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Hydride Complex (hydride + complex)

Distribution by Scientific Domains

Chemistry	90%

Selected Abstracts

Asymmetric Transfer Hydrogenation of Aromatic Ketones Catalyzed by the Iridium Hydride Complex under Ambient Conditions.

CHEMINFORM, Issue 8 2005
Jian-shan Chen
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

The Role of Solvent on the Mechanism of Proton Transfer to Hydride Complexes: The Case of the [W3PdS4H3(dmpe)3(CO)]+ Cubane Cluster

CHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2010
Andrés
Abstract The kinetics of reaction of the [W3PdS4H3(dmpe)3(CO)]+ hydride cluster (1+) with HCl has been measured in dichloromethane, and a second-order dependence with respect to the acid is found for the initial step. In the presence of added BF4, the second-order dependence is maintained, but there is a deceleration that becomes more evident as the acid concentration increases. DFT calculations indicate that these results can be rationalized on the basis of the mechanism previously proposed for the same reaction of the closely related [W3S4H3(dmpe)3]+ cluster, which involves parallel first- and second-order pathways in which the coordinated hydride interacts with one and two acid molecules, and ion pairing to BF4, hinders formation of dihydrogen bonded adducts able to evolve to the products of proton transfer. Additional DFT calculations are reported to understand the behavior of the cluster in neat acetonitrile and acetonitrile,water mixtures. The interaction of the HCl molecule with CH3CN is stronger than the WH,,,HCl dihydrogen bond and so the reaction pathways operating in dichloromethane become inefficient, in agreement with the lack of reaction between 1+ and HCl in neat acetonitrile. However, the attacking species in acetonitrile,water mixtures is the solvated proton, and DFT calculations indicate that the reaction can then go through pathways involving solvent attack to the W centers, while still maintaining the coordinated hydride, which is made possible by the capability of the cluster to undergo structural changes in its core. [source]

,-Diketiminate-Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis, Characterization, Adduct Formation, and Reactivity Studies

CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2010
Simon
Abstract The preparation and characterization of a series of magnesium(II) iodide complexes incorporating ,-diketiminate ligands of varying steric bulk and denticity, namely, [(ArNCMe)2CH], (Ar=phenyl, (PhNacnac), mesityl (MesNacnac), or 2,6-diisopropylphenyl (Dipp, DippNacnac)), [(DippNCtBu)2CH], (tBuNacnac), and [(DippNCMe)(Me2NCH2CH2NCMe)CH], (DmedaNacnac) are reported. The complexes [(PhNacnac)MgI(OEt2)], [(MesNacnac)MgI(OEt2)], [(DmedaNacnac)MgI(OEt2)], [(MesNacnac)MgI(thf)], [(DippNacnac)MgI(thf)], [(tBuNacnac)MgI], and [(tBuNacnac)MgI(DMAP)] (DMAP=4-dimethylaminopyridine) were shown to be monomeric by X-ray crystallography. In addition, the related ,-diketiminato beryllium and calcium iodide complexes, [(MesNacnac)BeI] and [{(DippNacnac)CaI(OEt2)}2] were prepared and crystallographically characterized. The reductions of all metal(II) iodide complexes by using various reagents were attempted. In two cases these reactions led to the magnesium(I) dimers, [(MesNacnac)MgMg(MesNacnac)] and [(tBuNacnac)MgMg(tBuNacnac)]. The reduction of a 1:1 mixture of [(DippNacnac)MgI(OEt2)] and [(MesNacnac)MgI(OEt2)] with potassium gave a low yield of the crystallographically characterized complex [(DippNacnac)Mg(,-H)(,-I)Mg(MesNacnac)]. All attempts to form beryllium(I) or calcium(I) dimers by reductions of [(MesNacnac)BeI], [{(DippNacnac)CaI(OEt2)}2], or [{(tBuNacnac)CaI(thf)}2] have so far been unsuccessful. The further reactivity of the magnesium(I) complexes [(MesNacnac)MgMg(MesNacnac)] and [(tBuNacnac)MgMg(tBuNacnac)] towards a variety of Lewis bases and unsaturated organic substrates was explored. These studies led to the complexes [(MesNacnac)Mg(L)Mg(L)(MesNacnac)] (L=THF or DMAP), [(MesNacnac)Mg(,-AdN6Ad)Mg(MesNacnac)] (Ad=1-adamantyl), [(tBuNacnac)Mg(,-AdN6Ad)Mg(tBuNacnac)], and [(MesNacnac)Mg(,- tBu2N2C2O2)Mg(MesNacnac)] and revealed that, in general, the reactivity of the magnesium(I) dimers is inversely proportional to their steric bulk. The preparation and characterization of [(tBuNacnac)Mg(,-H)2Mg(tBuNacnac)] has shown the compound to have different structural and physical properties to [(tBuNacnac)MgMg(tBuNacnac)]. Treatment of the former with DMAP has given [(tBuNacnac)Mg(H)(DMAP)], the X-ray crystal structure of which disclosed it to be the first structurally authenticated terminal magnesium hydride complex. Although attempts to prepare [(MesNacnac)Mg(,-H)2Mg(MesNacnac)] were not successful, a neutron diffraction study of the corresponding magnesium(I) complex, [(MesNacnac)MgMg(MesNacnac)] confirmed that the compound is devoid of hydride ligands. [source]

