∞) and the molecular dimer [{(tmeda)(2)Na(1)}(2)] are obtained by reaction of this precursor with NaH in the presence of thf or tmeda (Me(2)NCH(2)CH(2)NMe(2)). Their single-crystal X-ray structures both reveal σ-bonded C≡N-Na arrangements and π stacking between [C(5)(CN)(5)](-) ions. DFT calculations on the [C(5)(CN)(5)](-) ion have been used to investigate the structures and bonding in [Na(thf)(1.5)(1)](∞) and [{(tmeda)(2)Na(1)}(2)]. The absence of π bonding of the metal ions in both complexes is due to dispersion of the negative charge from the C(5) ring unit to the C[triple chemical bond]N groups in the [C(5)(CN)(5)](-) ion, making the coordination chemistry of this anion distinctly different from that of cyclopentadienide C(5)H(5)(-).     

Conformational stability of cyclobutanol from temperature dependent infrared spectra of xenon solutions, r0 structural parameters, ab initio calculations and vibrational assignment

Variable temperature (-55 to -100 degrees C) studies of the infrared spectra (4000-400 cm(-1)) of cyclobutanol, c-C4H7OH dissolved in liquid xenon have been carried out. The infrared spectrum (4000-100 cm(-1)) of the gas has also been recorded. From these data two of the four possible stable conformers have been confidently identified and their order of stabilities has been experimentally determined where the first indicator is for the position of attachment of the hydroxyl group on the bent cyclobutyl ring (Eq=equatorial or Ax=axial) and the second one (t=trans, g=gauche) is the relative position of the hydroxyl rotor, i.e. rotation around the ring C-O bond. The enthalpy difference between the most stable Eq-t conformer and the second most stable rotamer, Eq-g, has been determined to be 200+/-50 cm(-1) (2.39+/-0.60 kJ/mol). This experimentally determined order is consistent with the order of stability predicted by ab initio calculations Eq-t>Eq-g>Ax-g>Ax-t. Evidence was obtained for the third conformer Ax-g which is predicted by ab initio calculations to be less stable by more than 650cm(-1) than the Eq-t form. The percentage of each conformer at ambient temperature is estimated to be Eq-t (50%), Eq-g (47%) and Ax-g (3%). The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for all of the conformers from MP2(full)/6-31G(d) ab initio calculations. The optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing several different basis sets up to MP2(full)/aug-cc-pVTZ and from density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants for the Eq-t conformer combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained. The determined heavy atom structural parameters for the Eq-t conformer are: the distances C1-C4=1.547(5) angstroms, C4-C6=1.552(5)angstroms, C-O=1.416(5) angstroms and angles angleC6C4C1=86.6(5) degrees , angleC4C1C5=88.9(5) degrees and angleC6C5C1C4=22.8(5) degrees . The results are discussed and compared to the corresponding properties of some similar molecules.     

Hydrolytic metal-mediated coupling of dialkylcyanamides at a Pt(IV) center giving a new family of diimino ligands

