Computational study of c-h bond cleavage and c-c bond formation processes catalyzed by transition metal complexes

La primera parte de la tesis se dedica al estudio del mecanismo de una reacción de activación C-H por un complejo de niobio. Se racionalizó el mecanismo de activación de enlaces C-H del benceno por el complejo TpMe2NbCH3(c-C3H5)(MeCCMe). El intermedio clave es un complejo inusual de 2-ciclopropeno. Conseguimos también racionalizar las selectividades obtenidas para la activación de varios alquilaromáticos por el complejo de niobio 2-ciclopropeno. También se investigó el papel del ligando alquino en estos complejos y su posible papel en procesos de migración de ligandos. En la segunda parte de la tesis, se investigaron las reacciones de acoplamiento cruzado con reactivos basados en silicio. Los resultados sugieren que la transmetalación es más fácil después de la disociación de la fosfina, o cuando un ligando bromuro está coordinado al paladio. El efecto beneficioso de la dibencilidenoacetona en el acoplamiento también fue aclarado.The first part of the thesis is mainly devoted to the mechanism of a C-H activation reaction by a niobium complex. The mechanism of C-H bond activation of benzene by the TpMe2NbCH3-(c-C3H5)-(MeCCMe) complex was rationalized. The key intermediate is an unusual 2-cyclopropene complex. We rationalized the selectivities obtained for the activation of several alkylaromatics by the 2-cyclopropene niobium complex. The intriguing role of the alkyne ligand of the same complex, and its possible role in the migration processes, was investigated. In the second part of the thesis, we focused on the silicon based cross-coupling. The results suggest than the transmetalation is easier after phosphine dissociation, and in presence of the bromide ligand on the palladium. The beneficial effect of dibenzylideneacetone on the coupling was clarified

Palladium catalysed sequential imine arylation/Suzuki–Miyaura coupling: synthesis of a-(biarylyl)benzylamines

report an innovative, high yielding one-pot sequential catalytic imine arylation/SuzukieMiyaura cross-coupling reaction, which converts suitably activated imine substrates to various biarylarylmethyl amine products using several commercial Pd catalysts. Many biarylarylmethyl amine molecules are biologically active. Insightful computational studies detail the mechanism of the imine arylation process. The sequence of reactions is likely to be dependent on the reaction conditions

A catalytic route to dibenzodiazepines involving Buchwald-Hartwig coupling: reaction scope and mechanistic consideration

We report a new synthetic method for the synthesis of a family of dibenzodiazepines (DBDAs), employing Pd-catalyzed C-N coupling of o-bromoaldimine, with o-bromoaniline as the key step. Eleven DBDAs were prepared, containing electron-withdrawing groups (CN, F, NO2) and electron-donating groups (OMe). The reaction conditions were optimized (catalyst, phosphine, base and solvent) and best results were obtained with Pd(OAc)(2), SPhos, Cs2CO3 in THF. Due to the ambiguity of the mechanism at hand, various mechanistic studies were performed, that included DFT calculations. The oxidative addition process was studied in detail by DFT, and these studies supported the observed reaction regioselectivity. The adducts formed between the aldimine and the Pd(0) catalyst were calculated to be more stable than the ones formed with the amine, and the barrier for the oxidative addition at the C-Br bond of the aldimine was calculated to be lower than the one at the C-Br bond of the aryl amine. The formation of DBDA over the dibenzoaminopiperidine has been explained in the final cyclization step

) Design and development of molecularly imprinted polymers for the selective extraction of deltamethrin in olive oil: an integrated computational-assisted approach

tThis work firstly addresses the design and development of molecularly imprinted systems selective fordeltamethrin aiming to provide a suitable sorbent for solid phase (SPE) extraction that will be furtherused for the implementation of an analytical methodology for the trace analysis of the target pesticidein spiked olive oil samples. To achieve this goal, a preliminary evaluation of the molecular recogni-tion and selectivity of the molecularly imprinted polymers has been performed. In order to investigatethe complexity of the mechanistic basis for template selective recognition in these polymeric matri-ces, the use of a quantum chemical approach has been attempted providing new insights about themechanisms underlying template recognition, and in particular the crucial role of the crosslinker agentand the solvent used. Thus, DFT calculations corroborate the results obtained by experimental molecu-lar recognition assays enabling one to select the most suitable imprinting system for MISPE extractiontechnique which encompasses acrylamide as functional monomer and ethylene glycol dimethacrylateas crosslinker. Furthermore, an analytical methodology comprising a sample preparation step based onsolid phase extraction has been implemented using this “tailor made” imprinting system as sorbent, forthe selective isolation/pre-concentration of deltamethrin from olive oil samples. Molecularly imprintedsolid phase extraction (MISPE) methodology was successfully applied for the clean-up of spiked olive oilsamples, with recovery rates up to 94%

Copper(I)−Olefin Complexes: The Effect of the Trispyrazolylborate Ancillary Ligand in Structure and Reactivity

