Organoalkalis reactions with

There are three general types of metallation reactions (metal-hydrogen exchange) that are commonly used to synthesize organoalkali metal compoimds from organic molecules Direct reaction with an alkali metal, reaction with an alkali metal hydride, or reaction with an organo- or amido-alkali metal. Since these reactions involve acid/base equilibria, they are dependent on both the C-H acidity of the organic molecule and the basicity of the alkali metal source. 

For example, n-pentylsodium may be prepared in 80-90% yield by reaction between Na sand (25 jxra particle size) and 1-chloropentane in n-pentane at — 10°C in a creased flask equipped with a high-speed stirrer. Comparable 3delds of n-pentylsodium may be obtained in n-heptane, in which the yield of organoalkali decreases only from 85 to 75% after storage at RT for 24 days. In contrast, in n-BujO the yield of n-pentylsodium is 63%, but after 10 days most of the reagent has decomposed by reaction with the solvent. In 1,2-dimethoxyethane (DME) and 12 the yields of n-pentylsodium are < 15 %. Even under inert solvents samples of n-pentylsodium must be prepared and stored at RT or lower because pyrolysis is appreciable at 50°C and rapid at 100°C. 

The preparation of adducts of conjugated hydrocarbons by reaction with alkali metals demands absence of Oj, HjO or solvent impurities that can combine with the organometallic product or the alkali metal. The T must be below the decomposition point of the organoalkali compound in the particular solvent. Adequate contact between the alkali metal and the hydrocarbon must be established. In small-scale preparations the alkali metal is deposited as a mirror on the walls of the reaction vessel, where it can come in contact with solvent. In larger scale or synthetic preparations the alkali metal is in the form of a sand or dispersion (see 5.5.3.2.1), and good stirring may be helpful. 

The presence of the two amido protons in 3 also provides the opportunity to generate heterobimetallic clusters by reaction with organoalkali reagents. The magnesiated cubane 53 is produced in 69% yield from the reaction of dibutylmagnesium with 3 in hot THF. The reaction of 3 with two equivalents of butyllithium at -78 °C in THF generates 54 in 39% yield. The structure of the solvent-separated ion pair 54 is analogous to that of 41. 

Reaction of Organoalkali Compounds with Carbon Disulfide... 

The reaction of sp3 organoalkali compounds with carbon disulfide usually does not stop at the stage of the initial adduct, but is followed by an extremely fast conversion of the dithiocarboxylate into a geminal ene-dithiolate ... 

Reactions of Organoalkali Compounds with Halogenating Agents... 

Reactions of organoalkali compounds with disulfides and trialkylchlorosilane are often extremely fast. The usual procedure involves addition of the reagents to a... 

The process may be complicated, however, by reaction of intermediates I and II with unreacted phosphorus to gi e more complex phosphides which in turn arc broken down by the organometallic reactant. Ileac-tions of organoalkali compounds with phosphorus may also proceed tlirougli such intermediates, but the greater reactivity of the alkali derivatives evidently permits further phosphorus-phosphorus bond cleavage leading to more complex ions. 

In another study (SO) l-chloro-2-p-biphenylylethane-l,l-d2 was allowed to react with various alkali metals in tetrahydrofuran (organoalkali compounds appear to have longer lifetimes in tetrahydrofuran than in 1,2-dimethoxyethane). Reaction with lithium at -70°C gave a good yield of 2-/7-biphenylyllithium-l,l-d2 (35) however on warming to Ot this... 

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