Organolithium chelates

Some Mechanistic Aspects of N-Chelated Organolithium Catalysis... 

In 1962 and 1963 the chelated organolithium complexes and their application in ethylene telomerization were discovered independently of each other by Eberhardt (12) at Sun Oil Co. This research led to two patents (13, 14) in which the claims involving chelated catalysts were... 

Many chelated organolithium compounds can be obtained as 1 1 complexes, but only certain lithium aggregates appear to form insoluble... 

Because of the exceptional reactivity and chemical importance of the amine-chelated organolithium reagents, their stereochemical properties are of special significance. Our interest centered on six points ... 

The position of the lithium atom in N-chelated organolithium compounds, (TMEDLi)2R, also cannot be predicted from electrostatic con-... 

In short the chemistry and properties of the inorganic lithium chelates should promote their uses in many applications. This is the case for the N-chelated organolithium reagents, as evidenced by the frequency of appearance of these systems in the literature. We hope that the poly-amine-purification technique presented here will improve the availability of useful chelating ligands and stimulate additional research in this area. 

Conjugated Dienes and Other Monomers. Alkyllithiums such as n-butyllithium—and even the growing polyethylene carbon-lithium bond complexed with chelating diamines such as TMEDA—are effective initiators for the polymerization of conjugated dienes such as 1,3-butadiene and isoprene. A polybutadiene of high 1,2-content can be produced from butadiene in hydrocarbon solvents using these N-chelated organolithium catalysts. 

Chelated Organolithium Catalyst. To 1.6 ml of 1.6N n-butyllithium in hexane were added 50 ml toluene and 0.6 ml PMDT, generating PMDT-BzLi in situ. The reaction was kept at 40°C while butadiene was introduced into the atmosphere above the reaction (22 cc/min) for 2 hrs. The reaction was then quenched with 5 ml of water. The organic layer was separated, dried (K2C03), and the solvent was removed under vacuum to give 5 grams of product having Mn — 2549. 

Telomerization of Benzene and Butadiene. To 0.26 gram (2.63 mmoles) of phenylsodium were added 50 ml of benzene and 0.7 ml of iso-HMTT. The reaction was kept at 70°C while butadiene was introduced into the atmosphere above the reaction for 2 hrs at 22 cc/min. A work-up similar to that given under chelated organolithium catalyst gave 7 grams of benzenebutadiene telomer with Mn = 998. 

Much of the early work with N-chelated organolithium compounds was concerned with polymeric reactions—in particular the telomerization of ethylene onto aromatic hydrocarbons such as benzene and toluene to produce long-chain alkylbenzenes (6,7, 8, 9). 

Our interest in the synthetic utility of N-chelated organolithium compounds was prompted by this early work. Since detailed experimental procedures were not generally available at that time, we initiated a study of the effects of time, temperature, stoichiometry, etc., on the reactions of BuLi-TMEDA with benzene. We found that optimum metalation of benzene occurs when the preformed BuLi-TEMEDA complex, prepared from equimolar amounts of the organolithium reagent and diamine, is... 

Metalations of various organometallic ir complexes with N-chelated organolithium complexes have also received considerable attention in recent years. Perhaps the best known organometallic tr complex is ferrocene. Although it was discovered very early in the development of fer-... 

All the above reactions involve hydrogen—lithium interconversion (metalation). There are a limited amount of data available indicating that N-chelated organolithium intermediates also undergo nucleophilic addition to carbon-carbon double and triple bonds much more readily than does the organolithium reagent alone. Indeed, this enhanced reactivity toward addition reactions is a key factor in the telomerization of ethylene onto aromatic hydrocarbons (6, 7,8,9). 

In addition, the organoalkali initiators only work effectively with the conjugated monomers. They are ineffective with the olefins, or even with ethylene. (Some success has been reported (A8) in the polymerization of ethylene to a reasonably high molecular weight in highly chelated organolithium systems. However, these polymerizations required relatively higher temperatures and showed much evidence of termination reactions.)... 

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