Verónica Salazar
Universidad Autónoma del Estado de Hidalgo
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Dalton Transactions | 2013
Martín Hernández‐Juárez; Mónica Vaquero; Eleuterio Álvarez; Verónica Salazar; Andrés Suárez
The preparation of new Ru(II) complexes incorporating fac-coordinated lutidine-derived CNC ligands is reported. These derivatives are selectively deprotonated by (t)BuOK at one of the methylene arms of the pincer, leading to catalytically active species in the hydrogenation of imines.
Chemistry: A European Journal | 2015
Martín Hernández‐Juárez; Joaquín López-Serrano; Patricia Lara; Judith P. Morales-Cerón; Mónica Vaquero; Eleuterio Álvarez; Verónica Salazar; Andrés Suárez
A series of Ru complexes containing lutidine-derived pincer CNC ligands have been prepared by transmetalation with the corresponding silver-carbene derivatives. Characterization of these derivatives shows both mer and fac coordination of the CNC ligands depending on the wingtips of the N-heterocyclic carbene fragments. In the presence of tBuOK, the Ru-CNC complexes are active in the hydrogenation of a series of imines. In addition, these complexes catalyze the reversible hydrogenation of phenantridine. Detailed NMR spectroscopic studies have shown the capability of the CNC ligand to be deprotonated and get involved in ligand-assisted activation of dihydrogen. More interestingly, upon deprotonation, the Ru-CNC complex 5 e(BF4 ) is able to add aldimines to the metal-ligand framework to yield an amido complex. Finally, investigation of the mechanism of the hydrogenation of imines has been carried out by means of DFT calculations. The calculated mechanism involves outer-sphere stepwise hydrogen transfer to the C-N bond assisted either by the pincer ligand or a second coordinated H2 molecule.
Chemistry: A European Journal | 2013
Crispín Cristóbal; Yohar A. Hernández; Joaquín López-Serrano; Margarita Paneque; Ana Petronilho; Manuel L. Poveda; Verónica Salazar; Florencia Vattier; Eleuterio Álvarez; Celia Maya; Ernesto Carmona
The reactivity of a series of iridiumpyridylidene complexes with the formula [Tp(Me2) Ir(C6 H5 )2 (C(CH)3 C(R)NH] (1 a-1 c) towards a variety of substrates, from small molecules, such as H2 , O2 , carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e(-) unsaturated [Tp(Me2) Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H2 is heterolytically split to give hydridepyridylidene complexes, whilst CO, CO2 , and H2 CO provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five-membered metallacycles with an IrCH2 CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four-membered iridacycles with the IrC(CH2 )N moiety. C6 H5 (CO)H and C6 H5 CCH react with formation of IrC6 H5 and IrCCPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a-1 c against O2 is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.
Chemistry: A European Journal | 2009
Patricia Lara; Margarita Paneque; Manuel L. Poveda; Laura L. Santos; José E. Villar Valpuesta; Verónica Salazar; Ernesto Carmona; Salvador Moncho; Gregori Ujaque; Agustí Lledós; Celia Maya; Kurt Mereiter
Experimental and theoretical studies on equilibria between iridium hydride alkylidene structures, [(Tp(Me2))Ir(H){=C(CH(2)R)ArO}] (Tp(Me2) = hydrotris(3,5-dimethylpyrazolyl)borate; R = H, Me; Ar = substituted C(6)H(4) group), and their corresponding hydride olefin isomers, [(Tp(Me2))Ir(H){R(H)C=C(H)OAr}], have been carried out. Compounds of these types are obtained either by reaction of the unsaturated fragment [(Tp(Me2))Ir(C(6)H(5))(2)] with o-C(6)H(4)(OH)CH(2)R, or with the substituted anisoles 2,6-Me(2)C(6)H(3)OMe, 2,4,6-Me(3)C(6)H(2)OMe, and 4-Br-2,6-Me(2)C(6)H(2)OMe. The reactions with the substituted anisoles require not only multiple C-H bond activation but also cleavage of the Me-OAr bond and the reversible formation of a C-C bond (as revealed by (13)C labeling studies). Equilibria between the two tautomeric structures of these complexes were achieved by prolonged heating at temperatures between 100 and 140 degrees C, with interconversion of isomeric complexes requiring inversion of the metal configuration, as well as the expected migratory insertion and hydrogen-elimination reactions. This proposal is supported by a detailed computational exploration of the mechanism at the quantum mechanics (QM) level in the real system. For all compounds investigated, the equilibria favor the alkylidene structure over the olefinic isomer by a factor of between approximately 1 and 25. Calculations demonstrate that the main reason for this preference is the strong Ir-carbene interactions in the carbene isomers, rather than steric destabilization of the olefinic tautomers.
