Strong Electron-Donating Ligands Accelerate the Protodeauration Step in Gold(I)-Catalyzed Reactions: A Quantitative Understanding of the Ligand Effect

Abstract

We have conducted a theoretical exploration of the ligand electronic effect in the protodeauration step of a model gold(I) cyclization reaction, for which experimental data are available. The mechanism of the protodeauration is investigated through a density functional theory (DFT) approach, and the electron-donating power of the ligand is quantified through the charge displacement function (CDF). We find that the frequently encountered assumption in the literature that "strong electron-donating ligands accelerate the protodeauration" can be set into a quantitative framework by our combined DFT/CDF theoretical approach, which allows us also to rationalize the highest catalytic efficiency of Buchwald phosphine type ligands in this process. We analyze the ligand effect on the gold complex-substrate (LAu-S) bond strength, namely the bond to be broken during the protodeauration, and we find that the LAu-S interaction energies linearly correlate with the activation barriers. Finally, energy decomposition analysis (EDA) is used to investigate the LAu-S bond, and we show that changes in the interaction energies are mainly due to changes in the electrostatic component, whose value is in turn modulated by the ligand electron-donating power

Supported Au Nanoparticles with N-Heterocyclic Carbene Ligands as Active and Stable Heterogeneous Catalysts for Lactonization

“…13 Notably, Roth and Blum 22 observed that the presence of the NHC ligand nearly doubled the rate of proto-deauration compared to the analogous triphenylphosphine complex. In line with this experimental study, theoritical studies by Belanzoni and colleagues 23 showed that electron-donating ligands reduce the electrostatic component of the Au−C bond undergoing proto-deauration, which in turn reduces the activation barrier for this process. Given that NHCs are some of the most strongly electron-donating ancillary ligands, 24 the observed high activity of Cat-1 compared to Cat-0 is reasonable.…”

The role of the halogen bond in iodothyronine deiodinase: Dependence on chalcogen substitution in naphthyl‐based mimetics

“…The CD functions have been computed by carrying out single point energy calculations at the PB86/TZ2P level of theory on the B3LYP/6 – 31 + G(d,p) optimized geometries by employing ADF program package . Previous studies clearly showed that the CD function is marginally affected by the employed level of theory, so that we are confident that the present CD functions results at the PB86/TZ2P level are consistent with the B3LYP/6 – 31 + G(d,p) calculations. We also verified that the dispersion correction by Grimme (BP86‐D3) does not affect the charge density distribution.…”

“…An adequate choice is the isodensity boundary, where the electron density of the noninteracting fragments become equal. The CD analysis was successfully employed in the description of both coordination bonds and weak secondary interactions, such as HB and XB …”

Bond dissociation energies of carbonyl gold complexes: a new descriptor of ligand effects in gold(i) complexes?

“…The relative electron-donating abilities of the phosphine by inductive effect of the alkyl groups from Me to tBu stabilized the electrostatic interaction of the Au-CO bond, ∆Eelect, from -110.1 to -115.5 kcal/mol ( Table 2, entries 1-5). However, in contrast to the protodeauration step study by Belanzoni and co-workers, 39 the electrostatic contribution is quenched by the destabilizing Pauli repulsion term, going from 148.0 and 137.2 kcal/mol for 1-tBu and 5-Me respectively, and spanning an energy range of 10.8 kcal/mol. The positive value of the "ionic" contribution (∆E 0 = ∆Eelect + ∆EPauli) from 27.1 to 32.8 kcal/mol for 1-Me and 4-Cy and respectively) indicates that the interaction between the gold cationic moiety and CO is destabilized due to steric repulsion (ΔEPauli) and corresponds approximately to one half of the covalent component (∆Eoi ≈ -66 kcal/mol).…”