Aluminyl Anions

Abstract

In 2018, a new class of low‐valent aluminum compound was introduced to the chemical literature. Aluminyl anions [Al (I) (L 2 )] − consist of an Al(I) center supported by a range of (predominantly chelating) dianionic ligand scaffolds, [L 2 ] 2− . The resulting negative charge is balanced by a group 1 metal cation with examples spanning all of the stable alkali metals Li, Na, K, Rb, and Cs. The nature and extent of cation···anion interactions can be controlled, affording three distinct structural types classified as a contacted dimeric pair (CDP), a monomeric ion pair (MIP), or a separated ion pair (SIP). The chemistry of these systems has proven to be very diverse, primarily driven by the oxidation of the aluminum to a more stable Al(III) center. Researchers have been able to harness this thermodynamically favored process to promote a number of different reactions. This article describes the oxidative addition reactions of X–Y sigma bonds to aluminyl anions, to form the corresponding aluminate products [Al (III) (L 2 )(X)(Y)] − , containing examples of new (AlH, AlB, AlC, AlN, AlO, AlF, AlSi, and AlP) bonds. The oxidation of aluminyl anions has been expanded to access compounds with new aluminum–element multiple bonds including examples of AlCR 2 ‐, AlO‐, AlS‐, AlSe‐, AlTe‐, and AlNR‐containing compounds. These terminal bonds react via [2+2] cycloaddition with unsaturated substrates to form new products, demonstrating a preference to react through formally double AlX bonds. Finally, a brief description of the application of aluminyl anions for the reductive coupling of small molecules is included. Examples involving the homocoupling of P 4 ; the homologation of CO; and the dimerization of ketones, isocyanides, and diazomethane are provided. Under favorable conditions, these couplings have been recently extended to include examples of heterocoupling of substrates, demonstrating a high degree of control of product formation.