Paola Nava

Bonding of gold with unsaturated species.

Interactions of gold(I) catalysts with alkenes and alkynes are analyzed. Neutral chlorido, and cationic phosphine and N-heterocyclic carbene complexes are studied. High-level ab initio calculations are performed to benchmark the accuracy of popular DFT methods. Donation and backdonation contributions in the bond between the gold fragment and the alkene/alkyne substrate are discussed. These contributions depend on the nature of the gold fragment, but also on the substituents on the alkene/alkyne.

On the Catalysis of the Cycloisomerization of 1,6-Dienes with Tin(IV) Salts: The Important Role of a Water Molecule

A diene cycloisomerisation reaction catalysed by tin(IV) triflimidate is studied by using DFT computations. It is proposed that the mechanism does not involve the direct addition of the tin(IV) cation to a double bond because the catalyst regeneration step would be energetically unfeasible. We show that a water molecule may play a decisive role to enable the smooth completion of the catalytic cycle. The proposed active catalyst is thus a hydrated triflimidate salt. The hydrolysis and hydration energies are computed for three ligands of SnL4, L=triflate (OTf), triflimidate (NTf2) and a chlorosulfonate model (OSO2Cl). The diastereoselectivity observed in the cycloisomerisation is discussed in light of the transition‐state geometries. The hypothesis of hidden Brønsted acid catalysis is discussed and ruled out on the basis of new experimental results.

Labile ligands on some Lewis super acids: a computational study

Lewis super-acids, like Sn(OTf)(4) or In(OTf)(3), OTf = CF(3)SO(3)(-), are efficient catalysts for cycloisomerization reactions. We report here a study on the coordination of ligands (or of solvent molecules) around such catalysts at density functional theory level. Using the Sn-based compound as an example, we consider the interaction with several molecules, usually nearby in reaction conditions. These include nitromethane, esters and diesters, dimethylsulfoxide, and so on. We establish a ladder of interaction strengths and show that dimethylsulfoxyde molecules can displace triflate ligands from the metallic center. This leads to the main conclusions that solvent molecules directly coordinate Sn centers and that non-coordinating triflates are potentially free in solution despite their anionic characteristic.

Chemodivergent Palladium-Catalyzed Processes: Role of Versatile Ligands

Whereas the reaction of norbornadiene with terminal alkynes in the presence of a phosphapalladacycle catalyst leads to the formation of hydroalkynation products, the use of phosphinous acid–phosphinito‐containing palladium complexes gives rise to formal [2+1] cycloadducts. An experimental and computational approach was employed to study the mechanisms of the palladium‐promoted hydroalkynation and [2+1] cycloaddition. On the one hand, experiments highlight the crucial role of acidolysis steps on the catalytic activities. On the other hand, DFT calculations demonstrate the specificity of the phosphinito–phosphinous acid ligands, that is, the non‐equivalence of the two phosphorus atoms but the interchangeability of their properties. These results may have important implications for the mechanism of other palladium‐catalyzed transformations especially those involving phosphapalladacycles and phosphinous acid–phosphinito‐containing palladium complexes.