Addition of excess R(2)NCN to an aqueous solution of K(2)[PtCl(4)] led to the precipitation of [PtCl(2)(NCNR(2))(2)] (R(2) = Me(2) 1; Et(2) 2; C(5)H(10) 3; C(4)H(8)O, 4) in a cis/trans isomeric ratio which depends on temperature. Pure isomers cis-1-3 and trans-1-3 were separated by column chromatography on SiO(2), while trans-4 was obtained by recrystallization. Complexes cis-1-3 isomerize to trans-1-3 on heating in the solid phase at 110 degrees C; trans-1 has been characterized by X-ray crystallography. Chlorination of the platinum(II) complexes cis-1-3 and trans-1-4 gives the appropriate platinum(IV) complexes [PtCl(4)(NCNR(2))(2)] (cis-5-7 and trans-5-8). The compound cis-6 was also obtained by treatment of [PtCl(4)(NCMe)(2)] with neat Et(2)NCN. The platinum(IV) complex trans-[PtCl(4)(NCNMe(2))(2)] (trans-5) in a mixture of undried Et(2)O and CH(2)Cl(2) undergoes facile hydrolysis to give trans-[PtCl(4)[(H)=C(NMe(2))OH](2)] (9; X-ray structure has been determined). The hydrolysis went to another direction with the cis-[PtCl(4)(NCNR(2))(2)] (cis-5-7) which were converted to the metallacycles [PtCl(4)[NH=C(NR(2))OC(NR(2))=NH]] (11-13) due to the unprecedented hydrolytic coupling of the two adjacent dialkylcyanamide ligands giving a novel (for both coordination and organic chemistry) diimino linkage. Compounds 11-13 and also 14 (R(2) = C(4)H(8)O) were alternatively obtained by the reaction between cis-[PtCl(4)(MeCN)(2)] and neat undried NCNR(2). The structures of complexes 11, 13, and 14 were determined by X-ray single-crystal diffraction. All the platinum compounds were additionally characterized by elemental analyses, FAB mass-spectrometry, and IR and (1)H and (13)C[(1)H] NMR spectroscopies.     

Carbon-carbon bond formation of alkenylphosphonates by aldehyde insertion into zirconacycle phosphonates

Ethyl 1-butynylphosphonate reacts with Cp(2)ZrCl(2)/2n-BuLi to give a three-membered zirconacycle that readily inserts aldehydes. Hydrolysis of the intermediate five-membered zirconacycles leads to two products, 4 and 5. In the major product, 5, the aldehyde inserts into C2 of the zirconacycle, while in the minor product, 4, the aldehyde inserts into C1. Products 5 are obtained in 38-75% isolated yields. Products 4 are obtained in approximately 1-12%. Essentially, only compounds 5 are produced with ortho-substituted aldehydes. The regio- and stereochemistry of 4 and 5 were determined by (3)J(PH), (2)J(PC2), and (3)J(PC3) coupling constants.     

Ability of a Au(III)-N unit to bond two aurophilically interacting gold(I) centers

The monohapto neutral 2-(diphenylphosphino)aniline (PNH(2)) complexes [Au(C(6)F(5))(2)X(PNH(2))] (X = C(6)F(5) (1), Cl (2)) have been obtained from [Au(C(6)F(5))(3)(tht)] or [Au(C(6)F(5))(2)(micro-Cl)](2) and PNH(2), and the cationic [Au(C(6)F(5))(2)(PNH(2))]ClO(4) (3) has been similarly prepared from [Au(C(6)F(5))(2)(OEt(2))(2)]ClO(4) and PNH(2) or from 2 and AgClO(4). The neutral amido complex [Au(C(6)F(5))(2)(PNH)] (4) can be obtained by deprotonation of 3 with PPN(acac) (acac = acetylacetonate) or by treatment of the chloro complex 2 with Tl(acac). It reacts with [Ag(OClO(3))(PPh(3))] or [Au(OClO(3))(PPh(3))] to give the dinuclear species [Au(C(6)F(5))(2)[PNH(MPPh(3))]]ClO(4) (M = Ag (5), Au (6)). The latter can also be obtained by reaction of equimolar amounts of 3 and [Au(acac)(PPh(3))]; when the molar ratio of the same reagents is 1:2, the trinuclear cationic complex [Au(C(6)F(5))(2)[PN(AuPPh(3))(2)]]ClO(4) (7) is obtained. The crystal structures of complexes 2-4 and 7 have been established by X-ray crystallography; the last-mentioned displays an unusual Au(I)-Au(III) interaction.     

