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 [N 2 ], [CO] and [Ph(H)C] units driven thermodynamically by Al-O bond formation. N 2 O reacts rapidly to generate the organoazide DippN 3 (Dipp=2,6- i Pr 2 C 6 H 3 ), while CO 2 (under dilute reaction conditions) yields the corresponding isocyanate, DippNCO. Mechanistic studies, using both experimental and quantum chemical techniques, identify a carbamate complex K 2 [(NON)Al-{κ 2 -(N,O)-N(Dipp)CO 2 }] 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 K 2 [(NON)Al{κ 2 -(O,O')-(O 2 C) 2 N-(Dipp)}] (via the take-up of a second equivalent of CO 2 ). In the case of benzaldehyde, a similar [2+2] cycloaddition process generates the metallacyclic hemi-aminal complex, K n [(NON)Al{κ 2 -(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, K 2 [(NON)Al(O)] 2 . However, addition of CO 2 allows the imine to be released, driven by the formation of the thermodynamically more stable aluminium carbonate co-product, K 2 [(NON)Al(κ 2 -(O,O')-CO 3 )] 2 .