Search

International audience; The role of Hartree-Fock exchange in describing the structural changes occurring upon reduction of bipyridine-based ligands and their complexes is investigated within the framework of density functional theory calculations. A set of 4 free ligands in their neutral and radical anionic forms, and 2 of their zinc complexes in their dicationic and monocationic radical forms, is used to compare a large panel of pure, conventional, and long-range corrected hybrid DFT functionals; coupled cluster single and double calculations are used alongside experimental results as benchmarks. Particular attention has been devoted to the magnitude of the change, upon reduction, of the D-parameter, which measures the difference between the Cpy-Cpy and the C-N bond lengths in bipyridine ligand and is known to experimentally correlate with the charge of the ligands. Our results indicate that the structural changes significantly depend on the amount of exact exchange included in the functional. A progressive evolution is observed for the free ligands, whereas two distinct sets of results are obtained for the complexes. Functionals with a small degree of HF exchange, e.g., B3LYP, do not adequately describe geometric changes for the considered species and, quite surprisingly, the same holds for the CC2 method. The best agreement to experimental and CCSD values is obtained with functionals that include a significant but not excessive part of exact exchange, e.g., CAM-B3LYP, M06-2X, and wB97X-D. The calculated localisation of the added electron after reduction, which depends on the self-interaction error, is used to rationalize these outcomes. Static correlation is also shown to play a role in the accurate description of electronic structure.

A density functional theory (DFT) investigation performed at the B3LYP/TZVP//B3LYP/6-31G(d)-LANL2DZ level of theory on the hydroamination of dimethylamine (Me2NH) on an activated olefin (namely, acrylonitrile (CH2═CHCN)), as catalyzed by a 1,2,4-triazol based nickel(II) N-heterocyclic carbene complex (namely, [1,4-dimethyl-1,2,4-triazole-5-ylidene]2 nickel dichloride) revealed that the olefin coordination pathway is favorable over the amine coordination pathway, although the initial olefin coordination step is higher in energy than the initial amine coordination step. Significantly enough, the reaction involved a crucial 1,3-proton transfer step between the resonance intermediates, i.e., the C-bound [(NHC)2Ni(CH(CN)CH2NHMe2)]+ (D) species or N-bound [(NHC)2Ni(NCCHCH2NHMe2)]+ (E) species and the intermediate [(NHC)2Ni(NCCH2CH2NMe2)]+ (F), depicting the cleavage of a N–H bond and the formation of a C–H bond facilitated by a water-assisted/amine-assisted proton shuttle. Overall, among the various pathways ex...

International audience; This work aims to improve the computation of infrared spectra of gas-phase cations using DFT methods. Experimental IRMPD spectra for ten Zn and Ru organometallic complexes have been used to provide reference data for 64 vibrational modes in the 900-2000 cm-1 range. The accuracy of the IR vibrational frequencies predicted for these bands has been assessed over five DFT functionals and three basis sets. The functionals include the popular B3LYP and M06-2X hydrids and the range-separated hybrids (RSH) CAM-B3LYP, LC-BLYP and B97X-D. B3LYP gives the best mean absolute error (MAE) and root-mean-square error (RMSE) values of 7.1 and 9.6 cm-1 , whilst the best RSH functional, B97X-D, gives 12.8 and 16.6 cm-1 respectively. Using linear correlations instead of scaling factors improves the prediction accuracy significantly for all functionals. Experimental and computed spectra for a single complex can show significant differences even when the molecular structure is calculated correctly, and a means of defining confidence limits for any given computed structure is also provided.

International audience; Combining electron capture dissociation mass spectrometry and infrared multiple photon dissociation action spectroscopy allows the formation, selection and characterisation of reduced metal complexes containing non-innocent ligands. Zinc complexes containing diazafluorenone ligands have been studied and the localisation of the single electron on the metal atom in the mono-ligated complex has been demonstrated.

The lability of a trans "throwaway" pyridine ligand in a PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) themed saturated six-membered N-heterocyclic carbene complex namely, (1,3-difurfuryl tetrahydropyrimidin-2-ylidene)PdCl2(pyridine) (2), was investigated with the aid of a combined experimental and computational studies. In this regard, a new saturated six-membered N-heterocyclic carbene complex 2 was synthesized from the reaction of 1,3-difurfuryl tetrahydropyrimidin-1-ium chloride (I) with PdCl2 in the presence of KN(SiMe3)(2) as a base in pyridine. Significantly enough, the complex 2 represents the first structurally characterized example of a PEPPSI themed trans-(NHC)PdX2(pyridine) (X = halide) type of a complex supported over a saturated six-membered N-heterocyclic carbene ligand. The lability of a trans "throwaway" pyridine ligand in 2 was probed by a displacement reaction with PPh3 to yield the corresponding phosphine analog, (1,3-difurfuryl tetrahydropyrimidin-2-ylidene)PdCl2(PPh3) (3), at room temperature under ambient condition. Detailed density functional theory (DFT) studies aimed at understanding the lability of the trans "throwaway" pyridine ligand in 2, against a PPh3 ligand yielding 3, points towards a kinetic factor rather than a thermodynamic one as a reason for the lability of the pyridine in 2. (C) 2012 Elsevier Ltd. All rights reserved.

A gold(I) N-heterocyclic carbene (NHC) complex mediated hydroamination of an alkyne has been modeled using density functional theory (DFT) study. In this regard, alkyne and amine coordination pathways have been investigated for the hydroamination reaction between two representative substrates, namely, MeC≡CH and PhNH(2), catalyzed by a gold(I) NHC based (NHC)AuCl-type precatalyst, namely, [1,3-dimethylimidazol-2-ylidene]gold chloride. The amine coordination pathway displayed a lower activation barrier than the alkyne coordination pathway. The catalytic cycle is proposed to proceed via a crucial proton-transfer step occurring between the intermediates [(NHC)AuCH═CMeNH(2)Ph](+) (D) and [(NHC)Au(PhNHMeC═CH(2))](+) (E), the activation barrier of which was found to be significantly reduced by a proton relay mechanism process assisted by the presence of any adventitious H(2)O molecule or even by any of the reacting PhNH(2) substrates. The final hydroaminated enamine product, PhNHMeC═CH(2), was further seen to be stabilized in its tautomeric imine form PhN═CMe(2).