Origin of the formation of the 4-butenyl end group in zirconocene-catalyzed propylene polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2006
Bernabe Quevedo-Sanchez
It has been proposed that the 4-butenyl end group in polypropylene is formed by isomerization of the 2-butenyl end group. Prior experimental evidence has shown that the isomerization is not produced thermally or upon an acidic treatment during the workup or analysis of the polymer. We postulate that the production of the 4-butenyl end group by isomerization might be catalyzed by a zirconocene hydride complex that forms during the ,-hydride elimination reaction. The isomerization of a preformed olefinic-end-group isotactic polypropylene with a well-known transition-metal hydride shows the disappearance of the 2-butenyl end group concomitant with the appearance of the 4-butenyl end group. [source]

Phosphine Ligands in the Palladium-Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP,NMR Spectroscopic Study

CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010
Verónica de, la Fuente Dipl.-Chem.
Abstract Novel cis -1,2-bis(di- tert -butyl-phosphinomethyl) carbocyclic ligands 6,9 have been prepared and the corresponding palladium complexes [Pd(O3SCH3)(L-L)][O3SCH3] (L- L=diphosphine) 32,35 synthesised and characterised by NMR spectroscopy and X-ray diffraction. These diphosphine ligands give very active catalysts for the palladium-catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9, containing four- and six-membered ring backbones giving more active systems. The acid used as co-catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O3SCH3)(L- L)][O3SCH3], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism. [source]

,-Diketiminate-Stabilized Magnesium(I) Dimers and Magnesium(II) Hydride Complexes: Synthesis, Characterization, Adduct Formation, and Reactivity Studies

Hydrocarbon-Soluble Calcium Hydride: A "Worker-Bee" in Calcium Chemistry

CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2007
Jan Spielmann
Abstract The reactivity of the hydrocarbon-soluble calcium hydride complex [{CaH(dipp-nacnac)(thf)}2] (1; dipp-nacnac=CH{(CMe)(2,6- iPr2C6H3N)}2) with a large variety of substrates has been investigated. Addition of 1 to CO and CN functionalities gave easy access to calcium alkoxide and amide complexes. Similarly, reduction of the CN bond in a cyanide or an isocyanide resulted in the first calcium aldimide complexes [Ca{NC(H)R}(dipp-nacnac)] and [Ca{C(H)NR}(dipp-nacnac)], respectively. Complexation of 1 with borane or alane Lewis acids gave the borates and alanates as contact ion pairs. In reaction with epoxides, nucleophilic ring-opening is observed as the major reaction. The high reactivity of hydrocarbon-soluble 1 with most functional groups contrasts strongly with that of insoluble CaH2, which is essentially inert and is used as a common drying agent. Crystal structures of the following products are presented: [{Ca{OC(H)Ph2}(dipp-nacnac)}2], [{Ca{NC(H)Ph}(dipp-nacnac)}2], [{Ca{C(H)NC(Me)2CH2C(Me)3}(dipp-nacnac)}2], [{Ca{C(H)NCy}(dipp-nacnac)}2], [Ca(dipp-nacnac)(thf)]+[H2BC8H14], and [{Ca(OCy)(dipp-nacnac)}2]. The generally smooth and clean conversions of 1 with a variety of substrates and the stability of most intermediates against ligand exchange make 1 a valuable key precursor in the syntheses of a wide variety of ,-diketiminate calcium complexes. [source]