Frustrated beta-chloride elimination. Selective arene alkylation by alpha-chloronorbornene catalyzed by electrophilic metallocenium ion pairs

Single-site polymerization catalysts generated in situ via activation of Cp*MMe(3) (Cp* = C(5)Me(5); M = Ti, Zr), (CGC)MMe(2) (CGC = C(5)Me(4)SiMe(2)NBu(t)(); M = Ti, Zr), and Cp(2)ZrMe(2) with Ph(3)C(+)B(C(6)F(5))(4)(-) catalyze alkylation of aromatic molecules (benzene, toluene) with alpha-chloronorbornene at room temperature, to regioselectively afford the 1:1 addition products exo-1-chloro-2-arylnorbornane (aryl = C(6)H(5) (1a), C(6)H(4)CH(3) (1b)) in good yields. Analogous deuterium-labeled products exo-1-chloro-2-aryl-d(n)-norbornane-7-d(1) (aryl-d(n) = C(6)D(5) (1a-d(6)), C(6)D(4)CD(3) (1b-d(8))) are obtained via catalytic arylation of alpha-chloronorbornene in either benzene-d(6) or toluene-d(8). Isolated ion-pair complexes such as (CGC)ZrMe(toluene)(+)B(C(6)F(5))(4)(-) and Cp(2)ThMe(+)B(C(6)F(5))(4)(-) also catalyze the reaction of alpha-chloronorbornene in toluene-d(8) to give 1b-d(8) in good yields, respectively. Small quantities of the corresponding bis(1-chloronorbornyl)aromatics 2 are also obtained from preparative-scale reactions. These reactions exhibit turnover frequencies exceeding 120 h(-1) (for the Cp*TiMe(3)/Ph(3)C(+)B(C(6)F(5))(4)(-)-catalyzed system), and chlorine-free products are not observed. Compounds 1 and 2 were characterized by (1)H, (2)H, (13)C, and 2D NMR, GC-MS, and elemental analysis. The aryl group exo-stereochemistry in 1a and 1b is established using (1)H-(1)H COSY, (1)H-(13)C HMBC, and (1)H-(1)H NOESY NMR, and is further corroborated by X-ray analysis of the product 1,4-bis(exo-1-chloro-2-norbornyl)benzene (2a). Control experiments and reactivity studies on each component step suggest a mechanism involving participitation of the metal electrophiles in the catalytic cycle.     

Stereoselective Synthesis of 8,12-Furanoeudesmanes from Santonin. Absolute Stereochemistry of Natural Furanoeudesma-1,3-diene and Tubipofurane

Ketobutenolide 3, easily obtained from santonin (1), has been transformed into two natural furanoeudesmanes 4 and 5, isolated from Commiphora molmol and Tubipora musica, respectively. trans- And cis-decalin systems were obtained by stereoselective reduction of the C(4)-C(5) double bond in 3 in the following way: hydrogenation of 3 over Pd/C followed by acidic treatment gave the cis isomer 10 as the major product; selective hydrogenation of the C(1)-C(2) double bond with the Wilkinson's catalyst followed by reduction with NaTeH yielded mainly the trans isomer 9. Compounds 9 and 10 were transformed into 4 and 5 in parallel sequences. Optical rotation and CD measurements of the synthetic products revealed that the stereochemistry of both natural products should be revised to their enantiomeric form.     

Bulk material vs. single crystal: powder diffraction to the rescue

The crystal structure of bulk microcrystalline material obtained by interaction of two rigid building blocks, namely dirhodium(ii) tetra(trifluoroacetate), [Rh2(O2CCF3)4], and bis(4'-pyridyl)diphenylsilane, (C6H5)2Si(C5H4N)2, has been solved ab initio using X-ray powder diffraction data. The title product of the 1 [ratio] 1 composition, [Rh2(O2CCF3)4.(mu2-(C6H5)2Si(C5H4N)2)], is a one-dimensional zigzag polymer built on axial Rh...N interactions averaged at 2.16 A. Its structural characterization complements the previously reported product of the 2:1 composition obtained from the same reaction, namely {[Rh2(O2CCF3)4]2.(mu4-(C6H5)2Si(C5H4N)2)}. The latter has a 2D layered network revealed by the single crystal diffraction study. A combination of powder and single crystal X-ray techniques is shown to be methodologically important and complementary for understanding of product assembling in the system.     

