bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid‐Delivery MOCVD of Strontium Bismuth Tantalate Thin Films Using Sr[Ta(OC2H5)5(OCH2CH2OCH3)]2 and Liquid Bi(CH2CH=CH2)3 as Precursors
Authors: Hyeon J.‐Y. , Lisker M. , Silinskas M. , Burte E. , Edelmann F. T. 
Published: April 2005

AbstractThin films of BiOX, SrXTaYOZ, and strontium bismuth tantalate (SBT) were deposited by metal‐organic (MO)CVD on 150 mm silicon (100) wafers. Some of the wafers were pre‐deposited with Pt electrodes. The substrate temperature and the deposition pressure were varied from 300 °C to 600 °C and from 0.35 mbar to 7 mbar, respectively. Bi(CH2CH=CH2)3 (triallylbismuth) and Sr[Ta(OEt)5(OC2H4OMe)]2 (strontium‐bis[tantalum(pentaethoxide)(2‐methoxyethoxide)]) were used as Bi precursor and as Sr‐Ta precursor, respectively. A liquid delivery system was used to supply and to vaporize the precursors into the reactor. X‐ray photoelectron spectroscopy (XPS) and ellipsometry were carried out to characterize the film properties. The growth rate of the MOCVD of BiOX and SrXTaYOZ was compared to the growth rate of SBT to obtain information about mutual interaction between the precursors. The deposition rate of bismuth oxide thin films was low (∼10 nm h–1 at 0.35 mbar) and virtually independent of the temperature. On the contrary, the growth rate of strontium tantalate films depended strongly on the temperature. The deposition rate of the SBT films was similar to the bismuth oxide film deposition, which slightly increased with increasing substrate temperature. However, the deposition rate of SBT was always lower than deposition rate of the single precursors. The growth rate significantly depended on pressure. The decrease of the deposition pressure in the reactor chamber reduced the deposition rate of BiOX, SrXTaYOZ, and SBT but on the other hand, it improved the uniformity of the film thickness. XPS measurements showed a deficit of bismuth in the SBT films even though the concentration of the Bi precursor had been several times higher than the concentration of Sr‐Ta precursor. The XPS depth‐profiling by Ar+ ion sputtering indicated more metallic bond characteristics of Ti, Sr, and Bi after ion‐beam bombardment.
Deposition of Silver Thin Films Using the Pyrazolate Complex [Ag(3,5‐(CF3)2C3HN2)]3
Authors: Chi Y. , Lay E. , Chou T.‐Y. , Song Y.‐H. , Carty A. J. 
Published: April 2005

AbstractThe synthesis and characterization of a series of silver pyrazolate complexes [Ag(tfpz)]3 (1), [Ag(fbpz)]3 (2), [Ag(dbpz)]3 (3), and [(py)Ag(tfpz)]2 (4) are reported, for which tfpz, fbpz, dbpz are abbreviations for the pyrazolate ligands with formulae 3,5‐(CF3)2‐pz, 3‐tBu‐5‐(CF3)‐pz, and 3,5‐(tBu)2‐pz, respectively. These silver complexes were characterized by microanalysis and spectroscopic methods. The CF3‐substituted complex 1 possesses the highest volatility and stability against thermal decomposition. Low pressure CVD experiments were conducted over the temperature range 250–350 °C. Silver metal thin films were successfully obtained on silicon wafers using pure H2 as the carrier gas. Scanning electron microscopy (SEM) was used to reveal surface morphologies, while X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD) were utilized to determine the atomic composition of the as‐deposited thin films as well as the crystallite packing.
Synthesis, Molecular Structure and Reactivity of a Calix[4]arene Monomethyl Ether Supported Nitridomolybdenum Complex
Authors: Zeller Jürgen , Büschel Susanne , Reiser Benjamin K. H. , Begum Farida , Radius Udo 
Published: April 2005

AbstractThe calix[4]arene monomethyl ether supported nitridomolybdenum complex [MoN(MeCalix)] (1) was obtained in high yield from the reaction of [MoN(OtBu)3] and calix[4]arene methyl ether (H3MeCalix). Contrary to the calix[4]arene dimethyl ether supported dioxomolybdenum complex [MoO2(paco‐Me2Calix)] published earlier, the calix[4]arene ligand in 1 adopts a cone conformation. Complex 1 reacts smoothly with GaCl3 and GaEt3 to yield the compounds [Mo(NGaCl3)(MeCalix)] (2) and [Mo(NGaEt3)(MeCalix)] (3), respectively. Complex 2 is the first structurally characterized example of a nitrido‐bridged dinuclear compound of a group 6 metal and a group 13 halide (EX3). The [Mo≡N–GaCl3] unit, in which both metal atoms are unsymmetrically bridged with a short Mo≡N and a long Ga–N contact, shows significant bending at the nitrido bridge. This deviation from a linear alignment is attributed to packing forces. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Group II Intron Ribozymes and Metal Ions – A Delicate Relationship
Authors: Sigel Roland K. O. 
Published: April 2005

