σ-Cyclopropyl to π-Allyl Rearrangement at AuIII.

The possibility for AuIII σ-cyclopropyl complexes to undergo ring-opening and give π-allyl complexes was interrogated. The transformation was first evidenced within (P,C)-cyclometalated complexes, it occurs within hours at -50 °C. It was then generalized to other ancillary ligands. With (N,C)-cyclometalated complexes, the rearrangement occurs at room temperature while it proceeds already at -80 °C with a dicationic (P,N)-chelated complex. Density Functional Theory (DFT) calculations shed light on the mechanism of the transformation, a disrotatory electrocyclic ring-opening. Intrinsic Bond Orbital (IBO) analysis along the reaction profile shows the cleavage of the distal σ(CC) bond to give a π-bonded allyl moiety. Careful inspection of the structure and bonding of cationic σ-cyclopropyl complexes support the possible existence of C-C agostic interactions at AuIII .

Energetics of key Au(III)-substrate adducts relevant to catalytic hydroarylation of alkynes.

(P,C)-cyclometalated Au(III) complexes have shown remarkable ability to catalyze the intermolecular hydroarylation of alkynes. Evidence of an outer-sphere mechanism has been provided in a previous study and is confirmed here by analysing the experimental data and DFT calculations. In this work, we propose evaluation of critical energies of dissociation of Au(III) complexes with different substrates via energy-resolved mass spectrometry (ERMS) experiments and kinetic modelling. The kinetic model is based on a multi-collisional approach. On the one hand, the classification confirms the mechanism previously proposed; on the other hand, it supports the collisional model and its application to particularly fragile adducts.