A gold-aluminyl complex has been recently reported to feature an unconventional gold nucleophilic center, which was revealed through reactivity with carbon dioxide leading to the Au-CO2 coordination mode. In this work, we computationally investigate the reaction mechanism, which is found to be cooperative, with the gold-aluminum bond being the actual nucleophile and Al also behaving as electrophile. The Au-Al bond is shown to be mainly of an electron-sharing nature, with the two metal fragments displaying a diradical-like reactivity with CO2.