RESUMEN
A library of novel structurally related singlet carbenes, namely, acyclic amino(haloaryl)carbenes, was designed by a high-yielding two-step procedure, and their chemical stability explored both experimentally and theoretically. Thanks to a careful selection of both the amino and the aryl substitution pattern, these carbenes exhibit a wide range of stability and reactivity, spanning from rapid self-dimerization for carbenes featuring ortho-F substituents to very high chemical stability as bare carbenes, up to 60 °C for several hours for compounds carrying ortho-Br substituents. Their structure was determined through NMR and X-ray diffraction studies, and their reactivity evaluated in benchmark reactions, highlighting the ambiphilic character of this novel class of singlet carbenes. In contrast with previously reported aryl substituents incorporating o-CF3 and t-Bu groups, which were considered "spectator", the high chemical stability of some of these carbenes relates to the stabilization of the σ-orbital of the carbene center by the π-accepting haloaryl substituent through delocalization. Kinetic protection of the carbene center is also provided by the ortho-halogen atoms, as demonstrated computationally. This push-pull stabilization effect makes acyclic amino(haloaryl) carbenes among the most ambiphilic stable carbenes reported to date, holding promise for a variety of applications.
RESUMEN
Herein is described a fully regio- and stereoselective hydroelementation reaction of SF5 -alkynes with N, O and S-nucleophiles and further functionalization of the corresponding Z-(hetero)vinyl-SF5 intermediates, a suitable platform to access α-SF5 ketones and esters, ß-SF5 amines and alcohols under mild reaction conditions. Experimental and computational comparative studies between SF5 - and CF3 -alkynes have been performed to highlight and explain the difference of reactivity and selectivity observed between these two fluorinated motifs.
RESUMEN
The presence of a cyclopropenimine moiety as the Lewis base partner in geminal frustrated Lewis pairs greatly enhances the reactivity of the system towards the activation of small molecules. This is mainly due to an increase of the aromaticity strength of this fragment during the activation reaction which results in a significant gain of stability ultimately leading to low barrier and high exergonic transformations.
RESUMEN
The influence of the replacement of CH groups by boron atoms on the reactivity of planar polycyclic aromatic hydrocarbons has been explored by means of computational tools. To this end, [4 + 2]-cycloaddition reactions involving anthracene and neutral boranthrene with different dienophiles such as ethylene, acetylene, and CO2 have been compared. In addition, the influence of additional fused aromatic rings (pentacene or borapentacene) on the reactivity of these species has been also explored. It was found that the B-doped systems are systematically much more reactive than their all-carbon counterparts from both kinetic and thermodynamic points of view. The observed trends in reactivity are quantitatively analyzed in detail using state-of-the-art methods, namely, the activation strain model of reactivity and the energy decomposition analysis method. Our calculations reveal the importance of molecular orbital interactions as the key factor responsible for the enhanced reactivity of the B-doped systems.
RESUMEN
The physical factors behind the experimentally observed high activity of gold(I)-catalysts having an α-cationic phosphole as a ligand have been computationally explored. To this end, the gold(I)-catalysed hydroarylation reactions of phenylacetylene and mesitylene involving both neutral and cationic phosphole as well as phosphine ligands have been quantitatively analyzed in detail with the help of the activation strain model of reactivity in combination with the energy decomposition analysis method. It is found that the cationic phosphole ligands induce a dramatic change in both the geometry and the electronic structure of the initially formed π-complex which significantly enhances its electrophilicity. This results in an enhancement of the key π(mesitylene) â π*(LAu-acetylene complex) molecular orbital interaction which is the main factor responsible for the activating effect of these cationic ligands.
RESUMEN
The so far poorly understood factors controlling the complete meta-selectivity observed in the C-H activation reactions of alkylarenes promoted by aluminyl anions have been explored in detail by means of Density Functional Theory calculations. To this end, a combination of state-of-the-art computational methods, namely the activation strain model of reactivity and energy decomposition analysis, has been applied to quantitatively unveil the origin of the selectivity of the transformation as well as the influence of the associated potassium cation. It is found that the selectivity takes place during the initial nucleophilic addition step where the key LP(Al)âπ*(C=C) molecular orbital interaction is more stabilizing for the meta-pathway, which results in a stronger interaction between the reactants along the entire transformation.
RESUMEN
The activation of a single C-F bond in di- and trifluoromethyl groups by frustrated Lewis pairs (FLPs) has been computationally explored by means of Density Functional Theory calculations. It is found that in this activation reaction the FLP partners exhibit a peculiar cooperative action, which is markedly different from related FLP-mediated processes, and where non-covalent interactions established between the Lewis base and the substrate play a decisive role. In addition, the process proceeds through the intermediacy of a hypervalent species featuring a pentacoordinate carbon atom, which is rare in the chemistry of FLPs. The physical factors controlling this process as well as the bonding situation of these hypervalent intermediates have been quantitatively analyzed in detail by using state-of-the-art computational methods to not only rationalize the mechanism of the transformation but also to guide experimentalists towards the realization of these so far elusive hypervalent systems.
