Organosodium complexes

In contrast with the low reactivity observed with n-butyllithium solutions in hydrocarbons (5) or ether (6), the n-butyllithium-amine adducts rapidly metalate unsaturated hydrocarbons including even simple olefins. In this respect they surpass even organosodium compounds and will probably prove to be of considerable synthetic value. Addition of a hexane solution containing equimolar amounts of n-butyllithium and an amine to excess toluene at ordinary temperatures results in rapid formation of a benzyllithium-amine complex that in some cases separates as a yellow crystalline solid. 

Finally, a recent report demonstrates the very powerful metalating abilities of N-chelated organosodium complexes. Trimitsis et al. (54) found that an equimolar amount of TMEDA and n-amylsodium form a bright-blue suspension capable of converting dimethylarenes quantitatively into their a, -dianions at room temperature within two hours. Both 1,3-dimethylnaphthalene and m-xylene reacted with two equivalents of n-AmNa-TMEDA to form the corresponding disodium reagents in over 90% yield. This area also seems attractive for further study. 

From their study of the reactions of organic halides with organosodium complexes in dioxane solution, Morantz and Warhurst (97) concluded that the measurements could be reconciled only with the concept of ion pairing. They concluded that the solutions contained exclusively the monomeric form of the radical anion paired with the alkali metal cation. The influence of the alkali ion on the electronic spectra was investigated by Carter et al. (100). They measured the absorption spectra in the region 10,000-25,000 cm of a number of alkali metal complexes in dioxane solution and found that for a given radical anion the frequency of the maximum of an absorption peak shifted towards the red as the radius of the alkali metal cation increased. A relation was found between this frequency and the radius of the cation... 

The other system is the polymerization carried out in polar ethereal media at temperatures lower than -40 °C to avoid the undesirable side reaction of media with anionic initiators and chain-end anions. The condition in tetrahydrofuran (THF) at -78 °C is among the most employed system. In polar media, not only RLi but also organosodium and organopotas-sium compounds can be used as initiators. Furthermore, radical anion complexes formed by aromatic hydrocarbons and alkali metals are often used as difrmctional initiators. In the propagating chain-end anion in polar media, there is equilibrium among several ion pairs and a free ion, each of which can participate in the propagation reaction. 

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