Comparative Dimerization of 1‐Butene with a Variety of Metal Catalysts, and the Investigation of a New Catalyst for C-H Bond Activation

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Abstract
Catalytic dimerization of 1‐butene by a variety of catalysts is carried out, and the products are analyzed by gas chromatography and mass spectrometry. Catalysts based on cobalt and iron can produce highly linear dimers, with the cobalt‐based dimers exceeding 97 % linearity. Catalysts based on vanadium and aluminum prefer to make branched dimers, which are most often methyl‐heptenes in the case of vanadium and almost exclusively 2‐ethyl‐1‐butene in the case of aluminum. The vanadium catalyst also produces substantial amounts of dienes and alkanes, suggesting a competing hydrogenation/dehydrogenation pathway that appears to involve vinyl CH bond activation. Nickel catalysts are generally less selective than those based on iron or cobalt for making linear dimers, but they can make dimers with 60 % linearity. The major by‐products for the nickel systems are trisubstituted internal olefins. An important side reaction that must be considered for dimerization reactions is 1‐butene isomerization to 2‐butene, which makes recycling the butene difficult for a linear dimerization process. Aluminum, iron, and vanadium systems promote very little isomerization, but nickel and cobalt systems tend to isomerize the undimerized substrate heavily.