AbstractGroup II introns are naturally occurring ribozymes in plants, fungi, bacteria, and lower eukaryotes that undergo a fascinating array of reactions. These large molecular machines with a size ranging between 600 and 2500 nucleotides are self‐splicing introns also capable of reinserting themselves into RNA or DNA, thus making them mobile genetic elements. The structural information available on group II intron ribozymes is very scarce. So far, only one crystal structure and one NMR solution structure of two domains located in the catalytic core are available. For proper folding and function, each intron requires specific concentrations of monovalent and divalent metal ions. Although most of these metal ions are used for charge screening, some are bound to distinct sites as has been shown by hydrolytic cleavage experiments. These specifically bound ions are crucial for tertiary contact formation and catalysis. This review will discuss the different metal‐ion requirements of self‐splicing group II introns, the available structural data and information on the binding location and affinity of metal ions, as well as the methods applied to investigate the metal‐ion binding properties of these large RNAs. Due to the size of these introns, the richness of local structures, the catalytic versatility and the involvement of metal ions in all of the above‐mentioned aspects, group II introns are an ideal target to be studied by combined means from the fields of Biochemistry, Molecular Biology, Analytical, and (Bio)Inorganic Chemistry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Molecular Recognition: Use of Metal‐Containing Molecular Clefts for Supramolecular Self‐Assembly and Host–Guest Formation
Authors: Crowley James D. , Bosnich Brice 
Published: April 2005

AbstractMolecular clefts consisting of a rigid spacer linked to two parallel cofacially disposed terpy‐M–X (M = Pd2+, Pt2+) units, which can vary in separation from 6.6 to 7.2 Å, have been used as molecular receptors and for self‐assembly with linear and triangular linkers to produce rectangles and trigonal prisms, respectively. Aromatic molecules form multiple host–guest adducts with the molecular cleft receptors and with the rectangles and trigonal prisms. Planar complexes of Pt2+ also form host–guest adducts. The forces that control this molecular recognition, namely, π‐π interactions, charge‐induced dipole interactions, charge‐charge forces, weak metal‐metal interactions and solvation effects, are discussed and assigned to the various adducts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
The Associative Properties of Some Amphiphilic Fullerene Derivatives
Authors: Angelini Guido , Cusan Claudia , De Maria Paolo , Fontana Antonella , Maggini Michele , Pierini Marco , Prato Maurizio , Schergna Stefano , Villani Claudio 
Published: April 2005

AbstractThe hydrophilic vs. hydrophobic balance for five C60 derivatives (FD1–5) bearing one hydrophilic addend has been evaluated by means of useful descriptors derived from (i) aggregation measurements in aqueous/organic mixtures, (ii) partition measurements between n‐octanol and water (log Pm/a), and (iii) retention factors in reverse‐phase chromatography (log kw). Aggregates of FD1–5 have been obtained both in water and in aqueous organic mixtures. The dimension of the aggregates has been estimated by gel‐permeation chromatography. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Nucleophilic Reactivities of Silyl Ketene Acetals and Silyl Enol Ethers Containing (C6F5)3SiO and (C6H5)3SiO Groups
Authors: Dilman Alexander D. , Mayr Herbert 
Published: April 2005

AbstractThe kinetics of the reactions of tris(pentafluorophenyl)silyl and triphenylsilyl ketene acetals and enol ethers with benzhydrylium cations have been measured photometrically. The second‐order rate constants (log k2) have been used to determine the nucleophilicity parameters of these π systems, which provide a quantitative comparison of their reactivities with those of other types of nucleophiles. A change from trimethylsilyloxy to triphenylsilyloxy reduces reactivity by only a factor of ten, while replacement of triphenylsilyloxy with tris(pentafluorophenyl)silyloxy decreases the nucleophilicity of the enolate C=C double bond by three to four orders of magnitude. The cation‐stabilizing ability of the tris(pentafluorophenyl)silyloxy group is thus similar to that of a methyl group. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Asymmetric Cyanohydrin Synthesis Catalyzed by Al(salen)/Triphenylphosphane Oxide
Authors: Kim Sung Soo , Song Dae Ho 
Published: April 2005

