3,345 research outputs found
Alkylamino imidazolium aurate salts: synthesis, structures and applications
No full textWe have recently described the synthesis and characterization of amino-functionalized N-heterocyclic carbene complexes of silver(I), Ag(I)-NHCs, using the Boc-protected and deprotected 1-(2-aminoethyl)-3-methyl imidazolium salts [NH2(CH2)2ImMe]X, [1]X (X = I, PF6) as carbene precursors [1].
We are now presenting the preparation of a new gold(III)-alkylamino imidazolium aurate salt [Cl3AuNH2(CH2)2ImMe)][AuCl4] (2). Demonstrating the great versatility of the amino-functionalized imidazolium salts, such compound is an useful precursor for the preparation of gold nanoparticle (AuNPs) films via the layer-by-layer (LBL) assembly method [2]. Assembling appropriate polyelectrolytes such as poly(ethyleneimine) (PEI) on Indium Tin Oxide Glasses (ITO) a monolayer film of 2 can be easily grafted on the surface and after subsequent reduction, well controlled, in size and distribution, immobilized AuNPs can be generated. The morphology of the AuNPs layers was investigated by using AFM and SEM microscopy and X-ray diffraction (XRD).
References
[1] L. Busetto, M.C. Cassani, C. Femoni, A. Macchioni, R. Mazzoni, D. Zuccaccia, J. Organomet. Chem. 693, 2579 (2008).
[2] J.F. Quinn, A.P.R. Johnston, G.K. Such, A.N. Zelikin, F. Caruso, Chem. Soc. Rev. 36, 707 (2007)
Noncooperative oligopoly in markets with a continuum of traders
No full textIn this paper, we study three prototypical models of noncooperative oligopoly in markets with a continuum of traders : the model of Cournot-Walras equilibrium of Codognato and Gabszewicz (1991), the model of Cournot-Nash equilibrium of Lloyd S. Shapley, and the model of Cournot-Walras equilibrium of Busetto et al. (2008). We argue that these models are all distinct and only the Shapley's model with a continuum of traders and atoms gives an endogenous explanation of the perfectly and imperfectly competitive behavior of agents in a one-stage setting. For this model, we prove a theorem of existence of a Cournot-Nash equilibrium
Noncooperative Oligopoly in Markets with a Continuum of Traders
No full textIn this paper, we study three prototypical models of noncooperative oligopoly in markets with a continuum of traders : the model of Cournot-Walras equilibrium of Codognato and Gabszewicz (1991), the model of Cournot-Nash equilibrium of Lloyd S. Shapley, and the model of Cournot-Walras equilibrium of Busetto et al. (2008). We argue that these models are all distinct and only the Shapley's model with a continuum of traders and atoms gives an endogenous explanation of the perfectly and imperfectly competitive behavior of agents in a one-stage setting. For this model, we prove a theorem of existence of a Cournot-Nash equilibrium.
Selective formation of one or two C-C bonds promoted by carbanion addition to [Fe2(cp)2(CO)2(μ-CO)(μ-CSMe)]+
No full textThe reactions of [Fe2(cp)2(CO)2(μ-CO)(μ-CSMe)]CF 3SO3 (1; cp = η-C5H5) with a variety of carbon nucleophiles result in C-C bond formation at different sites of the molecule, (allyl)-MgCl (allyl = C3H5) undergoes cp addition to form [Fe2(cp)(η4-C5H5-allyl)(CO) 2(μ-CO)(μ-CSMe)] (2) and the alkylidene complex [Fe2(cp)(η-C5H4-allyl) (CO)2(μ-CO){μ-C(SMe)H}] (3), derived from cp to μ-C hydrogen migration. Li2Cu(CN)R2 adds at the μ-C atom to yield [Fe2(cp)2(CO)2(μ-CO){μ-C(SMe)R}] (R = Ph, 4; R = Me, 8), [FeFe(cp)2(CO)(μ-CO){μ-C(SMe)R}] (R = Ph, 5; R = Me, 9), and [Fe2(cp)2(CO)(μ-CO){μ-C(ηl2-Ph)Ph}] (6) or the vinylidene derivative [Fe2(cp)2(CO)(μ-CO)(μ-C=CH2)] (10) in the case of phenyl or methyl organocuprate reagents, respectively. The latter complexes are the result of C-SMe bond breaking occurring, through different reaction paths, in 4 and 8. Likewise, the formation of [Fe2-(cp)2(CO)(μ-CO){μ-C=C(CN)2}] (11) from 1 and NaCH(CN)2 occurs via a direct addition at the μ-C carbon followed by HSMe elimination. The nucleophilic attack at the terminal CO in 1 is achieved with LiC≡CPh, which forms two new C-C bonds in the alkylidene complex [FeFe(cp)2(CO)(μ-CO){μ-C(SMe)C(O)CCPh}] (12) after C(O)CCPh migration from Fe to the bridging carbene carbon. The analogous [FeFe(cp)2(CO)(μ-CO)(μ-C(SMe)C(O)(2-th)}] (13; 2-th = 2-C4H3S) and [Fe2(cp)(η4-C5H5-(2-th)(CO) 2(μ-CO)(μ-CSMe)] (14) are obtained from 1 and Lith via addition at the CO and cp groups, respectively. The relevance of these reactions is discussed in terms of selective C-C bond formation that, if it occurs at the cp or CO terminal ligands, favors the hydrogen migration (e.g. formation of 3) or the carbyne-carbonyl migratory coupling (e.g. formation of 12 and 13), respectively. The X-ray structures of [Fe2-(cp)2(CO)(μ-CO){μ-C(η2-Ph)Ph}] (6) and [FeFe(cp)2(CO)(μ-CO){μ-C(SMe)C(O)(2-th)}] (13) have revealed the peculiarity of the Ph and SMe group coordination to the iron. Their structural features are discussed in comparison with those of analogous complexes. © 1997 American Chemical Society
Alkylamino Imidazolium salts as NHC carbene precursors and metal nanoparticles stabilizers
No full textThe synthesis of the Boc-protected 1-(2-NHBoc-ethyl)-3-R-imidazolin-2-ylidene, NHBociy, (R = Me, (1a), allyl (1b), benzyl, (1c)) and their straightforward transformation into the deprotected NH2iy (2a-c) is reported. The salts [1]X and [2]X (X = I, Br, PF6, BF4, NO3) are all viscous liquids at room temperature and can be considered as ionic liquids (ILs)1 whereas the tetrachloroaurate salts are yellow solids.
