Effect of organic additives having functional groups in olefin metathesis

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The dependence of product yields on the amount of various organic additives containing heteroatom functional groups was investigated for the metathesis of 2-heptene in benzene at room temperature catalyzed by WCl 6SnBu 4 (1:1). Without additives, heptylbenzenes were major products, and 5-decene and 2-butene were minor ones. With increasing amounts of ethers, ketones, sulfides, pyridine, amines, a cyanide, an amide, a sulfoxide, a tertiary phosphine, and alcohols, the yield of 5-decene first increased markedly and that of heptylbenzene decreased; thereafter, the yield of 5-decene was also lowered. When reaction temperatures were elevated to 80 or 120 °C, the amount of the additives needed to inhibit metathesis increased. In particular, for ether and ester addition significant metathesis was observed even at an additive/catalyst ratio of 30. This suggests that the metathesis of unsaturated ethers and esters proceeds rather efficiently. A comparison of the relative ability of these additives to inhibit metathesis and alkylation shows that the active species in the former reaction are softer acids than those of the latter. It was shown that additives raise metathesis yields mainly by protecting the active species of metathesis from decay, although the inhibition of the alkylation may also have some effect on the yields. The decay of metathesis species takes place easily in a medium where the alkylation proceeds well.