Controlled reductive C-C coupling of isocyanides promoted by an aluminyl anion.

We report the reaction of the potassium aluminyl, K[Al(NON)] ([NON] 2- = [O(SiMe 2 NDipp) 2 ] 2- , Dipp = 2,6-iPr 2 C 6 H 3 ) with a series of isocyanide substrates (R-NC). In the case of t Bu-NC, degradation of the isocyanide was observed generating an isomeric mixture of the corresponding aluminium cyanido-κ C and -κ N compounds, K[Al(NON)(H)(CN)]/K[Al(NON)(H)(NC)]. The reaction with 2,6-dimethylphenyl isocyanide (Dmp-NC), gave a C 3 -homologation product, which in addition to C-C bond formation showed dearomatisation of one of the aromatic substituents. In contrast, using adamantyl isocyanide Ad-NC allowed both the C 2 - and C 3 -homologation products to be isolated, allowing a degree of control to be exercised over the chain growth process. These data also show that the reaction proceeds through a stepwise addition, supported in this study by the synthesis of the mixed [(Ad-NC) 2 (Dmp-NC)] 2- product. Computational analysis of the bonding within the homologised products confirm a high degree of multiple bond character in the exocyclic ketenimine units of the C 2 - and C 3 -products. In addition, the mechanism of chain growth was investigated, identifying different possible pathways leading to the observed products, and highlighting the importance of the potassium cation in formation of the initial C 2 -chain.