Reactivity studies and structural outcomes of a bulky dialkylaluminium amide in the presence of the N-heterocyclic carbene, ItBu

• Published in: Polyhedron 2021-11, Vol.209, p.115469, Article 115469
• Main Authors: Pollard, Victoria A., Fuentes, Maria-Angeles, Robertson, Stuart D., Weetman, Catherine, Kennedy, Alan R., Brownlie, Josh, Angus, Fraser J., Smylie, Cooper, Mulvey, Robert E.
• Format: Article
• Language: English
• Subjects: Abnormal carbene; Alkali-metal; N-heterocyclic carbene; NMR studies; Organoaluminium compound
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2021.115469

Combining bulky molecules iBu2Al(TMP) and N-heterocyclic carbene, ItBu, affords an abnormal aItBu. Similar reactivity but with alkali metallation is observed in the co-presence of alkali-metal amides. Reactions with phenol and diphenylacetonitrile are straightforward producing complexes with the imidazolium cation [ItBu(H)]+. Bizarrely, the product of reaction of iBu2Al(TMP) (blue) and ItBu (red) with benzonitrile (green) is a complicated multicomponent assembly. [Display omitted] Aluminium reagent iBu2Al(TMP) (TMP is 2,2,6,6-tetramethylpiperidide) has previously shown interesting synergistic metallation chemistry when paired with alkali metal amides. Here its structural chemistry and reactivity is explored in the presence of the N-heterocyclic carbene, ItBu, 1,3-di-tert-butylimidazol-2-ylidene. Abnormal aItBu structures are obtained with iBu2Al(TMP) on its own and in the co-presence of LiTMP, NaTMP or KTMP. Reaction with phenol is stoichiometric dependent leading to the diphenolate [ItBu(H)]+ [(PhO)2Al(iBu)2]− and triphenolate [ItBu(H)]+ [(PhO)3Al(iBu)]− ionic complexes. Dinuclear aItBu(Ph)CN[Al(iBu)2NC(TMP)Ph]Al(iBu)2 was the surprising product from reaction with benzonitrile, displaying an imidoC- and (iBu)2Al- disubstituted imidazolium ring as well as a second imido unit made by addition of “non-nucleophilic” TMP across the benzonitrile triple bond. Potential insight into the mechanism of this intriguing complicated reaction was gained through the crystallographic characterisation of the ketamide [iBu2AlNC(Ph)TMP]2, a possible intermediate. Reaction with Ph2CHCN, diphenylacetonitrile, proved more straightforward affording the ionic complex [ItBu(H)]+ [Ph2CCN]−.