Polylithium compounds

Mulvaney and coworkers reported a polylithiation of a non-terminal acetylene for the first time, more exactly the formation of CeHsCBLiB and CeH4LiC3Li3 from 1-phenylpropyne and n-butyllithium in hexane" . Stimulated by their work. West and Gornowicz prepared and investigated new polylithium compounds from phenylpropynes and their polysilicon derivatives . The structures of several of them were analysed by IR spectroscopy. 

Moreover, in deprotonation reactions with common alkyllithium bases (e.g. butyl-lithium), no side-products are formed, that increase the solubility of the polylithium compound. Also, product mixtures are only rarely observed with this method. Thus, the resulting polylithium compound can be isolated or crystallized more easily. This is why—in addition to Section II. E—only this section presents many visualizations of successful X-ray structural analyses of polylithiated compounds. 

By the analogous reaction, the doubly lithiated sulphur substituted vinyllithium compound 126 was generated by Brandsma, Maercker and coworkers, starting from tellura-cycle 125. An interesting pathway to functionalized heteroatom-substituted polylithium compounds has been introduced by this method (Scheme 46). 

By extension and application of this method, which our group is using for the preparation of silacycles , polysilacage molecules have been synthesized by Shimizu and coworkers, using the polylithium compounds 170-172 as building blocks (Figure 21) . 

The first reported polylithium compound, dilithiomethane, is obtained in 6% yield by the reaction of dibromethane with lithium. Higher yields are obtained by pyrolyzing methyllithium tetramer in the solid state. This procedure is improved by conducting the reaction under vacuum with rapid stirring . The temperature must be carefully monitored because heating above 250°C leads to rearrangement to secondary products. Furthermore, better results are obtained with methyllithium that is not complexed with LiBr. 

Lithiation of 3-phenylpropyne produced similar polylithium compounds. With three equivalents of n-butyllithium in cyclohexane, 3-... 

Sneddon, LG. and Lagow, R.J. (1975) Vapour synthesis of polylithium compounds the effect of halogens in activating the carbon-hydrogen bond. J. Chem. Soc., Chem. Commun., 302-303. 

Conceptually, when two carbon-metal bonds are in the same molecule and in close proximity, these two carbon-metal moieties may exhibit novel reactivity. A few of 1,4-dilithio compounds are developed and used as 1,4-dianion precursors for the preparation of main group metaUole [22]. Besides, some dilithium or even polylithium compounds show interesting reactivity [7-21]. For example, bis (2-lithioallyl)amines [15], 2,9-dilithio-l,4,6,9-decatetraenes [16], 3,4-dilithio-... 

---