RESUMEN
The factors controlling the oxidative addition of C-C and C-H bonds in arenes mediated by AlI have been computationally explored by means of Density Functional Theory calculations. To this end, we compared the processes involving benzene, naphthalene and anthracene which are promoted by a recently prepared anionic AlI -carbenoid. It is found that this species exhibits a strong tendency to oxidatively activate C-H bonds over C-C bonds, with the notable exception of benzene, where the C-C bond activation is feasible but only under kinetic control reaction conditions. State-of-the-art computational methods based on the combination of the Activation Strain Model of reactivity and the Energy Decomposition Analysis have been used to rationalize the competition between both bond activation reactions as well as to quantitatively analyze in detail the ultimate factors controlling these transformations.
RESUMEN
The role of frustrated Lewis pairs (FLPs) as ligands in gold(i) catalyzed-reactions has been computationally investigated by using state-of-the-art density functional theory calculations. To this end, the nature of (P,B)-FLP-transition metal interactions in different gold(i)-complexes has been first explored in detail with the help of the energy decomposition analysis method, which allowed us to accurately quantify the so far poorly understood AuB interactions present in these species. The impact of such interactions on the catalytic activity of gold(i)-complexes has been then evaluated by performing the Au(i)-catalyzed hydroarylation reaction of phenylacetylene with mesitylene. With the help of the activation strain model of reactivity, the factors governing the higher activity of Au(i)-complexes having a FLP as a ligand as compared to that of the parent PPh3 system have also been quantitatively identified.
RESUMEN
The influence of the nature of the group 14 elements (E = Si, Ge, Sn) on the reactivity of (F5C2)3E-CH2-P(tBu)2 geminal frustrated Lewis pairs (FLPs) has been computationally explored by means of density functional theory calculations. To this end, the experimentally described activation reactions of CO2 and phenyl isocyanate have been investigated and compared to the analogous processes involving the corresponding B/P geminal FLP. It is found that the reactivity of these species is kinetically enhanced when going down the group 14 (Si < Ge < Sn). This trend of reactivity is quantitatively analyzed in detail by means of the activation strain model of reactivity in combination with the energy decomposition analysis method, which identify the interaction energy between the deformed reactants as the main factor controlling the reactivity of these group 14 containing geminal FLPs.
RESUMEN
The role of carbones (CL2; L = phosphines vs carbenes) as Lewis bases in dihydrogen (H2) activation reactions in the presence of the Lewis acid B(C6F5)3 has been computationally explored by means of density functional theory calculations. To this end, the interaction between H2 and the [carbone···B(C6F5)3] pair along the reaction coordinate has been quantitatively analyzed in detail and compared to the parent [ tBu3P···B(C6F5)3] frustrated Lewis pair. In addition, the influence on the reactivity of both the nature of the central E atom and the surrounding ligands in ylidones (EL2) has also been considered. It is found that the activation barrier of the H2 activation reaction as well as the geometry of the corresponding transition states strongly depends on the nature of both E and L in the sense that lower barriers are systematically associated with earlier transition states. Our calculations identify heavier EL2 as the most active systems to achieve facile H2 activation reactions.
RESUMEN
The factors controlling the selectivity of the Diels-Alder cycloaddition reactions involving Fischer-type carbene complexes and cyclopentadiene have been explored computationally by means of density functional theory calculations. To this end, the influence of the substituents directly attached to the carbene ligand on the endo : exo ratio has been compared to the available experimental data and quantitatively analysed in detail by means of the combination of the activation strain model of reactivity and energy decomposition analysis methods. The insight gained in this computational study may be important for the rational design of exo-selective Diels-Alder reactions.
RESUMEN
Geminal frustrated Lewis pairs (FLPs) having a borole fragment as the Lewis acid partner constitute really promising candidates to achieve facile small molecule activation reactions. The predicted enhanced reactivity of these species, as compared to more traditional FLPs, finds its origin in the loss of the antiaromatic character of the borole moiety along the reaction coordinate.
RESUMEN
The influence of the nature of the acid/base pairs on the reactivity of geminal frustrated Lewis pairs (FLPs) (Me2 E-CH2 -E'Ph2 ) has been computationally explored within the density functional theory framework. To this end, the dihydrogen-activation reaction, one of the most representative processes in the chemistry of FLPs, has been selected. It is found that the activation barrier of this transformation as well as the geometry of the corresponding transition states strongly depend on the nature of the E/E' atoms (E=Groupâ 15 element, E'=Groupâ 13 element) in the sense that lower barriers are associated with earlier transition states. Our calculations identify the geminal N/Al FLP as the most active system for the activation of dihydrogen. Moreover, the barrier height can be further reduced by replacing the phenyl group attached to the acidic atom by C6 F5 or 3,5-(CF3 )2 C6 H3 (Fxyl) groups. The physical factors controlling the computed reactivity trends are quantitatively described in detail by means of the activation strain model of reactivity combined with the energy decomposition analysis method.
