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

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(ButNCH2CH2NButH)]. This compound reacted with an additional equivalent of AlH3·NMe3 to yield the dibridging amidoalane complex [(AlH2)2{µ-N(But)CH2CH2N(But)}] or a molecule of the diamine to give the triamidoaluminium species [Al(ButNCH2CH2NBut)(ButNCH2CH2NButH)]. In the absence of an excess of AlH3·NMe3 or N,N′-di-tert-butylethylenediamine, [AlH2(ButNCH2CH2NButH)] eliminates molecular hydrogen to give the trans isomer of the dimeric diamidoalane complex trans-[{AlH[µ-N(But)CH2CH2NBut]}2] which is stable toward reaction with either of the reactants. A stable analogue of the intermediate [AlH2(ButNCH2CH2NButH)] 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(But)CH2CH2NBut]}2] was prepared from the unstable lithium diamido aluminium hydride species [{Li[N(But)CH2CH2NBut]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.