Base-free alkali metal hydrocarbyls

The structures of base-free hydrocarbyls of the alkali metals have been investigated much less than those of the solvated species [4], The first example of an unsolvated dimer was [LiC(SiMe3)3]2,1 [5]. This pyrophoric compound was prepared by reacting the corresponding HgBr derivative with n-butylhthium. 

In a cubic giant unit cell 24 tetrameric (NaMe)4 units form a zeolitic host lattice. This structure is related to that of methyllithium, but the arrangement of the tet-ramers is more complicated. It results in the presence of large cavities, in which (LiMe)4 units can be intercalated up to the structurally predetermined molar ratio of 3 1. In this sense the host-guest compound (NaMe)4 [(LiMe)4]4 x 0.333), 39, was termed the first organometallic supramolecular compound . 

The higher lithium alkyls (LiBu )4, 29 [6], and [Li(l-norbornyI)]4, 30 [30], have also been reported to be associated as tetramers in the solid state. In the crystal, t-butyllithium is a tetramer with approximate symmetry. Each face of the Li4 tetrahedron is capped by a t-butyl unit with the methyl groups being in an ecliptic position relative to the hthium triangle. 

Self-assembly to form polymeric aggregates has also been found in the chemistry of base-free organoalkali metal compounds. An interesting example is the crystalline, hexane-soluble sodium alkyl [Na U-CH(SiMe3)2 ] , 60, prepared by reaction of 

---