ALKALI-METAL DERIVATIVES

The lithium alkyls are extremely reactive. They are very sensitive to oxygen and moisture. Dry apparatus and dry solvents must be used and air must be excluded by working under an atmosphere of dry oxygen-free nitrogen or argon. The following methods of preparation are available. 

The physical state of the lithium is important and reaction does not start if the metal is too coated with corrosion product. Lithium is now supplied as a dispersion in mineral oil which can be weighed in air. The oil is removed by washing with hexane under an inert atmosphere, leaving the metal as a highly reactive, pyrophoric powder. 

One of the most frequently used reagents is n-butyllithium, which can be prepared from chloro- or bromobutane in hexane, benzene or ether. Solutions in hexane (usually 3.6moldm BuLi) are commercially available. Methyl chloride, bromide and iodide all react satisfactorily with lithium in diethyl ether. Normally alkyl iodides are unsuitable as they react too quickly with the organolithium compound RI + RLi - R—R + Lil. A similar problem arises with benzyl chloride, which gives 1,2-diphenylethane. Aryl bromides and iodides, however, often give good yields, although the chlorides are often insufficiently reactive. 

Organolithium reagents attack ethers, although in some cases (e.g. MeLi in diethyl ether) only very slowly. Because of such side reactions and the greater sensitivity of organolithiums to air and moisture, the use of Grignard reagents is usually more convenient, if they also perform the desired reaction (p. 44). 

The reaction goes to the right if the hydrocarbon R H is more acidic than RH (or RjNH). In Table 3.3 the pK values of some hydrocarbons, a measure of their acidities, are listed. Phenylethyne, for example, reacts with either butyl- or phenyllithium 

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Several methods for the preparation of unsymmetrical sulfur diimides RN=S=NR have been developed. One approach involves the addition of a catalytic amount of an alkali metal to a mixture of two symmetrical sulfur diimides, RN=S=NR and RT8i=S=NR. A second method makes use of alkali-metal derivatives of [RNSN] anions.Eor example, derivatives in which one of the substituents is a fluoroheteroaryl group can be prepared by the reaction of the anionic nucleophile [RN=S=N] with pentafluoropyridine. Sulfur diimides of the type RN=S=NH (R = 2,4,6- Bu3C6H2S) have also been prepared. "... 

The equilibrium situation for simple substituted 2-ulkenyl alkali metal derivatives can be estimated by a rule of thumb electron-accepting and electropositive substituents ( ) prefer the exo position, but electron-donating and electronegative substituents ( ), including alkyl groups, tend to occupy the endo position. With increasing steric demand of the substituent, the exoisomer becomes more favored. 

Various alkali metal derivatives Various dialcohols and diacids 123,164)... 

Diesters of phosphorous acid are in general neutral because the phosphorous acid exists mostly in the phosphonate form with one hydrogen directly attached to the phosphorus. But with alkali metals the H can be changed against the alkali and reactive intermediates formed. Such alkali metal derivatives of dialkyl phosphites react with alkyl halides to give dialkyl alkanephosphonates, according to Eqs. (45) and (46). 

Alkali metal derivatives of A/ ,N -diarylformamidines form a particularly well investigated class of compounds. Most recently, in 2007, the fascinating structural... 

Alkali metal derivatives of 2-(trimethylsilyl)aminopyridines can be further derivatized by insertion of 1,3-dicyclohexylcarbodiimide. Functionalized guani-dinates are formed in this reaction via a 1,3-silyl shift. Scheme 170 illustrates the reaction sequence as well as the preparation of an aluminum complex of the modified ligand, which exhibits pseudo jS-diketiminate binding of the metal center, thus exemplifying the coordinative versatility of this new multi-N-donor system. ... 

Synthetic and mechanistic aspects of the reactions of the alkali-metal derivatives of organotin compounds, RaSnM ("organostannylan-ionoids ) have been reviewed (79, 80). They may be prepared by reactions of the types shown in the following equations. 

Limitations common to both salt elimination methods 1 and 2 are (a) the required product may be difficult to separate from the alkali metal halide, (b) reactions are best carried out in the solvent (usually an ether) in which the initial alkali metal derivative is prepared, (c) difficulties may arise through metal-halogen exchange (207), and (d) the range of starting anions is limited [e.g., X3Si compounds are only readily formed when X = H or Ar,... 

Alkali Metal Derivatives of Metal Carbonyls, 2, 1S7 Alkyl and Aryl Derivatives of Transition Metals, 7, 1S7 Alkyl cobalt and Acylcobalt Tetracarbonyls, 4, 243 Allyl Metal Complexes, 2, 32S... 

See ALKALI-METAL DERIVATIVES OF HYDROCARBONS See Other METAL ACETYLIDES... 

Besides these alkali metal derivatives, partially halogenated cyclosilanes were necessary for these syntheses. The preparation of such compounds is sometimes very troublesome and a description of these routes would be too long for this review, but most of these syntheses have been published [13]. The separation of the isomers is sometimes very difficult and can be made via derivatives with large... 

A further significant factor slowing the development of the chemistry of the heavy alkali metal derivatives has been the high reactivity of the complexes, with frequent attack of the ethers used to break up the aggregates in hopes to achieve increased solubility. In fact, ether cleavage is a common observation and manipulations at very low temperatures are often required to overcome this issue.9 Ether cleavage may also be suppressed by the introduction of nitrogen-based donors such as TMEDA and PMDTA. 

Alkali Metal Derivatives with Heavy Group 14 Ligands 2.01.3.1 Alkali Metal Silanides... 

Since then, several different alkali metal silanide systems have been reported. One of them, the hypersilyl [Si(SiMe3)3] ligand, was first prepared by Gilman and Smith.172, 173 Another ligand includes supersilyl [SPBuJ-prepared in 1975.174-176 Several other variations of the ligand systems are known with the recent addition of [SkB Ph]-, for which several alkali metal derivatives have been prepared and characterized.177,178... 

The tris(trimethylsilyl)silyl ligands can be easily modified by reactions with silyl chlorides, as shown with a series of phenylated species Mes Ph SiCl (n = 0-3). Furthermore, triisopropyl, thexyldimethylsilyl, or tert-butyldimethylsilyl substitution are all easily possible.190 The crystallographic characterization of some of the alkali metal derivatives indicates a direct correlation between ligand size and resulting structural parameters. 

Silver and thallium salts of pyrazolylborates provide cleaner routes to metal complexes of these ligands than alkali metal derivatives. The silver complex [HB 3,5-Pz(CF3)2 3]Ag(THF), for example, reacted with diethylzinc to afford [HB 3,5-(CF3)2Pz 3]ZnEt 106, shown in Figure 52, as the sole product.164... 

Sulfur diimides react quantitatively with organolithium reagents at the sulfur centre to produce lithium sulfinimidinates of the type Li[RS(NR )2] A. The lithium derivatives may be hydrolysed by water to R NS(R)NHR which, upon treatment with MH (M=Na, K) or the metal (M=Rb, Cs) in THF, produces the heavier alkali-metal derivatives.132 The structures of these complexes are influenced by (a) the size and electronic properties of the R group, (b) the size of the alkali metal cation, and (c) solvation of the alkali-metal cation. 

Li[Ph4P2N4S2R].274 Alkali-metal derivatives of the dianion [Ph4P2N4S2]2 are prepared by treatment of 111 (E=S, R=Ph) with alkali-metal superhydrides M[Et3BH] (M=Li, Na].275 The methylene bridge between the two sulfur atoms in 116 is introduced by the addition of diiodomethane to... 

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