Gallium silyls

The hypersilyl group allows isolation of stable gallium silyl compounds with tri- and tetracoordinated gallium centres. The GaSi bond seems to be inert to protic reagents. 

Keywords Gallium Silyls / Digallanes / Gallium(I) compounds... 

Tris(trimethylsilyl)silane [20,21], thiols [22], germanes [23-25] and gallium hydride [26] can be added easily to terminal alkynes in the presence of Et3B/02. This process was extended to internal alkenes (Scheme 8, Eq. 8a) as well as silyl enol ethers (Eq. 8b) by using tri-2-furylgermane. In this last case, basic or acidic treatment of the main syn /J-siloxygcrmanc furnishes the corresponding E- or Z-alkene, respectively [24],... 

Treatment of silyl enolates with methyllithium followed by an addition of gallium trichloride affords the corresponding gallium enolates. The reaction of the resulting gallium enolates with a-halo carbonyl compounds in the presence of triethylborane provides 1,4-dicarbonyl compounds in good yields (Scheme 142).433... 

This chapter is primarily concerned with keto-enol equilibrium and the chemistry of dissociated enols (enoxides) and lithium enolates. The acid-base aspects of the chemistry of other metal enolates (e.g. silyl enol ethers "", boron enol ethers" " " , aluminium , tin " , gallium , bismuth , zinc " ", rhodium , palladium " , manganese ", copper , nickel , magnesium " , titanium " , molybdenum , zirconium" " and ammonium" " enolates) have been reported elsewhere. 

The Use of the Tris(trimethylsilyl)silyl Group in Stabilization of Low Valent Gallium Compounds... 

We will present the use of the tris(trimethylsilyl)silyl group (hypersilyl) [14] to stabilize low valent gallium species. 

Table 1. Bond lengths [pm] as results of ab initio (SCF) calculations on silyl gallium compounds.

Unusual orientation has been observed by Yamaguchi in electrophilic aromatic substitution using gallium trichloride. The reaction of toluene and bis-silylated 1,3-butadiyne gives an o-substituted product exclusively (Scheme 7.4), and even isopropylbenzene reacts at the o-position predominantly [15]. The tendency of the reaction to occur at the vicinity of the alkyl substituent is, however, restricted to the diyne-based electrophile for other related electrophiles derived from silylethyne, si-lylallene, or bissilylated 1,5,5,7-octatetrayne normal o/p orientation is observed. 

Gallium enolate and ethynylgallium, generated, respectively, from silyl enol ether and silylethyne by treatment with gallium trichloride, undergo carbogalla-tion, giving a-ethenylated ketones after work-up with aqueous acid (Scheme 7.28)... 

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