9 páginas, 4 figuras, 5 tablas, 4 esquemas.The spectroscopic and structural characteristics and the relative reactivity of several TpMsCu(olefin) (olefin = ethylene, 1, 1-hexene, 2, allyl ethyl ether, aee, 3, cyclohexene, 4, and styrene, 5) complexes bearing the bulky hydrotris(3-mesitylpyrazolyl)borate ligand have been examined. Experimental data, including an unusual high-field chemical shift in the 1H and 13C NMR spectra, and DFT theoretical calculations support the proposal that the copper−olefin linkage is mainly sustained by σ-donation, lacking a substantial degree of π-back-donation.We thank the MICINN (Proyecto CTQ2008−00042BQU, CTQ2008-06866-CO2-02/BQU and Consolider Ingenio 2010 grant CSD2006-0003), the Junta de Andalucía (Proyecto P07-FQM-02794), and the ICIQ Foundation for financial support. C.M. thanks the Ministerio de Educación for a research fellowship.Peer reviewe

Chemo-, Regio-, and Stereoselective Silver-Catalyzed Aziridination of Dienes: Scope, Mechanistic Studies, and Ring-Opening Reactions

Silver complexes bearing trispyrazolylborate ligands (Tpx) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = p-toluensulfonyl) units from PhI=NTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the C=C bond is maintained in the aziridine product (cis or trans). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of ¿-amino alcohols have also been developed

β‑H Abstraction/1,3‑CH Bond Addition as a Mechanism for the Activation of CH Bonds at Early Transition Metal Centers

This article describes the generalization of an overlooked mechanism for CH bond activation at early transition metal centers, namely 1,3‑CH bond addition at an η²-alkene intermediate. The X-ray-characterized [Cp₂Zr­(<i>c</i>-C₃H₅)₂] eliminates cyclo­propane by a β‑H abstraction reaction to generate the transient η²-cyclo­propene [Cp₂Zr­(η²-<i>c</i>-C₃H₄)] intermediate <b>A</b>. <b>A</b> rapidly cleaves the CH bond of furan and thiophene to give the furyl and thienyl complexes [Cp₂Zr­(<i>c</i>-C₃H₅)­(2-C₄H₃X)] (X = O, S), respectively. Benzene is less cleanly activated. Mechanistic investigations including kinetic studies, isotope labeling, and DFT computation of the reaction profile all confirm that rapid stereo­specific 1,3‑CH bond addition across the Zr­(η²-alkene) bond of <b>A</b> follows the rate-determining β‑H abstraction reaction. DFT computations also suggest that an α‑CC agostic rotamer of [Cp₂Zr­(<i>c</i>-C₃H₅)₂] assists the β‑H abstraction of cyclo­propane. The nature of the α‑CC agostic interaction is discussed in the light of an NBO analysis

β‑H Abstraction/1,3‑CH Bond Addition as a Mechanism for the Activation of CH Bonds at Early Transition Metal Centers

This article describes the generalization of an overlooked mechanism for CH bond activation at early transition metal centers, namely 1,3‑CH bond addition at an η²-alkene intermediate. The X-ray-characterized [Cp₂Zr­(<i>c</i>-C₃H₅)₂] eliminates cyclo­propane by a β‑H abstraction reaction to generate the transient η²-cyclo­propene [Cp₂Zr­(η²-<i>c</i>-C₃H₄)] intermediate <b>A</b>. <b>A</b> rapidly cleaves the CH bond of furan and thiophene to give the furyl and thienyl complexes [Cp₂Zr­(<i>c</i>-C₃H₅)­(2-C₄H₃X)] (X = O, S), respectively. Benzene is less cleanly activated. Mechanistic investigations including kinetic studies, isotope labeling, and DFT computation of the reaction profile all confirm that rapid stereo­specific 1,3‑CH bond addition across the Zr­(η²-alkene) bond of <b>A</b> follows the rate-determining β‑H abstraction reaction. DFT computations also suggest that an α‑CC agostic rotamer of [Cp₂Zr­(<i>c</i>-C₃H₅)₂] assists the β‑H abstraction of cyclo­propane. The nature of the α‑CC agostic interaction is discussed in the light of an NBO analysis

Chemo‑, Regio‑, and Stereoselective Silver-Catalyzed Aziridination of Dienes: Scope, Mechanistic Studies, and Ring-Opening Reactions

Silver complexes bearing trispyrazolylborate ligands (Tp^x) catalyze the aziridination of 2,4-diene-1-ols in a chemo-, regio-, and stereoselective manner to give vinylaziridines in high yields by means of the metal-mediated transfer of NTs (Ts = <i>p</i>-toluensulfonyl) units from PhINTs. The preferential aziridination occurs at the double bond neighboring to the hydroxyl end in ca. 9:1 ratios that assessed a very high degree of regioselectivity. The reaction with the silver-based catalysts proceeds in a stereospecific manner, i.e., the initial configuration of the CC bond is maintained in the aziridine product (<i>cis</i> or <i>trans</i>). The degree of regioselectivity was explained with the aid of DFT studies, where the directing effect of the OH group of 2,4-diene-1-ols plays a key role. Effective strategies for ring-opening of the new aziridines, deprotection of the Ts group, and subsequent formation of β-amino alcohols have also been developed