{"id":13174,"date":"2014-12-14T08:07:50","date_gmt":"2014-12-14T08:07:50","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=13174"},"modified":"2014-12-14T08:07:50","modified_gmt":"2014-12-14T08:07:50","slug":"cyclopropanation-the-mechanism-of-the-simmons-smith-reaction","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=13174","title":{"rendered":"Cyclopropanation: the mechanism of the Simmons\u2013Smith reaction."},"content":{"rendered":"
\n

These posts contain the computed potential energy surfaces for a fair few “text-book” reactions. Here I chart the course of the cyclopropanation of alkenes using the Simmons-Smith reagent,[1]<\/a><\/span> as\u00a0prepared from di-iodomethane using zinc metal insertion into a C-I bond.
\n\"simmonds-smith\"<\/a><\/p>\n

Two reactions it can be compared with are the epoxidation of ethene <\/a>using a peracid and dichlorocyclopropanation<\/a>. The latter is a four-electron pericyclic process, which is thermally forbidden. The outcome there is that the two new bonds form very asynchronously to avoid transition state antiaromaticity<\/a>. The former is a more complex reaction, best described as a six-electron process\u00a0which allows both C…O bonds to form at the same rate. So which of these two does the\u00a0Simmons\u2013Smith mechanism correspond to?<\/p>\n

The calculation as undertaken at a \u03c9B97XD\/Def2-TZVPD-PP (solvent=dichloromethane) level[2]<\/a><\/span> shows the two C…C bonds forming at more or less the same rate. The reaction therefore resembles epoxidation rather than dichlorocyclopropanation.<\/p>\n

\"SS\"<\/a><\/p>\n

The\u00a0intrinsic reaction coordinate (IRC)[3]<\/a><\/span> is shown below, revealing a concerted and almost synchronous reaction. The synchronicity is all the more surprising given the diversity of bonds forming\/breaking.
\n\"SSa\"<\/a>
\n\"SSE\"<\/a><\/p>\n

\"SSG\"<\/a><\/p>\n

There are slight and tantalizing hints that the alkene and the I-Zn-CH2<\/sub>-I components initially form a weak \u03c0-complex, which then rearranges into the TS, and then again a weak complex at the end. The NCI surfaces for both are shown below, and show clear signs of dispersion-like stabilisations for both of them!\u00a0The strange torus around the Zn-I bond is due to the need for a lower density threshold to filter out the covalent interactions.<\/p>\n

\"Click

Click for 3D<\/p><\/div>\n

\"Click

Click for 3D<\/p><\/div>\n

References<\/h2>\n
  1. H.E. Simmons, and R.D. Smith, \"A NEW SYNTHESIS OF CYCLOPROPANES FROM OLEFINS\", Journal of the American Chemical Society<\/i>, vol. 80, pp. 5323-5324, 1958. https:\/\/doi.org\/10.1021\/ja01552a080<\/a>\n\n<\/li>\n
  2. H.S. Rzepa, \"C 3 H 6 I 2 Zn 1\", 2014. https:\/\/doi.org\/10.14469\/ch\/147617<\/a>\n\n<\/li>\n
  3. H.S. Rzepa, \"Gaussian Job Archive for C3H6I2Zn\", 2014. https:\/\/doi.org\/10.6084\/m9.figshare.1270441<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    These posts contain the computed potential energy surfaces for a fair few “text-book” reactions. Here I chart the course of the cyclopropanation of alkenes using the Simmons-Smith reagent, as\u00a0prepared from di-iodomethane using zinc metal insertion into a C-I bond. Two reactions it can be compared with are the epoxidation of ethene using a peracid and […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1085],"tags":[1226,1236,1294],"class_list":["post-13174","post","type-post","status-publish","format-standard","hentry","category-reaction-mechanism-2","tag-computed-potential-energy-surfaces","tag-di-iodomethane-using-zinc-metal-insertion","tag-simmons"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-3qu","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/13174","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=13174"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/13174\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=13174"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=13174"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=13174"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}