Structure and reactivity of an Al/P-based frustrated Lewis pair bearing relatively small substituents at aluminium.

Reaction of Mes2P─C≡C─Ph (Mes = mesityl) with dineopentylaluminium hydride afforded by hydroalumination a geminal Al/P-based frustrated Lewis pair (FLP; 4). Its steric shielding is relatively low, and its reactivity in various secondary reactions is less hindered by steric repulsion than observed for related compounds having bulkier groups attached to aluminium. FLP 4 yielded adducts with Me3C─NCO or benzaldehyde via the formation of Al-O and P-C bonds. Trimethylsilyl azide reacted with 4 under surprisingly mild conditions to afford a nitrene complex by spontaneous N2 elimination below room temperature. A carbodiimide molecule was coordinated via one of the C=N bonds to form a five-membered AlCPNC heterocycle with an intact C=N bond in an exocyclic position. A very large molecule was obtained by the reaction of two equivalents of 4 with a bifunctional methylene-bridged phenylene isocyanate precursor.This article is part of the themed issue 'Frustrated Lewis pair chemistry'.