RESUMO
A new protocol for the direct cobalt-catalyzed vinylation of aryl halides using ß-halostyrene has been developed in order to form functionalized stilbenes. A variety of aromatic halides featuring different reactive group were employed. This method proceeded smoothly with a total retention of the double bond configuration in the presence of triphenylphosphine as ligand. Preliminary DFT calculations rationalize these results and proposed a reaction pathway in agreement with the experimental conditions. This procedure offers a new route to the stereoselective synthesis of stilbenes.
Assuntos
Cobalto/química , Hidrocarbonetos Halogenados/química , Estilbenos/síntese química , Estirenos/química , Catálise , Ligantes , Estrutura Molecular , Estereoisomerismo , Estilbenos/químicaRESUMO
The catalytic activity both of cationic [(XDPP)Au][X] (XDPP = bis-2,5-diphenylphosphole xantphos X = BF(4)) and of the isolated gold hydride complex [(XDPP)(2)Au(2)H][OTf] in the dehydrogenative silylation process is presented. A parallel theoretical study using density functional theory revealed a mechanism involving the counter anion as a co-catalyst, which was experimentally confirmed by testing various counterions (X = OTf, NTf(2), PF(6)). Finally, a "Au(2)H(+)" species was determined as the intermediate during the catalytic cycle, which correlates well with the experimental findings on the first example of catalytic activity of an isolated "Au-H" complex.
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Using a geminal dianion as precursor, a nucleophilic scandium carbene complex (2) has been synthesized by salt metathesis on ScCl(3)(THF)(3) in 52% isolated yield. The X-ray structure as well as an NBO analysis points to a double interaction between the carbon and the scandium atoms. Quantification of the electron density donation from the carbon to the metal center, from both σ and π symmetry orbitals, predicts a "nucleophilic carbene" behavior. Addition of benzophenone on complex 2 results in the formation of the expected alkene derivative and the trapping of a rare, µ(3)-oxo-Sc species via a "scandia-Wittig" reaction.
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In this article, we present a critical study of the theoretical protocol used for the determination of the nickel(II) catalyzed ethylene dimerization mechanism, considered as a representative example of the various problems related to the modeling a catalytic cycle. The choice of an appropriate computational procedure is indeed crucial for the validity of the conclusions that will be drawn from the computational process. The influence of the exchange-correlation functional on energetic profiles and geometries, the role of the basis set describing the metal atom, as well as the importance of the chosen molecular model, have been thus examined in details. From the obtained results, some general conclusions and guidelines are presented, which could constitute useful warnings in modeling homogenous catalysis. Besides, the database constituted by our high-level calculations can be used within benchmarking procedures to assess the performances of new computational methods based on density functional theory.
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The synthetic outcome of the Friedel-Crafts acylation of 1',2',3,3',4,4',5'-heptamethylphospharuthenocene reflects the nature of the acylating agent, with alkanoyl anhydride/trifluoromethanesulfonic acid (TfOH) reagents giving monosubstitution at the phospholyl ring, whereas alkanoyl chloride/AlCl(3) gives 2,5-disubstitution. DFT calculations indicate that this unusual double acylation can be facilitated by the intervention of the phosphorus atom at an early stage in the reaction trajectory, with the acyl group being delivered from the phosphorus atom into the ring 2- or 2,5-positions.
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This work describes the synthesis of three key intermediates of Noyori-type catalytic systems that are active precatalysts for the transfer hydrogenation of acetophenone. Isolation of the cationic chloro(dihydrogen) complex [RuCl(H(2))(H(2)NNPP)(PCy(3))][BArf(4)] provides a facile synthetic route to the corresponding cationic and neutral hydrido complexes, and the series highlights the links between hydride/dihydrogen and amine/amido ligands in neutral and cationic species.
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Treatment of U(BH(4))(4) with 1 or 3 equiv of Li(2)(SCS) x 1.5 Et(2)O, 1, afforded the actinide carbene complexes U(mu-SCS)(3)[U(BH(4))(3)](2) (4) and U(mu-SCS)(3)[Li(Et(2)O)](2) (6), respectively [SCS = (Ph(2)P = S)(2)C]. In THF, complex 4 was transformed into the mononuclear derivative (SCS)U(BH(4))(2)(THF)(2) (5). The multiple bond character of the uranium-carbon bond was first revealed by the X-ray crystal structures of the three complexes. The U=C bond in these complexes present a nucleophilic character, as shown by their reaction with a carbonyl derivative. Finally, DFT calculations prove the involvement of both 5f and 6d orbitals in both the sigma and the pi U-C bonds.
RESUMO
Effective devotion: An efficient cobalt-catalyzed method devoted to the formation of symmetrical biaryls is described avoiding the preparation of organometallic reagents. Various aromatic halides functionalized by a variety of reactive group reagents are employed. Preliminary DFT calculations have shown that the involvement of a Co(I)/Co(III) couple is realistic at least in the case of 1,3-diazadienes as ligands (FG = functional group).
Assuntos
Compostos de Bifenilo/síntese química , Cobalto/química , Alcenos/química , Compostos Aza/química , Compostos de Bifenilo/química , Catálise , Hidrocarbonetos Halogenados/síntese química , Hidrocarbonetos Halogenados/química , Ligantes , Modelos Moleculares , Teoria QuânticaRESUMO
Chromium(III) complexes bearing R'N(CH2PR2)2 (PCNCP) ligands have been prepared. Upon activation with methylaluminoxane, these complexes proved to be effective in the selective tri- and tetramerization of ethylene. The formation of either 1-hexene or 1-octene was found to be highly dependent on the steric bulk of the substituents R on the phosphine moieties. This observation was rationalized by using density functional theory calculations on selected steps of the metallacyclic mechanism of the ethylene oligomerization reaction.
