Abstract
The synthesis and isolation of novel low oxidation state aluminium (Al) compounds has seen relatively slow progress over the 30 years since such species were first isolated. This is largely due to the significant challenges in isolating these thermodynamically unstable compounds. Despite challenges with isolation, their reactivity has been widely explored and they have been utilized in a wide range of processes including the activation of strong chemicals bonds, as ligands to transition metals and in the formation of heterobimetallic M–M compounds. As such, attempts to isolate novel low oxidation state Al compounds have continued in earnest and in the last few years huge advances have been made. In this review we highlight the remarkable recent developments in the low oxidation state chemistry of aluminium and discuss the variety of new reactions these compounds have made possible.
Highlights
The last few years have seen an explosion in this eld, with the isolation and characterisation of a range of complexes that offer exciting new reactivity. We focus on these monumental advances that have set the stage for the future of main-group chemistry with commentary on the development of [1] aluminium–aluminium multiple bonds; [2] nucleophilic aluminium(I) alumanyl anions; [3] new monomeric aluminium(I) species and [4] the isolation of aluminium(I) hydrides
Over just the last four years a wealth of new research into the low oxidation state chemistry of aluminium has emerged. This has largely been possible through the rational design of complexes, with judicious choice of the ancillary ligands which are essential to enabling stabilisation of these highly reactive compounds
Aldridge and Goicoechea's potassium alumanyl species has shown utility in a wide range of bond activation processes and has been used to provide access to unusual chemical structures such as the seven membered metallocycle formed through the C–C bond activation of benzene
Summary
Recent years have seen a renaissance in main-group chemistry, with novel main-group compounds being shown to adopt unusual electronic con gurations, demonstrate application in the activation of strong chemical bonds and facilitate a wide range of catalytic processes.1–3 In particular, the potential for main-group elements to adopt reactivity more commonly associated with transition metals is being widely explored, with redox type processes becoming less chemical curiosities and more valuable synthetic methodologies.4–7 AluminiumThe use of aluminium in major industrial catalytic processes dates back to the late 19th century, when aluminium(III) chloride was used to mediate the Friedel–Cra s reaction.10 In the 1950s Ziegler demonstrated the use of aluminium hydrides in the Au au (chain growth) reaction of ethylene, a process that revolutionised modern manufacturing.11 In the ensuing years, aluminium's catalytic capabilities has been demonstrated in both hetero- and homogeneous systems for a range ofKatie Hobson received her MSci in Chemistry from University College London in 2018 where her 4th year project focused on the development of n-type transparent conducting oxides under the supervision of Professor Claire Carmalt. Following on from the seminal isolation of NON–Al complexes, Coles and co-workers expanded this work by investigating the reactivity of a novel alumanyl anion with 1,3,5,7cyclooctatetraene (COT).45 In an analogous fashion, the aluminium iodide [31] was reduced with potassium metal to form the alumanyl anion, 32, which exists as dimer containing two anionic [Al(NONAr)]À units (Fig. 10).
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