Vinylation and polymerization with trivinylaluminum. I. Vinylation of organic halides as a model for termination in cationic polymerization leading to vinyl end groups

Abstract

AbstractAn improved synthesis of trivinylaluminum (V3Al) is described. The proton magnetic resonance (PMR) spectrum of V3Al was recorded and analyzed. A new vinylation method involving the use of V3Al as the vinylating agent has been developed, and the vinylation of organic halides by V3Al was studied at −30, −50 and −70°C. Primary alkyl chlorides, such as methyl and methylene chloride, do not react with V3Al and were used as solvents. Secondary chlorides such as 2‐chloropropane also do not react. t‐Butyl chloride gives rise to t‐butylethylene (70–98%), depending on reaction conditions, and the allylic chlorides, 3‐chloro‐1‐butene, and 3‐chloro‐3‐methyl‐1‐butene, yield the expected vinylated products and their isomers (∼90%). Allyl and benzyl chloride do not react under the conditions tried. The reaction between V3Al and the ditertiary dichloride 2,6‐dichloro‐2,6‐dimethylheptane yields several isomeric C13H24 and C11H20 hydrocarbons; however, surprisingly, C9H16 does not form. The C13 hydrocarbons arise by divinylation at the termini of the dichloride, while the C11 hydrocarbons are formed by vinylation at one and proton elimination at the other terminus of the dichloride. The presence of unsaturated C13H24 and C11H20 isomers is most likely due to proton induced isomerization. These results are explained by a proximity effect involving vinylation at one end of the dichloride by V3Al followed by rapid reaction of the second chlorine (mostly) by V2AlCl generated in situ during the first vinylation in the proximity of the chloride. At the other chlorine terminus V2AlCl causes either a second vinylation (leading to C13 hydrocarbons) or a proton elimination (leading to C11 hydrocarbons). The absence of C9H16 among the reaction products indicates that V3Al exclusively effects vinylation. The RCl + V3Al ← RV + V2AlCl reaction may be regarded as a model for initiation followed by immediate termination in cationic olefin polymerization, a process leading to vinyl‐ended polymers.