Aluminium amides derived from metallation of N,N′-di-tert-butylethylenediamine

Abstract

The metallation of N,N′-di-tert-butylethylenediamine by AlH₃·NMe₃ has been investigated and shown to proceed via the formation of the unstable secondary amine-stabilised amidoalane [AlH₂(Bu^tNCH₂CH₂NBu^tH)]. This compound reacted with an additional equivalent of AlH₃·NMe₃ to yield the dibridging amidoalane complex [(AlH₂)₂{µ-N(Bu^t)CH₂CH₂N(Bu^t)}] or a molecule of the diamine to give the triamidoaluminium species [Al(Bu^tNCH₂CH₂NBu^t)(Bu^tNCH₂CH₂NBu^tH)]. In the absence of an excess of AlH₃·NMe₃ or N,N′-di-tert-butylethylenediamine, [AlH₂(Bu^tNCH₂CH₂NBu^tH)] eliminates molecular hydrogen to give the trans isomer of the dimeric diamidoalane complex trans-[{AlH[µ-N(Bu^t)CH₂CH₂NBu^t]}₂] which is stable toward reaction with either of the reactants. A stable analogue of the intermediate [AlH₂(Bu^tNCH₂CH₂NBu^tH)] was made by replacing a hydride by a chloride, achieved by using AlH₂Cl·NMe₃ as the metallating agent. The cis isomer of the dimeric diamidoalane cis-[AlH{[µ-N(Bu^t)CH₂CH₂NBu^t]}₂] was prepared from the unstable lithium diamido aluminium hydride species [{Li[N(Bu^t)CH₂CH₂NBu^t]AlH₂}_n]via elimination of lithium hydride. The aluminium triamide and the cis and trans isomers of the dimeric aluminium diamide have been structurally authenticated.