Hydrogen/Deuterium Exchange Reactions of Olefins with Deuterium Oxide Mediated by the Carbonylchlorohydrido- tris(triphenylphosphine)ruthenium(II) Complex

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010
Sunny Kai San Tse
Abstract The catalytic properties of several ruthenium, osmium and rhodium hydride complexes for hydrogen/deuterium (H/D) exchange between olefins and deuterium oxide (D2O) were investigated. The most effective catalytic precursor was found to be the carbonylchlorohydridotris(triphenylphosphine)ruthenium(II) complex. Through H/D exchange between metal hydride and D2O, and reversible olefin insertion into an RuH(D) bond, protons attached to olefinic carbons and alkyl chains of olefins can all undergo H/D exchange with D2O. The catalytic reactions can be used to deuterate both terminal and internal olefins, for example, styrene, stilbene and cyclooctene. [source]

Efficient Functionalisation of Cubic Monovinylsilsesquioxanes via Cross-Metathesis and Silylative Coupling with Olefins in the Presence of Ruthenium Complexes

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009
Patrycja
Abstract Monovinylheptaisobutylsilsesquioxane undergoes efficient cross-metathesis and silylative coupling with styrenes. Allyl derivatives were successfully tested in cross-metathesis in the presence of first generation Grubbs' catalyst, while heteroatom-substituted vinyl derivatives (vinyl ethers, 9-vinylcarbazole) efficiently undergo silylative coupling catalysed by ruthenium hydride complexes. Both reactions proceed highly stereoselectively and lead to nearly quantitative formation of E isomers. Only when vinyl ethers are used does the reaction lead to a mixture of stereoisomers. Atmospheric pressure photoionisation has been successfully used for recording mass spectra of the functionalised silsesquioxanes. [source]

Why Platinum Catalysts Involving Ligands with Large Bite Angle Are so Efficient in the Allylation of Amines: Design of a Highly Active Catalyst and Comprehensive Experimental and DFT Study

CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2008
Guilhem Mora
Abstract The platinum-catalyzed allylation of amines with allyl alcohols was studied experimentally and theoretically. The complexes [Pt(,3 -allyl)(dppe)]OTf (2) and [Pt(,3 -allyl)(DPP-Xantphos)]PF6 (5) were synthesized and structurally characterized, and their reactivity toward amines was explored. The bicyclic aminopropyl complex [Pt(CH2CH2CH2NHBn- , - C,N)(dppe)]OTf (3) was obtained from the reaction of complex 2 with an excess of benzylamine, and this complex was shown to be a deactivated form of catalyst 2. On the other hand, reaction of complex 5 with benzylamine and allyl alcohol led to formation of the 16-VE platinum(0) complex [Pt(,2 -C3H5OH)(DPP-Xantphos)] (7), which was structurally characterized and appears to be a catalytic intermediate. A DFT study showed that the mechanism of the platinum-catalyzed allylation of amines with allyl alcohols differs from the palladium-catalyzed process, since it involves an associative ligand-exchange step involving formation of a tetracoordinate 18-VE complex. This DFT study also revealed that ligands with large bite angles disfavor the formation of platinum hydride complexes and therefore the formation of a bicyclic aminopropyl complex, which is a thermodynamic sink. Finally, a combination of 5 and a proton source was shown to efficiently catalyze the allylation of a broad variety of amines with allyl alcohols under mild conditions. [source]