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

The alkylaluminate [Li(THF)(2)AlH3C(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)(2)AlH3R](2) (R = C(Si Me3)(3) (1), or C(SiMe2Ph)(3) (2)). The Al and Li atoms an linked by hydrid e bridges and the NMe2 groups are not coordinated to metal centres. The com pound 1 reacts (i) with one equivalent of SiMe3Cl to give the cyclic dialum inate Li(THF)(2)(mu-H)AlHR(mu-H)AlHRH (4) (characterised by an X-ray study) ; (ii) with two equivalents of SiMe3Cl to give the alane-THF complex (Me3Si )(3)CAlH2. THF (5); and (iii) with an excess of pyrazole to give [LiAlH(C3H 3N2)(2)C(SiMe3)(3)](2) (7), in which Al and Li atoms are linked by both hyd ride and pyrazolato bridges. The compound (Me2PhSi)(3)CAlH2. THF (6) has be en obtained by the reaction of 2 with two equivalents of SiMe3Cl. (C) 2000 Elsevier Science S.A. All rights reserved.