Widening the Landscape of Small Molecule Activation with Gold‐Aluminyl Complexes: A Systematic Study of E−H (E=O, N) Bonds, SO₂ and N₂O Activation

Abstract

The electronic features of gold-aluminyl complexes have been thoroughly explored. Their similarity with Group 14 dimetallenes and other metal-aluminyl complexes suggests that their reactivity with small molecules beyond carbon dioxide could be accessed. In this work, the reactivity of the [ t Bu 3 PAuAl(NON)] (NON = 4,5-bis(2,6 diisopropylanilido)-2,7-ditert-butyl-9,9-dimethylxanthene) complex towards water, ammonia, sulfur dioxide and nitrous oxide is computationally explored. The reaction mechanisms computed for each substrate strongly suggest that all activation processes are in principle experimentally feasible. Electronic structure analysis highlights that, in all cases, the reactivity is driven by the presence of the poorly polarized electron-sharing goldaluminyl bond, which induces a radical-like reactivity of the complex towards all the substrates. A flat topology of the potential energy surface (PES) has been found for the reaction with N 2 O, where two almost isoenergetic transition states can be located along the same reaction coordinate with different geometries, suggesting that the N 2 O binding mode may not be a good indicator of the nature of N 2 O activation in a cooperative bimetallic reactivity. In addition, the catalytic potentialities of these complexes have been explored in the framework of nitrous oxide reduction. The study reveals that the [ t Bu 3 PAuAl(NON)] complex might be an efficient catalyst towards oxidation of phosphines (and boranes) via N 2 O reduction. These findings underline recurring trends in the novel chemistry of gold-aluminyl complexes and call for experimental feedbacks.

Coordination-induced O-H/N-H bond weakening by a redox non-innocent, aluminum-containing radical

“…However, though these results imply that e - transfer precedes H + transfer, the available data cannot elucidate the degree of coupled timing for e - transfer and H + transfer along the asynchronous PCET pathway. It is worth contrasting this behavior with a recently reported computational model 26 for X-H cleavage by a heterobinuclear Al-M complexes 24 with diradical character 25 . While facile X-H cleavage processes were observed in that system, they are proposed to involve a concerted, 2e - pathways and thus do not strictly qualify as PCET reactions enabled by CIBW.…”

“…Here, we demonstrate CIBW during O-H activation of water/alcohols and N-H activation of an amine at ambient conditions. Not only does this represent a rare example of CIBW by the most abundant metal on earth 24 – 26 , but also computational modeling suggests an unusual degree of CIBW. Most importantly, this discovery points to redox non-innocence 27 – 29 as a useful design element for enabling PCET with earth’s most abundant metals like aluminum and calcium.…”

Cooperative small molecule activation by apolar and weakly polar bonds through the lens of a suitable computational protocol

“…In a very recent computational work by us, we reported that analogous N 2 O activation with weakly polar, electron-sharing Au–Al bond in [ t Bu 3 PAuAl(NON)] complex may be feasible, resulting in the formation of the [ t Bu 3 PAuOAl(NON)] oxo-species (see 25 in Scheme 6) and N 2 extrusion. 63 This reaction has been predicted to be accessible from a kinetic point of view in mild conditions (Gibbs’ free energy activation barrier of 15.2 kcal mol −1 ). The reaction mechanism is qualitatively different from those illustrated so far for coinage metal–aluminyl reactions with CO 2 and H 2 .…”

“…We demonstrated that the [ t Bu 3 PAuAl(NON)] complex could, in principle, activate the N–H bond in ammonia in mild conditions, through a kinetically and thermodynamically favourable one-step process (Scheme 10). 63…”