Alkali Metals and Magnesium

Allylpotassium derivatives exist in two stereoisomeric (endo or exo) forms.239,240 Although the endo isomer is more stable, the equilibration is slow enough to allow the synthesis of stereoisomeric heterosubstituted derivatives [Eqs. (10.42) and (10.43)]. On the other hand, even the E-alkenes after appropriate equilibration can be transformed to Z-boron compounds 10  

Bromoalkynes, which are important intermediates in coupling reactions,241 can be synthesized through the corresponding metalated alkynes 241,242 

Heterosubstitution at nonactivated positions is also possible by using highly reactive metalating agents such as pentylsodium. When used in the presence of tm-BuOK, it readily and selectively forms vinylsodium derivatives that can subsequently be converted to organosilicium compounds.243 Norbomadiene and bicyclo-[3.2.0]hepta-2,6-diene are also readily silylated via the corresponding sodium compounds formed in the reaction with BuLi-rm-BuONa.244 Similar transforma-tions of strained polycyclic cyclopropanes were also achieved [Eq. (10.45) ]  

Excellent selectivity was observed in the silylation of 1,3,5-cycloheptatriene giving 2-(trimethylsilyl)-l,3,5-cycloheptatriene as the sole product 244 

With the extremely efficient metalating agent B uLi-ferf-B uOK-TMEDA even direct metallation of ethylene and the transformation of the intermediate to hetero-substituted product were accomplished 246 

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Chemically, carbon dioxide is not very reactive, and it is often used as an inactive gas to replace air when the latter might interact with a substance, for example in the preparation of chromium II) salts (p. 383). Very reactive metals, for example the alkali metals and magnesium can, however, continue to bum in carbon dioxide if heated sufficiently, for example... 

D.S. Stasinevich, G.A. Egorenko, Thermographic investigation of alkali metal and magnesium tetrahydroborates at pressures up to lOatm , Russ. J. Inorg. Chem. 13 (1968) 341-343. 

Alkali metals and magnesium react with 54a at room temperature in THF to form, selectively and in quantitative yield, the 1,3,4-triphospholides M[3,5-Bu 2-l,2,4-C2P3] 152 (M = Li, Na, K orMg2(/r-Cl)3(THF)6). The intermediacy of the symmetric dimer P6(CBu )4 151 in this process was evidenced by P H NMR spectroscopy in dg-THF. In keeping with this, reduction of 54a with the lanthanides Sm or Eu afforded 151, the structure of which, however, has not been unequivocally assigned (Scheme 49) <2005OM5789>. 

Using isolated intact epithelial mucosal preparations, we have shown that, when lithium associated with the extracellular space was taken into account, acute cellular uptake of lithium was negligible (172). This is confirmed by experiments on lithium efflux from everted rings of rat jejunum (173). The recognition that intestinal uptake and transport of lithium may not involve transcellular transport of the metal agrees with proposed transport mechanisms for other alkali metals and magnesium (174). Metal-ion carrier proteins are not essential for rapid absorption of metals to occur their function is to assist when existing equilibrium conditions are unfavorable. 

In sodium (the second alkali metal) and magnesium (the second alkaline earth metal), electrons are added to the 35 sublevel, which contains the 35 orbital only, just as they filled the 2s sublevel in lithium and beryllium in Period 2. Then, just as for boron, carbon, and nitrogen in Period 2, the last electrons added to aluminum, silicon, and phosphorus in Period 3 half-fill the three 3p orbitals with spins parallel (Hund s rule). The last electrons added to sulfur, chlorine, and argon then successively enter the three half-filled 3p orbitals, thereby filling the 3p sublevel. With argon, the next noble gas after helium and neon, we arrive at the end of Period 3. (As you ll see shortly, the 3d orbitals are filled in Period 4.)... 

Davis, D. D., Gray, C. E., Alkali Metal and Magnesium Derivatives of Organo-Silicon, -Germanium, -Tin, -Lead, -Phosphorus, -Arsenic, -Antimony and -Bismuth Compounds, Organometal. Chem. Rev. A 6 [1970] 283/318. 

For the enolates of alkali metals and magnesium, their known tendency for aggregation was put forward against the Zimmerman-Traxler model that assumes monomeric enolates as the reactive species. However, even the aggregation is compatible with the model if one assumes a sbc-membered transition state to operate at tetrameric lithium enolates, as postulated by Seebach and coworkers [74]. The fact that a more precise cis-sy -correlation is observed for enolates of boron, titanium, or tin is also compatible with the Zimmerman—Traxler model. For these stronger Lewis acids (compared to alkali metals or magnesium), the six-membered transition state will be tighter, so that steric effects become more important. 

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