AbstractVarious aldehydes undergo asymmetric trimethylsilylcyanation with (CH3)3SiCN (TMSCN) in the presence of a chiral Al(salen) complex and Ph3PO as the catalyst. This is a double activation where Al(salen) plays the role of Lewis acd and POPh3 acts as a Lewis base. Various kind of aldehydes were subjected to the enantioselective addition of (CH3)3SiCN at temperatures between –40 °C and –50 °C. Hydrolysis of the adducts gave cyanohydrins with over 90 % yield and 80 % ee in most cases. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Pyrimidine‐Annulated Pyrrolobenzodiazepines. A New Ring System Related to Aspergillus Alkaloids
Authors: Schmidt Andreas , Gholipour Shilabin Abbas , Christoph Namyslo Jan , Nieger Martin , Hemmen Sascha 
Published: April 2005

AbstractPyrrolo[2,1‐c][1,4]benzodiazepine‐5,11‐dione was converted into the corresponding C‐11‐monothiolactam and subsequently treated with amines to give cyclic amidines, which racemize due to the formation of tautomers (NMR, X‐ray analysis) under basic conditions. We treated these amidines with bis(trichlorophenyl) malonate esters. Formation of neutral tautomers of the 1,3,8‐triones of the new 4,7a,12b‐triaza‐dibenzo[e,g]azulene ring system gave a twisted molecule with both helical and chiral structure elements (NMR, X‐ray analysis), which caused a splitting of the NMR signals into two sets. Results of two X‐ray single crystal analyses are presented, together with an ab initio calculation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Studies Towards the Synthesis of Functionalized Medium‐Sized Carbocyclic and Fused Bicyclic Systems by Alkoxy Radical Fragmentation (ARF)
Authors: Ramesh Namakkal G. , Hassner Alfred 
Published: April 2005

AbstractThe stereoselective construction of polyfunctionalized medium‐sized carbocyclic and fused bicyclic systems from substituted bicyclo[3.n.1]alkanones has been studied; the strategy employed involved Suarez’s alkoxy radical fragmentation reaction (ARF) as the key step. The scope of the reaction was examined and this methodology was found to be especially useful for stereo‐ and regioselective construction of eight‐membered carbocycles including bicyclo[6.4.0]dodecane systems, a framework that is present in a variety of biologically active natural products. This reaction was also used successfully in the synthesis of seven‐membered carbocycles but with low selectivity. It was found that the presence of a hemiketal functionality in the molecule is essential for the ARF reaction to occur; hence nine‐ and ten‐membered ring analogs could not be attained since the precursor bicyclic ketones do not form the required hemiketals. This is borne out by MM calculations. Finally, a diquinane was also synthesized. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Phosphonate Modification for a Highly (Z)‐Selective Synthesis of Unsaturated Esters by Horner–Wadsworth–Emmons Olefination
Authors: Touchard François P. 
Published: April 2005

AbstractThe Horner–Wadsworth–Emmons (HWE) reaction of various ethyl diarylphosphonoacetates with benzaldehyde, cyclohexane carboxaldehyde and octanal is reported. Selectivities of up to 98 % at –78 °C are obtained with the three substrates. Among all the phosphonates prepared, the reagent based on 2‐tert‐butylphenol proved to be especially efficient, with Z/E ratios close to 95:5 at 0 °C. It appears thus to be the reagent of choice for the (Z)‐selective HWE reaction with both aromatic and aliphatic aldehydes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Preparation of 3‐(Fluoroalkyl)‐2‐azadienes and Its Application in the Synthesis of (Fluoroalkyl)isoquinoline and ‐pyridine Derivatives
Authors: Palacios Francisco , Alonso Concepción , Rodríguez Marta , Martínez de Marigorta Eduardo , Rubiales Gloria 
Published: April 2005

AbstractA method for the preparation of 3‐(fluoroalkyl)‐substituted 2‐azabutadienes 5 by aza‐Wittig reaction of N‐vinylic 3‐(fluoroalkyl)phosphazenes 4 and aldehydes is reported. Thermal 6π‐electrocyclization of these azadienes gives 3‐(fluoroalkyl)‐substituted isoquinolines 6. Also [4+2] cycloaddition of these heterodienes 5 with enamine 8 gives fluoroalkyl‐substituted pyridine derivatives 10–16. However, the reaction of azadienes 17 with azo compound 18 affords bicyclic heterocycles 19. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Intramolecular Heck Reactions for the Synthesis of the Novel Antibiotic Mensacarcin: Investigation of Catalytic, Electronic and Conjugative Effects in the Preparation of the Hexahydroanthracene Core
Authors: Tietze Lutz F. , Stewart Scott G. , Polomska Marta E. 
Published: April 2005

