DFT study of chromium tricarbonyl complexes of coronene and kekulene

International audienceA quantum chemical study of the mechanism and determination of the activation barriers of intramolecular eta(6),eta(6)-inner-ring haptotropic rearrangements (IHR), consisting in moving a chromium tricarbonyl group Cr(CO)(3) from one six-membered aromatic ring to another, are carried out using the density functional theory (DFT) for the respective eta(6)-complexes of coronene I and kekulene II. The stationary states on the potential energy surface, determining the mechanism of eta(6),eta(6)-IHR, have a lower hapticity, which is of interest for catalysis because of the possibility of coordinating an additional substrate and reagent around the transition metal during the rearrangement. The processes of eta(6),eta(6)-IHR complexes I and II occur with similar energy barriers (Delta G(not equal) ae 20-25 kcal/mol) that are lower than the barriers (Delta G(not equal) ae 30 kcal/mol) of similar transformations previously calculated or measured for naphthalene complexes and a number of small polyaromatic hydrocarbons

1,6-Methano[10]annulene as prospective organometallic ligand from the annulene family A DFT study of transition metal π-complexes and their inter-ring haptotropic rearrangements

International audienceThe structural peculiarities (C1-C6 distances, bending of the ligand, conformation of organometallic group relative to the ligand, etc.), the isomerism and the mechanisms of inter-ring haptotropic rearrangements (IRHR) in Cr(CO)3 and CoCp complexes of 1,6-methano[10]annulene were investigated by DFT. An activation barrier of 28.0 kcal/mol, lower than that corresponding to naphthalene, was computed for the η6, η6-IRHR in the mononuclear chromium complex. In the case of the mononuclear cobalt species, activations barrier of 33.8 and 31.3 kcal/mol were computed for the η4, η4-IRHR in the trans and cis isomers, respectively

Thermally induced inter-ring haptotropic rearrangements in π-complexes of molybdenum with nitrogen containing polyaromatic heterocycles: A DFT study

International audienceInter-ring haptotropic rearrangements (IRHRs) are well-known phenomena in fluxional ogranometallic chemistry. They are mainly observed for transition metal complexes with polyaromatic ligands (PALs), but are usually limited to PALs without heteroatoms. Here, we report DFT studies of recent experimentally observed IRHRs in heterocyclic complexes of Mo. Four different ligands (quinoline, isoquinoline, quinoxaline, and indolyl) have been investigated. Overall, structural and energetic trends agree well with available experimental data. In addition, mechanistic trends and heteroatom participation are discussed and elucidated to further understanding of IRHRs in heterocyclic polyaromatic complexes in particular, and haptotropic processes in genera

Quantum chemical study of the structures and dynamic behavior of tricarbonyl complexes of Group 6 metals (Cr, Mo, W) with polyaromatic hydrocarbons using the density functional theory

International audienceThe quantum chemical study of the mechanism was performed for tricarbonyl eta(6)-complexes of coronene I-M and kekulene II-M (M = Cr, Mo, W) by the density functional method. The activation barriers of eta(6),eta(6)-interring haptotropic rearrangements (IHR), being the migration of the metaltricarbonyl group M(CO)(3) from one six-membered aromatic ring to another, were determined. The processes of eta(6),eta(6)-IHR in the metal tricarbonyl complexes with relatively high polycyclic aromatic hydrocarbons (PAH) I and II occur with close energy barriers (Delta G (not equal) ae 20-25 kcal mol(-1)), which are lower than the barriers (Delta G (not equal) similar to 30 kcal mol(-1)) of similar transformations measured or calculated earlier for the chromium tricarbonyl complexes of naphthalene and its derivatives and other PAH. For the molybdenum tricarbonyl complexes the activation barriers of eta(6),eta(6)-IHR decrease additionally by similar to 5 kcal mol(-1) compared to those for the chromium tricarbonyl complexes, whereas for the tungsten tricarbonyl complexes they increase again and become approximately equal to the activation barriers of similar chromium tricarbonyl complexes. All stationary states on the potential energy surface determining the mechanism of eta(6),eta(6)-IHR are characterized by a decrease in hapticity compared to the initial and final complexes

Influence of Ion Pairing in Inter-Ring Haptotropic Rearrangements in Cationic Cyclopentadienyl Complexes of Ruthenium with Naphthalene: A DFT Investigation

DFT calculations have been performed on the naphthalene cationic complex η⁶-C₁₀H₈RuCp⁺ in the presence of different anions. In a first step, geometry optimization of the PF₆^– salt carried out in the presence of 15 solvent molecules for 3 different solvents (methylene chloride, acetone, and water) indicated that ion pairing occurs in the less polar methylene chloride solvent, whereas the ions are separated in the more polar acetone and water. In a subsequent step, the inter-ring haptotropic rearrangement (IRHR) of η⁶-C₁₀H₈RuCp⁺ has been modeled both as an isolated cation (separated ion pairs (SIP)) and in the presence of a counterion (contact ion pair (CIP)). The IRHR activation barrier is found to be much lower in the CIP case due to the cation–anion interaction, which tends to reduce the metal unsaturation during the process. The size of the anion is also important. Small anions such as BF₄^– favor lower barriers. These results should also hold for photochemically induced IRHR processes, since the SIP mechanism involves structurally similar intermediates and transition states