(C_5H_9C_5H_4)_3NdBrLi(THF)_3和(C_5H_9C_5H_4)_3SmTHF的合成与结构

无水三氯化钕与环戊烷基环戊二烯钠、溴化锂(1:2:1摩尔比)反应,除去不溶物和溶剂后,产物在己烷/四氢呋喃溶剂中冷冻得到兰紫色晶体(C5H9C5H4)3NdBrLi(THF)3(配合物1)。其中心金属Nd3+的配位数为10,以η5与3个环戊二烯基相连,并通过单溴原子桥连锂原子,形成双核结构。该晶体属三斜晶系,P`1空间群。晶体学参数为a=12.048(2)、b=13.498(3)、c=13.831(3);α=104.16(3)、β=104.07(3)、γ=95.96(3); V=2083.3(7)3、Z=2、Dc=1.35Mg/m3、Mr=847.01gmol-1、F(000)=874。无水三氯化钐与环戊烷基环戊二烯钠(1:3)反应,产物在-30oC下的己烷溶剂中结晶得桔红色晶体(C5H9C5H4)3SmTHF(配合物2)。该晶体属正交晶系,Fdd2空间群。晶胞参数a=28.175(5) 、b=46.24(2)、c=9.167(4);V=11943(8)3、Z=16、Dc=1.38Mg/m3、 Mr=622.11 g·mol-1、F(000)=5136。10配位的金属Sm3+与3个环戊二烯基以η5相连,并结合一个四氢呋喃溶剂分子。     

Correlated C-C and C-O bond conformations in saccharide hydroxymethyl groups: parametrization and application of redundant 1H-1H, 13C-1H, and 13C-13C NMR J-couplings

Methyl alpha- and beta-pyranosides of d-glucose and d-galactose 1-4 were prepared containing single sites of (13)C-enrichment at C4, C5, and C6 (12 compounds), and (1)H and (13)C[(1)H] NMR spectra were obtained to determine a complete set of J-couplings ((1)J, (2)J, and (3)J) involving the labeled carbon and nearby protons and carbons within the exocyclic hydroxymethyl group (CH(2)OH) of each compound. In parallel theoretical studies, the dependencies of (1)J, (2)J, and (3)J involving (1)H and (13)C on the C5-C6 (omega) and C6-O6 (theta;) torsion angles in aldohexopyranoside model compounds were computed using density functional theory (DFT) and a special basis set designed to reliably recover the Fermi contact contribution to the coupling. Complete hypersurfaces for (1)J(C5,C6), (2)J(C5,H6)(R), (2)J(C5,H6)(S), (2)J(C6,H5), (2)J(C4,C6), (3)J(C4,H6)(R), (3)J(C4,H6)(S), and (3)J(C6,H4), as well as (2)J(H6)(R)(,H6)(S), (3)J(H5,H6)(R), and (3)J(H5,H6)(S), were obtained and used to parametrize new equations correlating these couplings to omega and/or theta;. DFT-computed couplings were also tested for accuracy by measuring J-couplings in (13)C-labeled 4,6-O-ethylidene derivatives of d-glucose and d-galactose in which values of omega and theta; were constrained. Using a new computer program, Chymesa, designed to utilize multiple J-couplings sensitive to exocyclic CH(2)OH conformation, the ensemble of experimental couplings observed in 1-4 were analyzed to yield preferred rotamer populations about omega and theta;. Importantly, due to the sensitivity of some couplings, most notably (2)J(H6)(R)(,H6)(S), (2)J(C5,H6)(R), and (2)J(C5,H6)(S), to both omega and theta;, unique information on correlated conformation about both torsion angles was obtained. The latter treatment represents a means of evaluating correlated conformation in 1,6-linked oligosaccharides, since psi and theta; are redundant in these linkages. In the latter regard, multiple, redundant scalar couplings originating from both sides of the glycosidic linkage can be used collectively to evaluate conformational correlations between psi/theta; and C5-C6 bond rotamers.     

