Bond-Dissociation Energies to Probe Pyridine Electronic Effects on Organogold(III) Complexes: From Methodological Developments to Application in π-Backdonation Investigation and Catalysis

In this work, we report on the synthesis of several organogold(III)complexes based on 4,4 & PRIME;-diterbutylbiphenyl (C<^>C) and 2,6-bis(4-terbutylphenyl)pyridine(C<^>N<^>C) ligands and bond with variously substituted pyridine ligands(pyrR). Altogether, 33 complexes have been prepared and studied withmass spectrometry using higher-energy collision dissociation (HCD)in an Orbitrap mass spectrometer. A complete methodology includingthe kinetic modeling of the dissociation process based on the Rice-Ramsperger-Kassel-Marcus(RRKM) statistical method is proposed to obtain critical energies E (0) of the pyrR loss for all complexes. The capacityof these E (0) values to describe the pyridineligand effect is further explored, at the same time as more classicaldescriptors such as H-1 pyridinic NMR shift variation uponcoordination and Au-N-pyrR bond length measured byX-ray diffraction. An extensive theoretical work, including densityfunctional theory (DFT) and domain-based local pair natural orbitalcoupled-cluster theory (DLPNO-CCSD(T)) methods, is also carried outto provide bond-dissociation energies, which are compared to experimentalresults. Results show that dissociation energy outperforms other descriptors,in particular to describe ligand effects over a large electronic effectrange as seen by confronting the results to the pyrR pK (a) values. Further insights into the Au-N-pyrR bond are obtained through an energy decomposition analysis (EDA)study, which confirms the isolobal character of Au+ withH(+). Finally, the correlation between the lability of thepyridine ligands toward the catalytic efficiency of the complexescould be demonstrated in an intramolecular hydroarylation reactionof alkyne. The results were rationalized considering both pre-catalystactivation and catalyst reactivity. This study establishes the possibilityof correlating dissociation energy, which is a gas-phase descriptor,with condensed-phase parameters such as catalysis efficiency. It thereforeholds great potential for inorganic and organometallic chemistry byopening a convenient and easy way to evaluate the electronic influenceof a ligand toward a metallic center. Acomplete mass spectrometry-based methodology is developedto determine accurate metal-ligand bond-dissociation energiesof 33 organogold(III) complexes. These energies are able to providea reliable evaluation of the ligand influence over a large range ofelectronic effects and also help in rationalizing the catalytic activityof the complexes.