Sterically encumbered lithium dialkynidoalanates Li[R 2 Al(–C≡C–R’) 2 ] [R=CH(SiMe 3 ) 2 ]

Bis[bis(trimethylsilyl)methyl]aluminium chloride, [(Me₃Si)₂CH]₂Al–Cl, reacted with two equivalents of the lithium alkynides Li–C≡C–R (R=CMe₃, C₆H₅) and formed the corresponding alanates Li{[(Me₃Si)₂CH]₂Al(–C≡C–R’)₂} (1: R=C₆H₅; 2: R=CMe₃), both of which were characterized by crystal structure determinations. Interestingly, a similar ether adduct (3) was formed by the treatment of the trialkylalane Al[CH(SiMe₃)₂]₃ with Li–C≡C–C₆H₅. The lithium atoms of all compounds are coordinated to both carbon atoms of the triple bonds with the shortest distance to the carbanionic carbon atoms of the alkynido groups. While compounds 1 and 2 form one-dimensional coordination polymers through intermolecular interactions between Li atoms and CH₃ groups, an ether molecule attached to the lithium atom of monomeric 3 prevents its polymerization.