Journal of Organometallic Chemistry | 1997
Enrique Gutiérrez; M. Carmen Nicasio; Margarita Paneque; Caridad Ruiz; Verónica Salazar
Abstract The complex PdCl2(cod) (cod = 1,4-cyclooctadiene) reacts with one equivalent of R(Mg)Cl (R = CH2CMe2Ph, CH2SiMe3, CH2C6H4-o-Me) to yield monoalkyl derivatives of composition Pd(R)Cl(cod). The cyclooctadiene ligand is readily displaced by dmpe (dmpe = 1,2-bis(dimethylphosphino)ethane) and PMe3 to generate Pd(R)Cl(L2) (L2 = (PMe3)2, dmpe) of which, the complex Pd(CH2CMe2Ph)Cl(PMe3)2 thermally isomerizes to the palladium aryl Pd(C6H4-o-CMe3)Cl(PMe3)2 in the presence of catalytic amounts of NEt3. Carbonylation of the alkyl derivatives affords acyl complexes Pd(COR)Cl(L2) and related iminoacyl derivatives have also been obtained by the analogous reaction with tert-butyl-isocyanide. New alkyl and acyl species containing bis(pyrazolyl)borate ligands have been prepared by halide metathesis in the Pd(R/COR)Cl(PMe3)2 complexes. During the course of these reactions one equivalent of PMe3 is liberated. The complex Bp∗Pd(CH2SiMe3)(PMe3) has been structurally characterized by X-ray crystallography.
Chemistry: A European Journal | 2011
Yohar A. Hernández; Joaquín López-Serrano; Margarita Paneque; Manuel L. Poveda; Florencia Vattier; Verónica Salazar; Eleuterio Álvarez; Ernesto Carmona
Generation of a C N bond by tandem oxidative dehydrogenation of aromatic C H and N H units is an important process in modern organic synthesis. Oxygen is the preferred reagent for this purpose, usually in combination with Cu catalysts, although other common oxidants can be employed. Herein, we wish to report that oxygen is able to promote dehydrogenative C N coupling of phenyl and NH pyridylidene coligands of some Tp2Ir complexes (Tp2 = hydrotris(3,5-dimethylpyrazolyl)borate). It is known that 2-substituted pyridines react with the Ir complex [TpMe2IrACHTUNGTRENNUNG(C6H5)2(N2)] (1), to form NH-pyridylidenes, [TpMe2IrACHTUNGTRENNUNG(C6H5)2ACHTUNGTRENNUNG(=CN(H)C4(R)H3)] (2 ; R= Me, Ph, tBu, etc.). In contrast, the reaction with pyridine yields instead an N adduct that is stable up to 150 8C. Nonetheless, following recent work by Lewis, Bergman, and Ellman, we have now prepared the parent pyridylidene 2 a (R=H) by alkaline hydrolysis of the new carbene derived from 2-(trimethylsilyl)pyridine. Since it is also known that carbenes 2 b (R=Me) and 2 c (R=Ph) react with CO and unsaturated hydrocarbons (e.g., C2H2, C2H4, and C3H6) through reversible generation of unsaturated pyridyl intermediate A (Scheme 1), we regarded it as worthwhile to investigate the reactivity of carbenes 2 a–c towards oxygen. Under the conditions specified in Scheme 2 (C6H6, 90 8C), oxidation of compounds 2 by O2 provides mixtures of complexes 3 and 4 in the following ratios: 3 a/4 a= 1:2; 3 b/4 b= 3 c/4 c= 1:1. Complexes 3 and 4 form through independent pathways and even though the ratios of 3/4 are not