Chemoselective transfer hydrogenation to nitroarenes mediated by cubane-type Mo3S4 cluster catalysts

Chemoselective cubes: Cubane-type [Mo(3)S(4)X(3)(dmpe)(3)](+) clusters (dmpe = 1,2-(bis)dimethylphosphinoethane), in combination with an azeotropic 5:2 mixture of HCOOH and NEt(3) as the reducing agent, act as selective cluster catalysts (X = H) or precatalysts (X = Cl) for the transfer hydrogenation of functionalized nitroarenes, without the formation of hazardous hydroxylamines.     

Consecutive intermolecular reductive hydroamination: cooperative transition-metal and chiral Brønsted acid catalysis

Enantiomerically pure chiral amines are of increasing importance and commercial value in the fine chemical, pharmaceutical, and agrochemical industries. Here, we describe the straightforward synthesis of chiral amines by combining the atom-economic and environmentally friendly hydroamination of alkynes with an enantioselective hydrogenation of in situ generated imines by using inexpensive hydrogen. By following this novel approach, a wide range of terminal alkynes can be reductively hydroaminated with primary amines including alkyl-, and arylalkynes as well as aryl and heteroaryl amines. Excellent yields and selectivities up to 94?%?ee and 96?% isolated yield were obtained.     

Qualitative screening for volatile organic compounds in human blood using solid‐phase microextraction and gas chromatography‐mass spectrometry

A fast and simple screening procedure using solid‐phase microextraction and gas chromatography‐mass spectrometry (SPME‐GC‐MS) in full‐scan mode for the determination of volatile organic compounds (VOC) is presented. The development of a fast and simple screening technique for the simultaneous determination of various volatiles is of great importance, because of their widespread use, frequent occurrence in forensic toxicological questions and the fact that there is often no hint on involved substances at the crime scene. To simulate a screening procedure, eight VOC with different chemical characteristics were chosen (isoflurane, halothane, hexane, chloroform, benzene, isooctane, toluene and xylene). To achieve maximum sensitivity, variables that influence the SPME process, such as type of fiber, extraction and desorption temperature and time, agitation and additives were optimized by preliminary studies and by means of a central composite design. The limits of detection and recoveries ranged from 2.9 µg/l (xylene) to 37.1 µg/l (isoflurane) and 7.9% (chloroform) to 61.5% (benzene), respectively. This procedure can be used to answer various forensic and toxicological questions. The short time taken for the whole analytical procedure may make its eventual adoption for routine analysis attractive. Copyright © 2010 John Wiley & Sons, Ltd.     

Phosphane Copper(I) Dicarboxylates: Synthesis and Their Potential Use as Precursors for the Spin‐coating Process in the Deposition of Copper

Dicopper dicarboxylates [(R₃P)_mCuXCu(PR₃)_m] ( 5a , X = O₂CCO₂, R = Ph, m = 2; 5b , X = O₂CCO₂, R = nBu, m = 3) were prepared by treatment of [Cu₂O] ( 1a ) with HO₂CCO₂H ( 2a ) in presence of PR₃ ( 4a , R = Ph; 4b , R = nBu). A further synthesis approach to mono‐ and dicopper dicarboxylates is given using an electrolysis cell equipped with Cu electrodes and charged with acids H₂X and phosphanes R₃P. Without addition of a base mononuclear [(nBu₃P)_mCuXH] ( 6a , m = 3, XH = O₂CCO₂H, 6b , m = 3, XH = O₂CCH₂CO₂H, 6c , m = 3, XH = O₂CCH₂CH₂CO₂H, 6d , m = 2, XH = O₂C‐2‐C₅H₄N‐6‐CO₂H) was formed, whereas in presence of NEt₃ ( 3 ), the dicopper systems [(R₃P)_mCuXCu(PR₃)_m] ( 5a , X = O₂CCO₂, R = Ph, m = 2; 5b , X = O₂CCO₂, R = nBu, m = 3; 5c , X = O₂CCH₂CO₂, R = nBu, m = 3; 5d , X = O₂CCH₂CH₂CO₂, R = nBu, m = 3; 5e , X = O₂C‐2‐C₅H₄N‐6‐CO₂, R = nBu, m = 3) were produced. When 6a reacted with [(tmeda)Zn(nBu)₂] ( 7 ), trimetallic [(tmeda)Zn((nBu₃P)₃CuO₂CCO₂)₂] ( 8 ) was accessible. In this heterobimetallic complex the Zn(tmeda) unit spans two CuO₂CCO₂ entities. The molecular structures of 5a , 6a and 6d in the solid state were determined by single X‐ray structure analysis. Complexes 5a and 6a are monomers, whereas 6d creates in the solid state a linear open chain coordination polymer by hydrogen bridge formation. Characteristic for 6d is the somewhat distorted trigonal bipyrimidal arrangement around the copper atom with the nBu₃P ligands in axial and the C₅H₃NCO₂H oxygen and nitrogen atoms in equatorial positions. In 5a the oxalate connectivity binds in a μ‐1,2,3,4 fashion being part of a planar Cu₂(oxalate) core. TG studies of several mono‐ and dicopper dicarboxylates were carried out. Release of the PR₃ ligands is recognized and the remaining Cu‐(di)carboxylate unit decomposes to afford elemental copper and CO₂. The deposition of copper onto pieces of PVD‐Cu oxidized silicon wafers by applying the spin‐coating process and using 5c and 5d as precursors is discussed.     

Colourimetric Carboxylate Anion Sensors Derived from Viologen‐Based Receptors

A series of tri‐ and tetrapodal viologen‐based anion receptors showing a colourimetric response to carboxylates, such as acetate, have been synthesised. Alteration of the anion binding sites allows for binding site competition within a receptor. This results in a delayed colourimetric response for urea derivatives compared with pyridinium systems because the anions are initially bound to the periphery of the receptor, away from the viologen unit. DFT calculations and experimental measurements allow the colour change to be assigned to an anion–receptor charge‐transfer process, facilitated by the exceptionally low reduction potential of the cationic host compounds. Evidence for electron transfer to give the viologen radical cation is also seen in some cases.     

Eichler–Shimura theory for mock modular forms

We use mock modular forms to compute generating functions for the critical values of modular $L$ -functions, and we answer a generalized form of a question of Kohnen and Zagier by deriving the “extra relation” that is satisfied by even periods of weakly holomorphic cusp forms. To obtain these results we derive an Eichler–Shimura theory for weakly holomorphic modular forms and mock modular forms. This includes two “Eichler–Shimura isomorphisms”, a “multiplicity two” Hecke theory, a correspondence between mock modular periods and classical periods, and a “Haberland-type” formula which expresses Petersson’s inner product and a related antisymmetric inner product on $M_{k}^{!}$ in terms of periods.     

Effects of structural modification on gene transfection and self-assembling properties of amphiphilic dendrimers

A library of novel amphiphilic, self-assembling dendrimers was designed and synthesised to evaluate the effects of structural changes on transfection efficiency.