Halides metal stannyls

Metalated ferrocenes also serve as convenient precursors to ferrocenylboranes. Lithiated ferrocenes have been ntilized for the preparation of ferrocenylboronates FcB(OR)2 and l,T-fc(B(OR)2)2 and are especially suitable in the presence of ort/ o-directing donor-substituents. The borylation of disilylated ferrocenes with excess BCI3 on the other hand was reported to yield varying amounts of 1,3-diborylated prodnct (82 M = Fe, X = Cl) in addition to the l,F-diborylated species (83 M = Fe, X = Cl). In contrast, when 1,F-distannylated ferrocenes were treated with equimolar amounts of boron halides, l-stannyl-2-borylferrocenes (86) were formed as the major product rather than the expected... 

Ligand substitutions of 18-electron complexes can also occur by radical-chain processes initiated by atom abstraction. These radical chains occur through 17-electron intermediates that imdei o facile associative substitutions. Substitutions of metal carbonyl hydrides, halides, and stannyl complexes by this mechanism are all known. These reactions are particularly prevalent in first-row metal hydrides because the M-H bond is weaker than the M-H bond in second- and third-row metal complexes, and hydrogen atom abstraction is one step of the radical chain. However, they have also been proposed to occiu with third-row metal-hydride complexes... 

Germyl, Stannyl, and Plumbyl Anions The preparative methods for the synthesis of the germyl, stannyl, and plumbyl anions are essentially the same as those mentioned above for the silyl anions. The most widely used methods are (1) reduction of halides R3EX (R = alkyl, aryl E = Ge, Sn, Pb X = Cl, Br) with alkali metals and (2) reductive cleavage of the E-E bond of R3E-ER3 (R = alkyl, aryl E = Ge, Sn, Pb) with alkali metals or organolithium reagents. Due to the favorable polarization of the (E = Ge, Sn, Pb) bond, the direct metalation... 

In the first systematic study on nucleophilic substitutions of chiral halides by Group IV metal anions, Jensen and Davis showed that (S )-2-bromobutane is converted to the (R)-2-triphenylmetal product with predominant inversion at the carbon center (Table 5)37. Replacement of the phenyl substituents by alkyl groups was possible through sequential brominolysis and reaction of the derived stannyl bromides with a Grignard reagent (equation 16). Subsequently, Pereyre and coworkers employed the foregoing Grignard sequence to prepare several trialkyl(s-butyl)stannanes (equation 17)38. They also developed an alternative synthesis of more hindered trialkyl derivatives (equation 18). 

Methyl-1,2,4-diazaphosphole (6) is metallated by butyllithium selectively in the 5-position <87JOM(3l9)49>. From the subsequent reaction with an electrophilic element halide, 5-methyl-, 5-stannyl-, and 5-boryldiazaphospholes (7) are obtained <87JOM(3l9)49,87TH 422-01 >. Catalytic amounts of potassium t-butoxide in acetonitrile-i/j effect an H/D-exchange, fast in the 5-position and slow in the 3-position of 1-phenyl-1,2,4-diazaphosphole <87JOM(3l9)49>. 

Bulky stannyl anions which are not available from stannyl hydrides (see Section I.A.l) were prepared by using the reaction of alkali metals with tin halides (equations 24 - 26)31,40 41. 

When Me3SiSnBu3 is treated with CsF, the fluoride anion should coordinate to the silyl group and not the stannyl group to produce a hypervalent silicate, and as a result, a stannyl anion would be generated.282 The stannyl anion reacts with vinyl iodide to produce a vinyl anion via a halogen-metal exchange and it reacts with the carbonyl group intramolecularly (Equation (113)). Aryl halides or allyl halides are also used in similar cyclizations.283,284... 

Hexamethylditin is a suitable reagent for Pd-catalyzed metallation of aryl-halides to furnish aryltin compounds that in turn can react in Stille couplings with aryl halides to form biaryl derivatives. Hitchcock and coworkers [ 126] have shown that 2-pyridyl triflate and (hetero)aryl bromides can be coupled to 2-(hetero)aryl pyridines 174 in moderate to good yields (Scheme 66). The underlying principle of this heterocoupling of two aryl (pseudo)hahdes is the selective stannylation of the triflate that is undergoing a faster oxidative addition to the Pd(0) complex than the bromide. 

For the fast ge/w-dialkylation of 1,3-dithiane dianion, tin-lithium transmetallation at the 2-position of dithiane is a much faster process than the corresponding deprotonation. 2,2-Bis[tri(n-butyl)stannyl]dithiane (175)223 can be alkylated sequentially it was trans-metallated with n-BuLi at —78 °C, after 5 minutes treated with the first alkyl halide and after 10 more minutes the process was repeated providing dialkylated products224. This strategy has been used in the total synthesis of (—)-perhydrohistrionicotoxin, namely preparing the key compound 178 employing successively iodides 176 and 177 as electrophiles (Scheme 50)224. 

This method was applied to the diastereoselective synthesis of vinyl ethers from readily available a-alkoxy aldehydes9. Reasonable selectivity in favor of the syn-adduct is observed when the stannyl anion is modified by softer metal salts such as zinc halides or copper(I) bromide. 

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