An Aluminium Imide as a Transfer Agent for the [NR]²⁻ Function via Metathesis Chemistry

The reactions of a terminal aluminium imide with a range of oxygen-containing substrates have been probed with a view to developing its use as a novel main group transfer agent for the [NR]²⁻ fragment. We demonstrate transfer of the imide moiety to [N₂], [CO] and [Ph(H)C] units driven thermodynamically by Al−O bond formation. N₂O reacts rapidly to generate the organoazide DippN₃ (Dipp=2,6-ⁱPr₂C₆H₃), while CO₂ (under dilute reaction conditions) yields the corresponding isocyanate, DippNCO. Mechanistic studies, using both experimental and quantum chemical techniques, identify a carbamate complex K₂[(NON)Al-{κ²−(N,O)−N(Dipp)CO₂}]₂ (formed via [2+2] cycloaddition) as an intermediate in the formation of DippNCO, and also in an alternative reaction leading to the generation of the amino−dicarboxylate complex K₂[(NON)Al{κ²−(O,O′)−(O₂C)₂N-(Dipp)}] (via the take-up of a second equivalent of CO₂). In the case of benzaldehyde, a similar [2+2] cycloaddition process generates the metallacyclic hemi-aminal complex, K_n[(NON)Al{κ²−(N,O)−(N(Dipp)C(Ph)(H)O}]_n. Extrusion of the imine, PhC(H)NDipp, via cyclo-reversion is disfavoured thermally, due to the high energy of the putative aluminium oxide co-product, K₂[(NON)Al(O)]₂. However, addition of CO₂ allows the imine to be released, driven by the formation of the thermodynamically more stable aluminium carbonate co-product, K₂[(NON)Al(κ²−(O,O′)−CO₃)]₂.