Aluminium(I) nucleophiles

However, upon reducing of the metal center, aluminium(I) compounds may gain a lone pair which confers them nucleophilic character.

The first aluminyl anion to be isolated by Aldridge, Goicoechea and coworkers is supported by a xanthene-based diamido ligand, referred to as NON by the authors.

Following the two electron reduction, a bright-yellow dimeric species with the chemical formula K2[Al(NON)]2 was formed, as confirmed by X-ray crystallography.

The two monomeric units are joined by electrostatic interactions between the positively charged potassium cations and the electron clouds of the Dipp (diisopropylphenyl) substituents.

[10] Following this initial synthesis, other nucleophilic diamido aluminyl anions have been reported, also synthesized through the reduction of the corresponding aluminium(III) iodide with excess potassium graphite and also isolated as a dimeric species with a similar structure to that of K2[Al(NON)]2.

Following the second reduction step of the dialumane, the dialkyl aluminyl anion was isolated as a monomer stabilized through weak electrostatic interactions with the potassium based cation.

[4] In all cases, the highest occupied molecular orbital (HOMO) of aluminyl anions is the aluminium lone pair which confers these compounds nucleophilic character.

In addition, the aluminyl anions have been shown to undergo cycloaddition reactions with alkenes, alkynes, and polyaromatics, similar to singlet carbenes, which can be attributed to the ambiphilic character of the aluminium(I) center.

[5][16] Similarly, Hill and McMullin's dimeric diamido aluminyl anion can react with magnesium or calcium electrophiles to form new metal-metal bonds.

Aldridge and Goicoechea's first synthesis of a nucleophilic aluminyl anion. [ 5 ]
Syntheses of alkyl aluminyl anions via the reduction of dialumane intermediates: a.Yamashita's synthesis of a dialkyl aluminyl anion; [ 13 ] and b. Kinjo's synthesis of an alkyl-amido aluminyl anion. [ 14 ]
Contour plot of electron density Laplacian values in the plane of the heterocycle for a model NacNac-supported aluminium(I) molecule, depicting electron density accumulation and the nucleophilic aluminium(I) lone pair. Plot adapted from the work of Cimpoesu and coworkers. [ 15 ]
Nucleophilicty of aluminyl anions in nucleophilic substitution reactions: a. selected reactivity of Aldridge and Goicoechea's diamido aluminyl anion; [ 5 ] [ 16 ] b. selected reactivity of Hill and McMullin's diamido aluminyl anion; [ 12 ] and c. selected reactivity of Yamashita's dialkyl aluminyl anion. [ 13 ] [ 17 ]