Kinetics of reaction of metal alkyls with alkenes. Part 8.—Oligomerization of ethylene by n-butyl-lithium-NNN′N′-tetramethylethylenediamine

Abstract

n-Butyl-lithium (BuLi) in the presence of NNN′N′-tetramethylethylenediamine (TMEDA) progressively adds on ethylene molecules to produce a linear alkyl-lithium compound. This oligomerization has been studied at low pressure, 0–2 atmosphere, and temperature, 270–310 K, and hydrocarbons, up to C₁₅₀, have been isolated on hydrolysis. The rate of consumption of ethylene depends on the pressure and BuLi concentration but is independent of TMEDA concentration. No addition of ethylene, however, occurs in the absence of TMEDA or in the presence of simple tertiary amines under the conditions used. The molecular weights of the hydrolyzed reaction products increase with the mol of ethylene consumed and their distributions (M_w/M_n) are Poisson, indicating the absence of any transfer or termination steps. A mechanism for the addition reaction is proposed.