One-pot two-step enzymatic coupling of pyrimidine bases to 2-deoxy-D-ribose-5-phosphate. A new strategy in the synthesis of stable isotope labeled deoxynucleosides

The enzymatic synthesis of thymidine from 2-deoxy-D-ribose-5-phosphate is achieved, in a one-pot two-step reaction using phosphoribomutase (PRM) and commercially available thymidine phosphorylase (TP). In the first step the sugar-5-phosphate is enzymatically rearranged to alpha-2-deoxy-D-ribose-1-phosphate. Highly active PRM is easily obtained from genetically modified overproducing E. coli cells (12,000 units/84 mg protein) and is used without further purification. In the second step thymine is coupled to the sugar-1-phosphate. The thermodynamically unfavorable equilibrium is shifted to the product by addition of MnCl(2) to precipitate inorganic phosphate. In this way the overall yield of the beta-anomeric pure nucleoside increases from 14 to 60%. In contrast to uracil, cytosine is not accepted by TP as a substrate. Therefore, 2'-deoxy-cytidine is obtained by functional group transformations of the enzymatically prepared 2'-deoxy-uridine. The method has been demonstrated by the synthesis of [2',5'-(13)C(2)]- and [1',2',5'-(13)C(3)]thymidine as well as [1',2',5'-(13)C(3)]2'-deoxyuridine and [3',4'-(13)C(2)]2'-deoxycytidine. In addition the nucleoside bases thymine and uracil are tetralabeled at the (1,3-(15)N(2),2,4-(13)C(2))-atomic positions. All compounds are prepared without any scrambling or dilution of the labeled material and are thus obtained with a very high isotope enrichment (96-99%). In combination with the methods that have been developed earlier it is concluded that each of the (13)C- and (15)N-positions and combination of positions of the pyrimidine deoxynucleosides can be efficiently labeled starting from commercially available and highly (13)C- or (15)N-enriched formaldehyde, acetaldehyde, acetic acid, potassium cyanide, methylamine hydrochloride, and ammonia.     

Dynamic stereochemistry of erigeroside by measurement of 1H-1H and 13C-1H coupling constants

Erigeroside was extracted from Satureja khuzistanica Jamzad (Marzeh Khuzistani in Persian, family of lamiaceae), and (1)H, (13)C, (13)C{(1)H}, (1)H-(1)H COSY, HMQC and J-HMBC were obtained to identify this compound and determine a complete set of J-coupling constants ((1)J(C-H), (2)J(C-H), (3)J(C-H) and (3)J(H-H)) values within the exocyclic hydroxymethyl group (CH(2)OH) and anomeric center. In parallel, density functional theory (DFT) using B3LYP functional and split-valance 6-311++G** basis set has been used to optimized the structures and conformers of erigeroside. In all calculations solvent effects were considered using a polarized continuum (overlapping spheres) model (PCM). The dependencies of (1)J, (2)J and (3)J involving (1)H and (13)C on the C(5')-C(6') (omega), C(6')-O(6') (theta) and C(1')-O(1') (phi) torsion angles in erigeroside were computed using DFT method. Complete hyper surfaces for (1)J(C1',H1'), (2)J(C5',H6'R), (2)J(C5',H6'S), (2)J(C6',H5'), (3)J(C4',H6'R), (3)J(C4',H6'S) and (2)J(H6'R-H5'S) as well as (3)J(H5',H6'R) were obtained and used to derive Karplus equations to correlate these couplings to omega, theta and phi. These calculated J-couplings are in agreement with experimental values. These results confirm the reliability of DFT calculated coupling constants in aqueous solution.     

