From dimetallic compounds

Other group 4A organodimetallics (RjMM Rj M=M =Si, Sn, Ge) is also described [92] via their corresponding radical cations, generated by ET from dimetallic compounds to the excited AcrH+. However, if M = M = Si, two electron reductions of AcrH is normally observed [93] because of the lower reducing ability of Me3Si compared with McjSn and MejGe. ... 

The violence of superbasic slurries towards functionalized organic molecules means that they are at their most effective with simple hydrocarbons they also tolerate ethers and fluoro substituents. LiCKOR will deprotonate allyUc, benzylic, vinylic, aromatic and cyclopropane C—H bonds with no additional assistance. From benzene, for example, it forms a mixture of mono and dimetallated compounds 617 and 618 (Scheme 241) . ( Li/K indicates metallation with a structurally ill-defined mixture of lithium and potassium.)... 

A molecular structure, similar to that of hexasilylated benzene derivative 229, was obtained from tetracyclic hexasilylbenzene 230 by Kira, Sakurai and coworkers, where the six silicon centres are incorporated in three five-membered ring systems (Scheme 80) °. In dimetalated compound 231, two lithium centres, coordinated by a quinuclidine ligand each, are capping the phenyl ring plane from both sides in the solid state. Moreover, it could be found that compound 231 has a thermally accessible triplet state, investigated by temperature-dependent ESR spectroscopy °°. 

Cyclic oligostannacycloalkanes, [R2Sn(CH2) ]m, can be prepared from the reaction between tin dihalides and organodimetallic compounds, or tin dimetallic compounds and organic dihalides. Many of these reactions give mixtures of oligomers from which the individual compounds are separated, usually by chromatography, and sometimes in only low yield (e.g. equation 10-18).11... 

Other mixed g e/H-dimetallic compounds containing zinc and either zirconium, aluminum, or titanium have been successfully prepared from alkynylzinc halide compounds via hydrozirconation by H(Cl)ZrCp2 (the Schwartz s reagent) or carbometalation by a combination of Me3Al/Cp2TiCl2 (Scheme 15). 

We have synthesized some novel silarylene and silarylenesiloxane polymers via dicarbanions prepared from Lochmann s base. Lochmann s base, a powerful metalating reagent composed of equimolar amounts of n-butyl lithium and potassium r-butoxide in a hydrocarbon, has been used to dimetalate compounds such as m-xylene, 4,4 -dimethylbi-phenyl, and 2,3-dimethyl-1,3-butadiene in good yields. In this work the dicarbanion of m-xylene and 4,4 -dimethylbiphenyl have been used to prepare silicon containing monomers and polymers by two different routes. The first route involves a 1 1 condensation reaction between the dicarbanion and a dichlorodiorganosilane to produce a condensation polymer. The second route involves reaction of the dicarbanion with a chlorodiorganosilane which is then converted to a bis(silanol) and then polymerized. Spectroscopic as well as thermal characterization will be presented on the polymers which have been described. 

The dilithiation can be carried out with BuLi in Et20 or THF at temperatures varying from about -20 C for R = R S, Ph, vinyl, to +30 C in the case of aliphatic hydrocarbons [42], Dimetallation of the latter compounds also proceeds excellently with BuLi.TMEDA in refluxing hexane [43],... 

Treatment of isopropenylacetylene with an excess of BuLi or BuLi.TMEDA does not give rise to double deprotonation, but to a slow addition with formation of an adduct With the super basic reagent BuLi.r-BuOK [45,46,52,53] in a mixture of THF and hexane, dimetallation can be accomplished in a short time at low temperatures. The high efficiency of the dimetallation appears from the excellent yield (> 90%) of MejSiCsCC(CH2SiMe3)=CH2 obtained by quenching with h SiCl. Addition of anhydrous lithium bromide converts the dipotassium compound into the dilithio derivative, which can be used for regiospecific functionalizations. 

Thus, the alkenyllithium reagent derived from the (X)-y-iodo allylic ether 205 underwent addition of crotylzinc bromide in ether at — 50 °C and, after hydrolysis of the resulting dimetallic reagent, compound 206 was obtained with high diastereoselectivity (anti/syn = 93/7) (equation 101)146. 

Combining substrate-induced diastereoselection and mutual diastereoselectivity, as illustrated for the crotylzincation of the alkenyllithium derived from 209, led to excellent results as the gewt-dimetallic species 217 was obtained in a highly stereoselective fashion. The stereochemical outcome was explained by the addition of the kinetically reactive cisoid metallotropic form of the crotylzinc reagent anti to the propyl group in the chelated allyl alkenylzinc intermediate. After hydrolysis, compound 218 was obtained as a single diastereomer (equation 106)148,149. 

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