Gold-Aluminyl and Gold-Diarylboryl Complexes: Bonding and Reactivity with Carbon Dioxide

The unconventional carbon dioxide insertionreaction of a gold-aluminyl [tBu3PAuAl(NON)] complex hasbeen recently shown to be related to the electron-sharing characterof the Au-Al bond that acts as a nucleophile and stabilizes theinsertion product through a radical-like behavior. Since a gold-diarylboryl [IPrAuB(o-tol)2] complex with similar reactivityfeatures has been recently reported, in this work we computation-ally investigate the reaction of carbon dioxide with [LAuX] (L =phosphine, N-heterocyclic carbene (NHC); X = Al(NON), B(o-tol)2) complexes to get insights into the Al/B anionic and goldancillary ligand effects on the Au-Al/B bond nature, electronicstructure, and reactivity of these compounds. We demonstrate thatthe Au-Al and Au-B bonds possess a similar electron-sharing nature, with diarylboryl complexes displaying a slightly morepolarized bond as Au(delta+)-B(delta-). This feature reduces the radical-like reactivity toward CO2, and the Al/B anionic ligand effect isfound to favor aluminyls over boryls, despite the greater oxophilicity of B. Remarkably, the ancillary ligand of gold has a negligibleelectronic trans effect on the Au-X bond and only a minor impact on the formation of the insertion product, which is slightly morestable with carbene ligands. Surprisingly, wefind that the modification of the steric hindrance at the carbene site may exert a sizablecontrol over the reaction, with more sterically hindered ligands thermodynamically disfavoring the formation of the CO2insertionproduct.

Automated summary

The study investigates the properties and influencing factors of the reactions between gold-aluminyl and gold-boryl complexes with CO2. The results show that the gold-aluminyl and gold-boryl bonds have similar electron-sharing properties, with the gold-boryl bond being slightly more polarized, resulting in lower radical reactivity. Under the influence of ligands, aluminyl products are favored over boryl products, and the gold ancillary ligand has minimal impact on the formation and stability of the reaction products, while carbene ligands are slightly better than phosphine ligands. Furthermore, the steric hindrance at the carbene ligand site plays an important role in the formation of the reaction product.