Synthesis and Crystal Structure of 2,3-Diethoxycarbonyl-4-phenyl-5-morpholinyl Thiophene

1INTRoDUCTIONa-Thiocarbonylthioformamidesweresynthesizedin198o[l~2i,however,thereisnoreportofthesecompoundsconcerningtheirpropertiesandreactionactivitiest33.Accordingtotheirstructure,theyseemtohavereactionwithdienophi1es,likesubsti-tutedolefinicandacetylenicdienophilestoleadcorrespondingDiels-Alderproduct.xylene(15ml),diethylbutynedioicester(O.2g,1.2mmol)wasadded,themix-turewasrefluxedfor20h,thencooledtoroomtemperatureandconcentrated.Theresiduewaspurifiedbysilicagelcolumnusingacetone/petr…     

Selective extraction of higher fullerenes using cyclic dimers of zinc porphyrins

Higher fullerenes (>/=C76) were selectively extracted from a fullerene mixture obtained from a combustion-based industrial production source by cyclic dimers of beta-unsubstituted porphyrin zinc complexes 2C5-2C7 with C5-C7 alkylene spacers as host molecules. Results of single extraction of the fullerene mixture with 2C5-2C7 together with a beta-substituted analogue of 2C6 (1C6) and spectroscopic titration of 2C6 and 1C6 with C60, C70, and C96 indicated that the host selectivity toward higher fullerenes is much dependent on the structure of the porphyrin units and the size of the host cavity. Sequential three-stage extraction of the fullerene mixture with the best-behaved 2C6 resulted in considerable enrichment in very rare fullerenes C102-C110 (<0.1 abs %) up to 82 abs % (C76-C114, 99 abs %) (356 nm) of total fullerenes.     

Synthesis and thermal characterization of novel poly(tetramethyl‐1,3‐silphenylenesiloxane) derivative with phenol moiety in the main chain

Novel poly(tetramethyl‐1,3‐silphenylenesiloxane) derivative with phenol moiety in the main chain, that is, poly(tetramethyl‐5‐hydroxy‐1,3‐silphenylenesiloxane) ( P1 ), was synthesized and the thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetry (TG). P1 was obtained via deprotective hydrogenation of poly(tetramethyl‐5‐benzyloxy‐1,3‐silphenylenesiloxane) ( Pre‐P1 ) catalyzed by 10% palladium on charcoal as well as via direct polycondensation of 3,5‐bis(dimethylhydroxysilyl)phenol ( M2 ). Pre‐P1 was obtained by polycondensation of 1,3‐bis(dimethylhydroxysilyl)‐5‐benzyloxybenzene ( M1 ), catalyzed by 1,1,3,3‐tetramethylguanidinium 2‐ethylhexoate. M1 was prepared by the Grignard reaction using chlorodimethylsilane and 1,3‐dibromo‐5‐benzyloxybenzene followed by the hydrolysis catalyzed by 5% palladium on charcoal. M2 was prepared by deprotective hydrogenation of M1 catalyzed by 10% palladium on charcoal. The obtained P1 was soluble in common organic solvents such as tetrahydrofuran, chloroform, dichloromethane, toluene, and so forth as well as in highly polar solvents as ethanol and methanol in which poly(tetramethyl‐1,3‐silphenylenesiloxane) is insoluble. The glass transition temperature (T_g) of P1 was determined to be 40 °C from DSC, which was much higher than that of poly(tetramethyl‐1,3‐silphenylenesiloxane) (?52 °C), indicating that the intermolecular and/or intramolecular hydrogen bondings based on hydroxyl groups restricted the mobility of the main chain. The temperature at 5% weight loss (T_d5) of P1 (393 °C) determined by TG was lower than that of poly(tetramethyl‐1,3‐silphenylenesiloxane) (ca. 500 °C), indicating that the phenol moieties decline the thermal stability; however, the obtained P1 would promise to be a new reactive‐polymer with phenolic–hydroxyl moieties to develop new functional materials. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 692–701, 2008     

Syntheses of the C(1-6) and C(19-24) fragments of lituarines A, B, and C

[structure: see text] Lituarines A-C are marine natural products comprising a tricyclic spiroacetal bridged at C(8) and C(18) by a functionalized ester linkage conceptually obtained from a C(19-24) alcohol and a C(1-6) carboxylic acid whose oxidation level varies at C(4) and C(5). Stereoselective routes are described to compounds 26 and 27, fully functionalized ester fragments of lituarine A and lituarines B and C, respectively.