Reactivity of a Gold-Aluminyl Complex with Carbon Dioxide: A Nucleophilic Gold?

Abstract

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-CO 2 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 CO 2 .

What Singles out Aluminyl Anions? A Comparative Computational Study of the Carbon Dioxide Insertion Reaction in Gold–Aluminyl, −Gallyl, and −Indyl Complexes

“…For CO 2 insertion into the Au–Al bond of the [ t Bu 3 PAuAl(NON)] complex I , 3 we found a two-step mechanism characterized (i) by a nucleophilic attack to the CO 2 carbon atom performed by the Au–Al bond also assisted by the electrophilic Al “empty” p orbital, followed (ii) by a rearrangement driven by an electrophilic attack to the oxygen atom of CO 2 by the aluminum center, leading to the formation of the insertion product where the CO 2 carbon atom is coordinated to gold and both the CO 2 oxygen atoms are coordinated to Al (complex II , see Scheme 1 ). 9 , 11 Transition states and intermediate structures pointed out a radical-like insertion of CO 2 in the Au–Al bond, which was consistently shown to have mainly an electron-sharing character. In the following, we applied the same systematic computational strategy used in ref ( 9 ), that is, density functional theory (DFT) with inclusion of scalar relativistic effects, solvation (toluene), and dispersion corrections (see the “ Computational Details ” section), for the study of CO 2 insertion into the Au–X bond in complexes I X (X = Al, Ga, and In).…”

“… 9 , 11 Transition states and intermediate structures pointed out a radical-like insertion of CO 2 in the Au–Al bond, which was consistently shown to have mainly an electron-sharing character. In the following, we applied the same systematic computational strategy used in ref ( 9 ), that is, density functional theory (DFT) with inclusion of scalar relativistic effects, solvation (toluene), and dispersion corrections (see the “ Computational Details ” section), for the study of CO 2 insertion into the Au–X bond in complexes I X (X = Al, Ga, and In). Analogous to [ t Bu 3 PAuAl(NON)], complexes I X have been slightly simplified at the Si NON site by replacing the two Dipp substituents on the nitrogen atoms with phenyl groups (denoted as Si NON′).…”

“…The free energy profiles for all systems are shown in Figure 1 . For the reader’s convenience we also include the reaction profile for the gold–aluminyl [ t Bu 3 PAuAl(NON′)] complex reported in ref ( 9 ). Optimized structures of reactants (RC), transition states (TSI, TSII), intermediates (INT), and products (PC) for [ t Bu 3 PAuAl(NON′)] and [ t Bu 3 PAuX( Si NON′)] (X = Al, Ga, and In) complexes are sketched with selected geometrical parameters in Figure 2 , whereas fully optimized geometries for all the species involved in the whole path are reported in Figures S1–S4 .…”

“…We showed that the Au–Al bond is of the electron-sharing type, with Au and Al cooperatively inserting CO 2 with a radical-like reactivity. 9 …”

Coinage metal aluminyl complexes: probing regiochemistry and mechanism in the insertion and reduction of carbon dioxide

“…The addition of one molecule of CO 2 to 3-Ag takes place with very low activation energies via the intermediate IM1-Ag, giving the dioxocarbene complex 4-Ag as the rst product. The calculations suggest that CO 2 uptake starts with side-on [2 + 2] addition of one C]O bond to the Al-Ag bond (with a regiochemistry reecting polarization in the sense Ag(dÀ)-Al(d+)), 25,35,43 and that the intermediate IM1-Ag then rearranges via TS2-Ag to give dioxocarbene complex 4-Ag. From this species, the second part of the reaction sequence 4-Ag / 6-Ag proceeds via initial CO extrusion, yielding 8-Ag as an intermediate (featuring an Ag-O-Al unit), preceded by IM2-Ag as a weakly bonded silver-CO complex precursor.…”