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A bulky 1-phosphabarrelene, , was obtained from the reaction of a phosphinine with benzyne; two palladium complexes of were successfully employed in the Suzuki-Miyaura coupling of several aryl chlorides with phenylboronic acid at a relatively low catalyst loading, and activated aryl chlorides were coupled at room temperature in the absence of strong bases.
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Protonation of a bidentate xantphos-phosphole ligand by HBF(4) affords only one enantiomer of a cyclic phospholium dihydropholene structure. DFT calculations allowed us to establish that protonation initially takes place at the phosphorus atom of the phosphole moiety to afford a transient P-H phospholium salt, which in turn protonates the C=C double bond of the second phosphole unit.
RESUMO
The bis-2,5-diphenylphosphole xantphos ligand (XDPP) 1 reacts with the [AuCl(tht)] complex to afford the monocoordinated [Au(XDPP)Cl] 2 and the dicoordinated chelate species [Au(XDPP)Cl] 3. Addition of AgOTf on this mixture, at room temperature, affords the cationic [Au(XDPP)][OTf] complex 4 which was fully characterized. An X-ray crystal structure analysis confirms the bent structure of this 14 VE [ML(2)](+) complex. Reaction of 4 with HSiMe(2)Ph in tetrahydrofuran at -78 degrees C yields the dinuclear [(XDPP)Au-H-Au(XDPP)](+) cationic complex 5, in which the hydride bridges the two [Au(XDPP)](+) metal fragments. In 5, the Au-P bond lengths are different and the phosphorus atoms which are located nearly trans to the hydride ligand exhibit significantly shorter P-Au bond lengths. Reaction of 4 with DSiMe(2)Ph to form the [(XDPP)Au-D-Au(XDPP)](+) complex 6 allowed to unambiguously ascribe the chemical shift of the deuteride in (2)H NMR (delta = 7.0 ppm with a (2)J(DP) = 8.4 Hz. The electronic structure of the [(XDPP)Au-H-Au(XDPP)](+) complex was studied through density functional theory calculations. An orbital analysis is developed in which complex 5 is viewed as the combination of two 12 electrons fragments [Au(XDPP)](+) with H(-). This analysis reveals that the hydride interacts in a bonding way with the sigma MO between the two gold atoms and in an antibonding way with a combination of d orbitals at the metal centers. This simple description allows to rationalize the inequivalence of the two types of P-Au bonds in 5.
RESUMO
The platinum-catalyzed allylation of amines with allyl alcohols was studied experimentally and theoretically. The complexes [Pt(eta(3)-allyl)(dppe)]OTf (2) and [Pt(eta(3)-allyl)(DPP-Xantphos)]PF(6) (5) were synthesized and structurally characterized, and their reactivity toward amines was explored. The bicyclic aminopropyl complex [Pt(CH(2)CH(2)CH(2)NHBn-kappa-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(eta(2)-C(3)H(5)OH)(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.
Assuntos
Compostos Alílicos/química , Aminas/química , Catálise , Compostos Organoplatínicos/síntese química , Platina/química , Teoria Quântica , Ligantes , Estrutura MolecularRESUMO
White phosphorus, P4, was reacted in a stoichiometric manner with Ni(0) complexes or particles to produce nanoparticles of nickel phosphide.
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A new type of stable radical ligand featuring a 1,1-bis-phosphinosulfide alkene backbone has been prepared and characterized on the basis of X-ray diffraction, EPR and DFT studies.
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The phosphinosilane compound PPh 2CH 2OSiMe 2H is potentially a bifunctional P approximately Si-H ligand. By treatment with the Ru (II) precursor RuH 2(H 2) 2(PCy 3) 2, the complex Ru(PPh 2CH 2OSiMe 2H) 3 ( 2), resulting from the coordination of three ligands and the displacement of two PCy 3 and two dihydrogen ligands, was formed. The different bonding modes for each of the three bifunctional P approximately Si-H ligands are discussed on the basis of multinuclear NMR, X-ray diffraction, and density functional theory studies. One ligand acts as a monodentate phosphine ligand with a pendant Si-H group, whereas the two others act as bidentate ligands with different Si-H bond activations. Indeed, an intermediate structure between two arrested forms 2a and 2b can be proposed: a dihydrido(disilyl)ruthenium(IV) species (form 2a) resulting from two Si-H oxidative additions or a hydrido(silyl)ruthenium(II) species (form 2b) presenting an agostic Si-H bond and only one oxidative addition.
RESUMO
Regioselectivity increases in C=C double bond hydrogenation could be obtained for Lewis basic substrates on a Lewis acidic support by using a rhodium complex supported on a mesoporous solid.
Assuntos
Carbono/química , Ródio/química , Monoterpenos Acíclicos , Compostos Bicíclicos com Pontes/química , Catálise , Domínio Catalítico , Ciclização , Hidrogenação , Ligantes , Estrutura Molecular , Estereoisomerismo , Especificidade por Substrato , Terpenos/químicaRESUMO
Zirconia-silica mesoporous powders act as very efficient heterogeneous catalysts for both alkyne hydroformylation and Pauson-Khand reaction and yield regioselectivities opposite to those usually observed.
Assuntos
Alcinos/síntese química , Compostos Organometálicos/química , Dióxido de Silício/química , Zircônio/química , Alcinos/química , Catálise , Estrutura Molecular , Porosidade , Pós/química , EstereoisomerismoRESUMO
A highly rigid dibenzo[a,d]cycloheptenyl dibenzophosphole with a pre-organized concave shaped binding site acts as an efficient ligand in the palladium catalyzed Suzuki-Miyaura coupling process between halogenoaromatics and phenylboronic acid.