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Abstract: The hydrogenation reaction of multiple bonds that is mediated by geminal aminoborane‐based frustrated Lewis pairs (FLPs) has been explored by means of density functional theory calculations. It was found that the release of the activated dihydrogen occurred in a concerted, yet highly asynchronous, manner. The physical factors that control the transformation were quantitatively described in detail by using the activation strain model of reactivity in combination with the energy decomposition analysis method. This approach suggested a cooperative double hydrogen‐transfer mechanism, which involves the initial migration of the protic (N)H followed by the nucleophilic attack of the (B)H hydride to the carbon atom of the multiple bond. The influence of both the substituents directly attached to the boron atom of the initial FLP and the nature of the multiple bond on the transformation was also investigated. [ABSTRACT FROM AUTHOR]

H2 activation mediated by geminal aminoborane-based frustrated Lewis pairs (FLPs; R2N-CH2-BR′2) has been computationally explored within the density functional theory framework. It is found that the activation barrier of this process as well as the geometry of the corresponding transition states strongly depend on the nature of the substituents directly attached either to the acidic or the basic centers of the FLPs. The physical factors controlling the whole activation path are quantitatively described in detail by means of the activation strain model of reactivity combined with the energy decomposition analysis method. This methodology suggests a highly orbital-controlled mechanism where the degree of charge transfer cooperativity between the most important donor-acceptor orbital interactions, namely LP(N)→σ*(H2) and σ(H2)→pπ(B), along the reaction coordinate constitutes a suitable indicator of the reaction barrier. [ABSTRACT FROM AUTHOR]

DFT(M06-L) calculations have been used to determine the relativestabilities of the metallacyclobutane intermediates arising from thecross-metathesis reactions of terminal olefins as well as to get insightsinto the origin of the nondetection of the α,β-substitutedspecies. For that, we discuss the structures, NMR signatures, stabilitieswith respect to separated reactants, and experimentally proposed interconversionpathways of all potential metallacyclobutane intermediates arisingfrom propene and styrene homocoupling. For the case of propene, theunsubstituted and mono- and disubstituted metallacycles are lowerin Gibbs energy than the separated reactants under the NMR experimentalconditions. Moreover, for the same number of substituents, regardlessof their nature, the metallacycles presenting substituents at theCαcarbons are always lower in energy than thosepresenting substituents at Cβ, the energy differencebeing between 1.7 and 8.8 kcal mol–1. The computedenergy barriers associated with the olefin and carbene rotation processes,two of the experimentally proposed pathways for the metallacycle interconversion,are low and are in excellent agreement with the values previouslydetermined through NMR studies. Cycloaddition and cycloreversion energybarriers are also low, and in fact, there is not a significant differencebetween the barrier heights of the processes leading to observed ornonobserved intermediates. Therefore, the nondetection of metallacyclobutaneintermediates with substituents in Cβseems to arisefrom their lower stability in comparison with the isomers with substituentsin Cα, which makes their detection not feasible underthermodynamic equilibrium conditions. That is, for cross-metathesisprocesses involving small terminal alkenes and activated carbenes,the nature of the observed metallacycles is based on thermodynamiccontrol. The preference of having the substituents in Cαis attributed to the formation of stronger M–C and C–Cbonds during the cycloaddition when the substituents are in an αposition due to higher charge transfer from the original alkene fragmentto the metal carbene. [ABSTRACT FROM AUTHOR]

Photoelectronspectroscopy measurements and density functionalcalculations are combined to determine the lowest electron bindingenergies of first-row transition-metal aqua ions, titanium throughcopper, with 3d1through 3d9electronic configurations,in their most common oxidation states. Vertical ionization energiesare found to oscillate considerably between 6.76 and 9.65 eV for thedications and between 7.05 and 10.28 eV for the respective trivalentcations. The metal cations are modeled as [M(H2O)n]q牛겵 (q= 2, 3, and 4; n= 6 and 18) surroundedby continuum solvent. The performance of 10 exchange–correlationfunctionals, two GGAs, three MGGAs, two HGGAs and three HMGGAs, combinedwith the MDF10(ECP)/6-31(d,p) basis set is assessed for 11 M–Obond distances, 10 vertical ionization energies, 6 adiabatic ionizationenergies, and the associated reorganization free energies. We findthat for divalent cations the HGGA and HMGGA functionals in combinationwith the 18 water model show the best agreement with experimentalvertical ionization energies and geometries; for trivalent ions, theMGGA functionals perform best. The corresponding reorganization freeenergies (λo) of the oxidized ions are significantlyunderestimated with all DFT functionals and cluster models. This indicatesthat the structural reorganization of the solvation shell upon ionizationis not adequately accounted for by the simple solvation models used,emphasizing the importance of extended sampling of thermally accessiblesolvation structures for an accurate computation of this quantity.The photoelectron spectroscopy measurements reported herein providea comprehensive set of transition-metal redox energetic quantitiesfor future electronic structure benchmarks. [ABSTRACT FROM AUTHOR]