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Acceptor Character (acceptor + character)
Selected AbstractsBalancing Intermolecular and Molecule,Substrate Interactions in Supramolecular AssembliesADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Dimas G. de Oteyza Abstract Self-assembly of functional supra-molecular nanostructures is among the most promising strategies for further development of organic electronics. However, a poor control of the interactions driving the assembling phenomena still hampers the tailored growth of designed structures. Here exploration of how non-covalent molecule-substrate interactions can be modified on a molecular level is described. For that, mixtures of DIP and F16CuPc, two molecules with donor and acceptor character, respectively are investigated. A detailed study of their structural and electronic properties is performed. In reference to the associated single-component layers, the growth of binary layers results in films with strongly enhanced intermolecular interactions and consequently reduced molecule-substrate interactions. This new insight into the interplay among the aforementioned interactions provides a novel strategy to balance the critical interactions in the assembly processes by the appropriate choice of molecular species in binary supra-molecular assemblies, and thereby control the self-assembly of functional organic nanostructures. [source] Donor-Stabilized Phosphenium Adducts as New Efficient and Immobilizing Ligands in Palladium-Catalyzed Alkynylation and Platinum-Catalyzed Hydrogenation in Ionic LiquidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Samer Saleh Abstract The straightforward synthesis of a new donor-stabilized phosphenium ligand 3d by addition of bromodifurylphosphine to 1,3-dimethylimidazolium-2-carboxylate 1 is described. The obtained ligand exhibits a very strong ,-acceptor character, comparable to that of triphenyl phosphite [P(OPh)3] or of tris-halogenophosphines, with a ,CO(A1) at 2087,cm,1 for its nickel tricarbonyl complex. This ligand, as well as the related 3a which was obtained from chlorodiphenylphosphine, were tested in palladium-catalyzed aryl alkynylation and in the platinum-catalyzed selective hydrogenation of chloronitrobenzenes, both in an ionic liquid phase. In CC bond cross-coupling we observed that the increase of the ,-acceptor character in ligand 3d, due to the introduction of an additional electron-withdrawing group, provides a very efficient catalyst in the alkynylation reaction of aryl bromides with phenylacetylene, including the deactivated 4-bromoanisole or the sterically hindered 2-bromonaphthalene. The catalytic activity decreases with recycling due to the sensitiveness of ligands to protonation in the ionic phase. Conversely, a multiple recycling of the metal/ligand system in non-acidic media was achieved from platinum-catalyzed hydrogenation of m- chloronitrobenzene. The catalytic results obtained by employing the complex of platinum(II) chloride with 3a [trans -PtCl2(3a)2] in comparison with the non-ionic related trans -tris(triphenylphosphine)platinum dichloride [trans -PtCl2(PPh3)2] complex clearly indicate that the simultaneous existence of a strong ,-acceptor character and a positive charge within the ligand 3a significantly increases the life-time of the platinum catalyst. The selectivity of the reaction is also improved by decreasing the undesirable formation of dehalogenation products. This cationic platinum complex trans -PtCl2(3a)2 is the first example of a highly selective catalyst for hydrogenation of chloronitroarenes immobilized in an ionic liquid phase. The system was recycled six times without noticeable metal leaching in the organic phase, and no loss of activity. [source] Synthesis and molecular structure of Cr(salen)(,-N)RhCl(COD): the first example of a heterobimetallic nitride-bridged complex containing chromiumACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2010Johan Vibenholt Five-coordinate Cr(N)(salen) {salen is 2,2,-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolate} reacts with [RhCl(COD)]2 (COD is 1,5-cyclooctadiene) to yield the heterobimetallic nitride-bridged title compound, namely chlorido-2,Cl -[2(,4)-1,5-cyclooctadiene]{2,2,-[ethane-1,2-diylbis(nitrilomethylidyne)]diphenolato-1,4O,N,N,,O,}-,-nitrido-1:2,2N:N -chromium(V)rhodium(I), [CrRh(C16H14N2O2)ClN(C8H12)]. The