Probing the Extremes of Covalency in M−Al bonds: Lithium and Zinc Aluminyl Compounds

Abstract

Synthetic routes to lithium, magnesium, and zinc aluminyl complexes are reported, allowing for the first structural characterization of an unsupported lithium–aluminium bond. Crystallographic and quantum‐chemical studies are consistent with the presence of a highly polar Li−Al interaction, characterized by a low bond order and relatively little charge transfer from Al to Li. Comparison with magnesium and zinc aluminyl systems reveals changes to both the M−Al bond and the (NON)Al fragment (where NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene), consistent with a more covalent character, with the latter complex being shown to react with CO2 via a pathway that implies that the zinc centre acts as the nucleophilic partner.

Cooperative Activation of CO2 and Epoxide by a Heterobinuclear Al–Fe Complex via Radical Pair Mechanisms

“…Insertion of CO 2 into Al−M bonds with κ 2 binding to Al is rare, with previously reported examples involving low valent Al I rather than Al III precursors. 18,21,23,24 Compound 3 was stable to thermolysis and vacuum exposure, and we observed no evidence for conversion back to 2 under these conditions. In the 13 C{ 30 Complex 3 is stable thermally (up to 60 °C) in C 6 D 6 for at least 12 h but was found to react further upon irradiation with UV light.…”

“…18 In 2021, Roy et al reported CO 2 insertion into an Al−Zn bond (Figure 2c), although no mechanistic studies were reported. 24 Finally, in 2021, Escomel et al reported CO 2 deoxygenation by a Al III −Ir III complex that was proposed to go through a concerted transition state (Figure 2d). 9e We became interested in pursuing the chemistry of Al−Fe complexes, particularly those derived from Al III rather than Al I precursors.…”

Coordination and homologation of CO at Al(I): mechanism and chain growth, branching, isomerization and reduction

“…Complete details of synthetic methods and characterizing data, crystallographic information are details of quantum chemical studies are provided in the Supporting Information. Starting materials 57 and Ag2(squarate) 65 were prepared according to literature methods. All other reagents were used as received.…”

“…With this in mind, we targeted the reactivity of CO with related aluminyl compounds known to possess a mononuclear structure. The reaction of the (monomeric) lithium aluminyl complex (Et2O)2LiAl(NON) ([1-Li(OEt2)2]) 57 with CO was therefore probed under similar conditions. Intriguingly, this chemistry leads to the formation of a very similar dinuclear product, [2-Li(OEt2)]2, featuring an analogous [C4O4] 4fragment, and two encapsulated Li + counter-ions each ligated by two of the oxygen atoms of the [C4O4] 4unit and an additional molecule of diethyl ether.…”

Synthesis and Modular Reactivity of Low Valent Al/Zn Heterobimetallics Supported by Common Monodentate Amides

“…Their reactivity with unsaturated organic molecules (e. g. CO 2 , carbodiimides and recently [6c] also oxiranes) revealed mostly high regioselectivity upon insertion into an Al−M bond (Scheme 1: top) [2] . Focusing on the synthesis of Al−Zn bimetallics, seminal recent work by Goicoechea and Aldridge has revealed that the highly nucleophilic potassium aluminyl [(NON)AlK] 2 [NON=4,5‐bis(2,6‐diisopropylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene] supported by a xanthene‐based diamido ligand can undergo metathesis with [ Mes NacNacZnI] to form the zinc‐alumanyl ( I ) [6d] . Coles has reported closely related [( Si NON)AlZn Mes Nacnac] ( Si NON=O(SiMe 2 NDipp) 2 ] 2− ) ( II ) which is also accessible via metathesis [5g] .…”