affected significantly by variation of the O2 pressure (from air (1 atm) to O2 (4 atm)), they display a remarkable dependence on temperature. Thus, at 60 8C, the now slower reactions strongly favor the C N coupling products, as revealed by the ratios of compounds 3/4 : 3 a/4 a=1:10; 3 b/4 b=3 c/ 4 c=3:10. All new compounds have been characterized by analytical and spectroscopic data and the structures proposed have, in addition, been authenticated by X-ray crystallography studies carried out with 3 b and 4 b. Compounds 3 are best described as derivatives of 2-metallated pyridine-N-oxide ligands coordinated to iridium in a k-C,O fashion. Formation of these species is probably a result of the incorporation of an oxygen atom into intermediate A (Scheme 1) in a process assisted by the metal center. In turn, compounds 4 stem from oxidative dehydrogenation of the carbene N H bond and a phenyl ortho C H bond, with concomitant formation of a C N bond. Figure 1 shows the X-ray crystal structure of 3 b, which, to the best of our knowledge, has no precedent among the d-block transition metals. The Ir C carbene bond length (1.998(3) ) is similar to that found in related cyclic pyridylidenes. An ORTEP structure of complex 4 b is shown in Figure 2, with the two aromatic rings in the newly formed ligand being, as expected, almost coplanar. [a] Dr. Y. A. Hern ndez, Dr. J. L pez-Serrano, Prof. Dr. M. Paneque, Prof. Dr. M. L. Poveda, F. Vattier, Dr. E. lvarez, Prof. Dr. E. Carmona Instituto de Investigaciones Qu micas and Dpto. Qu mica Inorg nica Consejo Superior de Investigaciones Cient ficas and Universidad de Sevilla Av. Am rico Vespucio, 49, 41092-Sevilla (Spain) Fax: (+34) 95-446-0565 E-mail : [email protected] [b] Dr. V. Salazar Centro de Investigaciones Qu micas Universidad Aut noma del Estado de Hidalgo Carretera Pachuca a Tulancingo, Pachuca, Hidalgo (Mexico) [**] Tp2 =hydrotris(3,5-dimethylpyrazolyl)borate Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201101276. Scheme 1. Reversible formation of species A from 2.
Chemical Communications | 2004
Margarita Paneque; Manuel L. Poveda; Laura L. Santos; Verónica Salazar; Ernesto Carmona
The in situ generated [Tp(Me2)Ir(C(6)H(5))(2)] fragment induces both aromatic and aliphatic C-H bond activation reactions, along with C-C bond formation, when heated with benzene and 1,2-dimethoxyethane.
Journal of the American Chemical Society | 2003
Margarita Paneque; Cristina M. Posadas; Manuel L. Poveda; Nuria Rendón; Verónica Salazar; Enrique Oñate; Kurt Mereiter
Organometallics | 2007
Margarita Paneque; Cristina Martín-Posadas; Manuel L. Poveda; Nuria Rendón; Laura L. Santos; Eleuterio Álvarez; Verónica Salazar; Kurt Mereiter; Enrique Oñate
Angewandte Chemie | 2008
Salvador Conejero; Patricia Lara; Margarita Paneque; Ana Petronilho; Manuel L. Poveda; Oracio Serrano; Florencia Vattier; Eleuterio Álvarez; Celia Maya; Verónica Salazar; Ernesto Carmona