Cr,N bond of 1.5936,(14),Å is elongated by only 0.035,Å compared to the terminal Cr,N bond in the precursor. The nitride bridge is close to being linear [173.03,(9)°] and the Rh,N bond of 1.9594,(14),Å is very short for a monodentate nitrogen-donor ligand, indicating significant ,-acceptor character of the Cr[triple-bond]N group. [source] Tuning the Magnetic Moment of [Ru2(DPhF)3(O2CMe)L]+ Complexes (DPhF=N,N, -Diphenylformamidinate): A Theoretical Explanation of the Axial Ligand InfluenceCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2010Carmen Barral Dr. Abstract The magnetic behaviour of the compounds containing the [Ru2(DPhF)3(O2CMe)]+ ion (DPhF,=N,N, -diphenylformamidinate) shows a strong dependence on the nature of the ligand bonded to the axial position. The new complexes [Ru2(DPhF)3(O2CMe)(OPMe3)][BF4],0.5,CH2Cl2 (1, 0.5,CH2Cl2) and [Ru2(DPhF)3(O2CMe)(4-pic)][BF4] (2) (4-pic=4-methylpyridine) clearly display this influence. Complex 1,0.5,CH2Cl2 shows a magnetic moment corresponding to a S=3/2 system affected by the common zero-field splitting (ZFS) and a weak antiferromagnetic interaction, whereas complex 2 displays an intermediate behaviour between S=3/2 and S=1/2 systems. The experimental data of complex 1 are fitted with a model that considers the ZFS effect using the Hamiltonian ,D=S,D,S. The weak antiferromagnetic coupling is introduced as a perturbation, using the molecular field approximation. DFT calculations demonstrate that, in the [Ru2(O2CMe)(DPhF)3(L)]+ complexes, the energy level of the metal,metal molecular orbitals is strongly dependent on the nature of the axial ligand (L). This study reveals that the increase in the ,-acceptor character of L leads to a greater split between the ,* and ,* HOMO orbitals. The influence of the axial ligand in the relative energy between the doublet and quartet states in this type of complexes was also analysed. This study was performed on the new complexes 1,0.5,CH2Cl2 and 2. The previously isolated [Ru2(DPhF)3(O2CMe)(OH2)][BF4],0.5,CH2Cl2 (3, 0.5,CH2Cl2) and [Ru2(DPhF)3(O2CMe)(CO)][BF4],CH2Cl2 (4,CH2Cl2) complexes were also included in this study as representative examples of spin-admixed and low-spin configurations, respectively. The [Ru2(DPhF)3(O2CMe)]+ (5) unit was used as a reference compound. These theoretical studies are in accordance with the different magnetic behaviour experimentally observed. [source] Hydrogen-Bonding Cooperativity: Using an Intramolecular Hydrogen Bond To Design a Carbohydrate Derivative with a Cooperative Hydrogen-Bond Donor CentreCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2004Virginie Vicente Dr. Abstract Neighbouring groups can be strategically located to polarise HO,,,OH intramolecular hydrogen bonds in an intended direction. A group with a unique hydrogen-bond donor or acceptor character, located at hydrogen-bonding distance to a particular OH group, has been used to initiate the hydrogen-bond network and to polarise a HO,,,OH hydrogen bond in a predicted direction. This enhanced the donor character of a particular OH group and made it a cooperative hydrogen-bond centre. We have proved that a five-membered-ring intramolecular hydrogen bond established between an amide NH group and a hydroxy group (1,2-e,a), which is additionally located in a 1,3 -cis- diaxial relationship to a second hydroxy group, can be used to select a unique direction on the six-membered-ring intramolecular hydrogen bond between the two axial OH groups, so that one of them behaves as an efficient cooperative donor. Talose derivative 3 was designed and synthesised to prove this hydrogen-bonding network by NMR spectroscopy, and the mannopyranoside derivatives 1 and 2 were used as models to demonstrate the presence in solution of the 1,2-(e,a)/five-membered-ring intramolecular hydrogen bond. Once a well-defined hydrogen-bond is formed between the OH and the amido groups of a pyranose ring, these hydrogen-bonding groups no longer act as independent hydrogen-bonding centres, but as hydrogen-bonding arrays. This introduces a new perspective on the properties of carbohydrate OH groups and it is important for the de novo design of molecular recognition processes, at least in nonpolar media. Carbohydrates 1,3 have shown to be efficient phosphate binders in nonpolar solvents owing to the presence of cooperative hydroxy centres in the molecule. [source] | ||||||||||