Utilizing a sufficiently sterically demanding ligand, the terphenyl ligand AriPr8 (AriPr8 = C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2), allowed the isolation of the alanediyl :AlAriPr8 featuring a one-coordinate aluminum atom. The reactions of :AlAriPr8 with various organoazides RN3 afforded the tetrazole derivative AriPr8Al(NR)2N2 (R = 1-adamantyl), the amido-aluminum azide AriPr8Al(NR2)N3 (R = SiMe3), and the monomeric aluminum imide AriPr8AlNR (R = C6H3-2,6-(C6H2-2,4,6-Me3)2) which features an aluminum-nitrogen triple bond. Attractive London dispersion forces between the two terphenyl ligands in the triply bonded imide account for ca. 89 kJ/mol of the stabilization energy. Alternatively, treatment of AriPr8 with small molecules such as H2 and ethylene give products in which the substrates appear to add across an Al-Al bond. These findings suggest that monomeric :AlAriPr8 is in equilibrium with the dimeric dialuminene AriPr8AlAlAriPr8 in solution. Careful tuning of the organic substituents on the stabilizing terphenyl ligand may allow the isolation of the highly reactive species ArRAlAlArR.

Enforcing low coordination at aluminum using steric and dispersion force effects

ACS Spring 2022

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