AbstractThe intramolecular Heck reaction of the three complex diphenyl substrates rac‐2, 5 and rac‐6, containing substituents with different electronic and conjugative properties, were examined. The Pd compounds [Pd2(dba)3]/[(tBu)3PH]BF4, [Pd2(OAc)2{P(o‐Tol)3}2] (4), [PdCl2(PPh3)2] and Pd(OAc)2 were used as catalysts. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Further Synthetic Studies Towards the Austrodorane Skeleton: Synthesis of Austrodoral
Authors: Kulciţki Veaceslav , Ungur Nicon , Gavagnin Margherita , Carbone Marianna , Cimino Guido 
Published: April 2005

AbstractThe synthesis of austrodoral (1), a marine nor‐sesquiterpene that contains a unique bicyclic skeleton, has been achieved. The synthetic strategy is based on the ring contraction of a suitable optically active drimanic epoxy derivative, obtained from commercially available (+)‐sclareolide (4). Fluorosulfonic acid was found to promote the ring contraction efficiently. The nor‐sesquiterpene hydrocarbon 13, a key intermediate in the synthesis of sesquiterpene hydroquinones, has also been prepared in optically active form. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Facial Diastereoselectivity in Cationic Propargylations with Planar‐Chiral AreneCr(CO)3‐Substituted Propargyl Cations
Authors: Netz Astrid , Polborn Kurt , Nöth Heinrich , Müller Thomas J. J. 
Published: April 2005

AbstractThe planar‐chiral (o‐methoxyphenyl)chromium tricarbonyl‐substituted propargyl cation 4 reacts with silyl enol ether derivatives 5 with poor and with enamines 6 with good facial diastereoselectivity to give rise to the (arene)carbonylchromium‐substituted propargylated cyclohexan‐2‐ones 7 and 8, carboxylic acid 9, γ‐lactone 10, cyclopentan‐2‐one 11, and esters 16 and 17. Structural correlations were unambiguously deduced from X‐ray structure analyses of 7a, 9a, and 17a. The origin of facial diastereoselectivity with this class of organometallic electrophiles lies in steric and stereoelectronic biases rather than in purely electronic nucleophilicity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Silver(I)‐Catalysed Protiodesilylation of 1‐(Trimethylsilyl)‐1‐alkynes
Authors: Carpita Adriano , Mannocci Luca , Rossi Renzo 
Published: April 2005

AbstractA procedure for protiodesilylation of 1‐(trimethylsilyl)‐1‐alkynes that involves the use of catalytic amounts of AgNO3 and does not require the employment of KCN is described. This procedure allows for chemoselective deprotection of 1‐(trimethylsilyl)‐1‐alkynes containing α‐(trimethylsilyl)benzyl moieties, tert‐butyldiphenylsilyl alkyl ethers or tert‐butyldimethylsilyl aryl ether groups. However, it causes complete desilylation of 1‐(trimethylsilyl)‐1‐alkynes characterised by a primary alcoholic group protected as a tert‐butyldimethylsilyl ether. Interestingly, compounds that contain this last functional group can also furnish the corresponding alcohols by treatment with a catalytic amount of aqueous HNO3. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Synthesis and Biological Evaluation of Apicularen A Analogues
Authors: Petri Andreas F. , Sasse Florenz , Maier Martin E. 
Published: April 2005

AbstractReactions between amide anions and propanal derivatives containing benzolactone components at their 3‐positions produced hemiaminals, which were dehydrated via the corresponding acetates to provide the apicularen A analogues 21, 29, 34, 38, and 41. Of these, 21 and 29 contain the intact enamide side chain of apicularen A but have modifications in the macrolactone core. On the other hand, compounds 34, 38, and 41 are characterized by the natural core structure but are modified in the enamide part. Biological studies showed that 21 and 29 are quite active but that the other three analogues show only minor activities. The 11‐deoxy analogue 21 turned out to be the most active compound against a mdr cell line. It can be concluded that the macrolactone part of apicularen A will tolerate modifications to some degree, whereas the enamide part is rather sensitive towards structural modifications. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Stereoselective Chloro‐Deboronation Reactions Induced by Substituted Pyridine–Iodine Chloride Complexes
Authors: Batsanov Andrei S. , Howard Judith A. K. , Lightfoot Andrew P. , Twiddle Steven J. R. , Whiting Andrew 
Published: April 2005

