Reactions with Dimetallic Compounds

Palladium-catalysed reactions of dimetallic compounds 358 such as X2B—BX2, R3Sn—SnR3, R3S11—SiR3 or R3Si—SiR3 with halides via oxidative addition and transmetallation are useful for the preparation of carbon main group metal bonds 359. 

The trialkylsilyl group can be introduced to aryl or alkenyl groups using hexaalkyldisilanes. The oxidative addition of alkenyl iodide and transmetallation, 

Under certain conditions, aroyl chlorides are converted to arylsilanes by the reaction with disilanes. The oxidative addition of aroyl chloride and decarbonylation are followed by transmetallation and reductive elimination to give aryl silanes. Neat trimellitic anhydride acid chloride (377) reacts with dichlorotetramethyldisilane (376) at 145 °C to generate 378, which affords 4-chlorodimethylsilylphthalic anhydride (379) by reductive elimination. Finally it was converted to 380 and used for polyimide formation [185], Biphenyltetracarboxylic anhydride 381 is obtained at a higher 

Unexpectedly, the arylsilane 383 can be prepared by the Pd-catalyzed reaction of aryl halides with the hydrosilanes 382, without giving the expected hydrogenolysis product 384 [186], 

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Three transmetallation reactions are known. The reaction starts by the oxidative addition of halides to transition metal complexes to form 206. (In this scheme, all ligands are omitted.) (i) The C—C bonds 208 are formed by transmetallation of 206 with 207 and reductive elimination. Mainly Pd and Ni complexes are used as efficient catalysts. Aryl aryl, aryl alkenyl, alkenyl-alkenyl bonds, and some alkenyl alkyl and aryl-alkyl bonds, are formed by the cross-coupling, (ii) Metal hydrides 209 are another partner of the transmetallation, and hydrogenolysis of halides occurs to give 210. This reaction is discussed in Section 3.8. (iii) C—M bonds 212 are formed by the reaction of dimetallic compounds 211 with 206. These reactions are summarized in Schemes 3.3-3.6. 

Rare kinds of substitution polycondensations also include reaction of dihalides with dimetallic compounds ... 

The 1,1-dimetallic compounds, R2C(SnMe3)ZnBr, were oxidized by dry air at —10 to 0°C in the presence of Me3SiCl to give aldehydes or ketones, R2C=0. In a related indirect method, arylthallium bis(trifluoroacetates) (prepared by 12-21) can be converted to phenols by treatment with lead tetraacetate followed by triphenylphosphine, and then dilute NaOH. Diarylthallium trifluoroacetates undergo the same reaction. ... 

The reactivity of the dimetallic compounds 186a and 186b was then investigated and these species were less reactive than their formulas would lead to predict, as no reaction occurred with ketones, esters, Michael acceptors or trimethylsilyl chloride. In the presence of BF3 OEt2, addition occurred to aldehydes and led after /3-elimination to the corresponding olefination products 189 with good to excellent (E) stereoselectivity (equation 92)127. 

Addition reactions of three kinds of main group metal compounds, namely R—M X (carbometallation, when R are alkyl, alkenyl, aryl or allyl groups), H—M X (hydrometallation with metal hydrides) and R—M —M"—R (dimetallation with dimetal compounds) to alkenes and alkynes, are important synthetic routes to useful organometallic compounds. Some reactions proceed without a catalyst, but many are catalysed by transition metal complexes. 

Mechanism Two pathways are suggested for this reaction (Scheme 4.49). The titanium-carbene complex A is formed as a key intermediate, which reacts with carbonyl compound to form an alkene via the oxatitanacyclobutane B (Path A). Alternatively, the addition of gem-dimetallic species C to a carbonyl compound gives the adduct D, which eliminates (TiCp2 RS)20 to give an alkene (Path B). 

Substituted gem-dimetallic compounds, readily obtained via allylation of alkenyl organometallics, react with aldehydes in the presence of BF3-Et20 but do not react with ketones. When alkylidenemalonates are used instead of aldehydes, the Z-olefins see (E) (Z) Isomers) are obtained with a very high stereoselectivity (Scheme 35). A transmetallation reaction with copper cyanide significantly increases the reactivity of gm-dimetallic derivatives via formation of 1,1-zinca cyanocuprates. Indeed, when these compounds react with... 

Sulfenylation of 1,3-dicarbonyl compounds. Dimetalated 1,3-dicarbonyl compounds, prepared by use of 1 equiv. each of NaH and n -C4H9Li or with 2 equiv. of LDA, are converted into 4-phenylthio-l,3-dicarbonyl compounds by reaction with CftHsSCl, QHsSSCeHs, or C6H5SO2SQH5. Yields are 50-80%. and are not improved by added HMPT. 

In most cases the excess of starting compound can be readily separated from the derivatization product by distillation. Problems may arise, however, when a substrate with a relatively high molecular weight is to be metallated and subsequently functionalized, since the difference in the boiling points of the starting compound and end product is then much smaller. In such a case one may consider to perform the metallation with an excess of base (if there is no chance on dimetallation or other complications) and to destroy the excess by reaction with THF at somewhat higher temperatures (resulting in the formation of H2C=CH2 and H2C=CH—OM) prior to the further synthetic operations. Such a consideration also makes sense when the substrate is expensive or not readily available. 

Dimetallation of alkynes also provides a practical synthesis of thiophenes. Dimetallation of (1-naphthyl)ethyne, reaction with elemental sulfur, and quenching of the reaction with r-butanol affords the thiophene (20) in one pot (Scheme 7) <89SC269l>. In another example, the alkynes (21 R = MeS, MeO, Bu O, MejN, Et2N) were dimetallated, treated with non-enolizable thiocarbonyl compounds (R = Bu, Ph, 2-thienyl, MeO, Bu O, Et2N), and quenched with /-butanol to give (22), which eliminate methanethiol spontaneously to afford a series of 3,4-disubstituted thiophenes (23) in good yields (Scheme 8) <90SC3427>. Meanwhile, metallation of a 4 1 mixture of the ynamine and... 

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. 

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