Syntheses of some bulky alkylalanes and alkyltrihydroaluminates: crystal structures of [Li(THF)2AlH3C(SiMe3)2(SiMe2NMe2)]2, Li(THF)2Al2H5{C(SiMe3)3}2, (Me3Si)3CAlH2·THF and the pyrazolato derivative [LiAlH(C3H3N2)2C(SiMe3)3]2 (THF=tetrahydrofuran)

The alkylaluminate [Li(THF)2AlH3C(SiMe3)2(SiMe2NMe2)]2 (3), obtained by the reaction between [LiC(SiMe3)2(SiMe2NMe2)·2THF] and LiAlH4, has a cyclic structure like those of the compounds [Li(THF)2AlH3R]2 (R=C(SiMe3)3 (1), or C(SiMe2Ph)3 (2)). The Al and Li atoms are linked by hydride bridges and the NMe2 groups are not coordinated to metal centres. The compound 1 reacts (i) with one equivalent of SiMe3Cl to give the cyclic dialuminate (4) (characterised by an X-ray study); (ii) with two equivalents of SiMe3Cl to give the alaneTHF complex (Me3Si)3CAlH2·THF (5); and (iii) with an excess of pyrazole to give [LiAlH(C3H3N2)2C(SiMe3)3]2 (7), in which Al and Li atoms are linked by both hydride and pyrazolato bridges. The compound (Me2PhSi)3CAlH2·THF (6) has been obtained by the reaction of 2 with two equivalents of SiMe3Cl.