AbstractA novel class of charge‐transfer complexes based on iodine chloride and substituted pyridines, which possess a number of interesting and unique structural features, can be employed to bring about a stereocontrolled chloro‐deboronation of certain vinyl boronates to generate the (1Z)‐alkenyl chlorides in good yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Preparation of Enantiomerically Pure [3]Ferrocenophane‐Based Chelate Bis‐Phosphane Ligands and Their Use in Asymmetric Alternating Carbon Monoxide/Propene Copolymerization
Authors: Liptau Patrick , Tebben Ludger , Kehr Gerald , Fröhlich Roland , Erker Gerhard , Hollmann Frank , Rieger Bernhard 
Published: April 2005

AbstractAn intramolecular Mannich reaction (HNMe2, TiCl4) was used to convert 1,1'‐diacetylferrocene to the unsaturated amino[3]ferrocenophane 2. Subsequent hydrogenation gave 3. To obtain enantiomerically pure chelate P,P‐[3]ferrocenophane ligands the readily available pure dimethylamino[3]ferrocenophane enantiomers (R,R)‐3 and (S,S)‐3 each were treated with butyllithium followed by chlorodiphenylphosphane to yield the chelate P,N‐[3]ferrocenophanes (R,R,Rpl)‐10 and (S,S,Spl)‐10, respectively. Their treatment with HPPh2 in glacial acetic acid resulted in substitution of the –NMe2 group by –PPh2 with overall retention of configuration to yield (R,R,Rpl)‐11 and (S,S,Spl)‐11, respectively (both characterized by X‐ray diffraction). Similarly, the reaction of (R,R,Rpl)‐10 or (S,S,Spl)‐10 with dicyclohexylphosphane/HOAc yielded the pure (R,R,Rpl)‐12 and (S,S,Spl)‐12 enantiomers, respectively. Both these compounds were also characterized by X‐ray crystal structure analyses. (R,R,Rpl)‐12 was employed in catalytic asymmetric hydrogenation and also in asymmetric alternating carbon monoxide/propene copolymerization. A catalyst that was generated in situ from the chelate P,P‐[3]ferrocenophane ligand and palladium acetate gave the CO/propene alternating copolymer with a good activity and high asymmetric induction. The catalyst derived from the reaction of (R,R,Rpl)‐11 with [Rh(cod)2]BF4 was employed in the enantioselective hydrogenation of dimethyl itaconate (DMI) (13, ca. 95 % ee, R‐configured product) and methyl α‐acetamidocinnamate (MAC) 14 (ca. 24 % ee, R‐configured product). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Elemental Fluorine and HOF·CH3CN in Service of General Organic Chemistry
Authors: Rozen Shlomo 
Published: April 2005

AbstractAt present, HOF·CH3CN complex is the best oxygen transfer agent that chemistry has to offer. It is readily made by passing dilute fluorine through aqueous acetonitrile and does not require any isolation or purification. It is stable in aqueous acetonitrile solution for a few hours at room temperature, providing ample opportunities for various reactions. Epoxidation of regular olefins as well as of very electron‐depleted ones proceeds smoothly. HOF·CH3CN transfer oxygen also to heteroatoms, especially sulfur and nitrogen. Even very electron‐depleted sulfides such as RfSAr that are very difficult to oxidize, are converted into the respective sulfones in a matter of minutes. On the other hand, since the reaction conditions are very mild, the reagent can oxidize various thiophenes and amino acids to the corresponding S,S‐dioxides and α‐nitro acid derivatives. HOF·CH3CN was also instrumental in ending the 50 years quest for making the elusive 1,10‐phenanthroline N,N‐dioxide and for the novel transformation of azides to nitro derivatives. The use of BrF3 for making symmetric esters and of tBuOF as an electrophilic tert‐butoxylation agent is also mentioned. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
A Highly Efficient Synthesis of Rocaglaols by a Novel α‐Arylation of Ketones
Authors: Diedrichs Nicole , Ragot Jacques P. , Thede Kai 
Published: April 2005

AbstractRocaglaols are natural products exhibiting a range of biological activities. A new synthetic method for the α‐arylation of ketones allows for the synthesis of previously inaccessible rocaglaol derivatives. The key sequence consists of a previously unreported Suzuki type reaction using brominated silyl enol ethers as substrates followed by deprotection of the arylated silyl enol ethers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Enantioselective Synthesis of Thiosulfinates and of Acyclic Alkylidenemethylene Sulfide Sulfoxides
Authors: Colonna Stefano , Pironti Vincenza , Drabowicz Jozef , Brebion Franck , Fensterbank Louis , Malacria Max 
Published: April 2005

AbstractEnantioselectivities up to 75 % have been found in the catalytic mono‐oxidation of di‐tert‐butyl disulfide and related compounds as well as of ketene‐S,S‐acetals with an in situ generated chiral dioxirane. The effect of solvents on the enantiomeric excess has also been examined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)