Imidazolium salts are typical N-Heterocyclic carbene (NHCs) precursor2 and the reaction with Ag2O leads to the formation of silver carbenes Ag(I)-NHCs presenting in the solid state different bonding motifs determined by X-ray diffraction analysis, whereas PGSE NMR experiments were employed to investigate the hydrodynamic dimension of the imidazolium salts and silver complexes and, consequently, to gain information on the level of aggregation in solution. PGSE NMR studies were complemented by NOE NMR investigations in order to obtain information on anion-cation relative orientation within aggregates.3 Rh(I)- and Pd(II)-NHC complexes were obtained either by i) direct deprotonation of the imidazolium salts with suitable metal precursors or ii) by using the silver complexes as transmetallating agents; properties of the resulting complexes were studied with NMR spectroscopy and X-ray crystallography.
Alongside with the NHC research line described above we have started to investigate the role of 2 as stabilizers for the synthesis of gold and silver nanoparticles and in the second part of this contribution preliminary results concerning this topic will be presented.4,5
[1] Wasserscheid, P.; Welton, T. (Ed.), Ionic Liquids in Synthesis, Wiley-VCH, Weinheim, Germany, 2002, p. 1.
[2] Crabtree, R.H. Coord. Chem. Rev. 2007, 251, 595 ff.: a volume completely dedicated to recent developments in the organometallic chemistry of N-heterocyclic carbenes.
[3] Busetto, L.; Cassani, M.C.; Femoni, C.; Macchioni, A.; Mazzoni, R.; Zuccaccia, D. J.Organomet.Chem. 2008 in press.
[4] Dahl, J.A.; Maddux, B.L.S.; Hutchinson, J.E. Chem. Rev. 2007, 107, 2228.
[5] Ballarin, B.; Cassani, M.C.; Scavetta, E.; Tonelli, D. Electroch. Acta 2008 in press
Formation of C-C bonds in diiron complexes by carbanions addition to alkynyl(methoxy)carbene ligands
No full textAddition of cyanide ions to the alkynyl(methoxy)carbene complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CO){Cα(OMe)Cβ≡CγR'}(Cp)2]+ (R = Xyl, R' = Tol, 1a; R = Xyl, R' = Ph, 1b; R = Xyl, R' = Me3Si, 1c; R = Me, R' = Tol, 1d; R = Me, R' = Ph, 1e) occurs selectively at Cα to afford the 1,1-disubstituted σ-propargyl complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CO){C(OMe)(CN)(C≡CR')}(Cp)2] (R = Xyl, R' = Tol, 2a; R = Xyl, R' = Ph, 2b; R = Xyl, R' = Me3Si, 2c; R = Me, R' = Tol, 2d; R = Me,R' = Ph, 2e). Conversely, the stabilised carbanaions[CH(R)2]– (R = CN, CO2Me) add at the Cγ position with subsequent hydrogen migration to Cβ to give the 1-σ-buta-1,3-dienyl complexes [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){Cα(OMe)=CβHCγ(Tol)=Cδ(R)2}(Cp)2] (R = CN, 3a; CO2Me, 3b). No migration is possible in the absence of hydrogen atoms at Cδ, therefore addition of [C(Me)(CO2Me)2]– to 1a results in the formation of the σ-allenyl complex [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){Cα(OMe)=Cβ=Cγ(Tol)Cδ(Me)(CO2Me)2}(Cp)2] (4). Protonation of the neutral complexes 3b and 4affords the vinyl(methoxy)carbene complexes [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){Cα(OMe)CβH=Cγ(Tol)Cδ(R)(CO2Me)2}]+ (R = H, 5; Me, 6), which exist in solution as mixtures of (E)- and (Z)-isomers in dynamic equilibrium, as shown by VT NMR studies. The cationic complex 6 shows electrophilic behaviour. Thus, addition of CN– results in the σ-allyl complex [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){Cα(OMe)(CN)[CβH=Cγ(Tol)Cδ(Me)(CO2Me)2]}(Cp)2] (7), whereas the reaction with Me2NH affords the vinyl acyl complex [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){Cα(O)CβH=Cγ(Tol)Cδ(Me)(CO2Me)2}(Cp)2] (8). The crystal structures of 2b and 3a·CH2Cl2 have been determined
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