{"id":8048,"date":"2012-10-17T16:59:09","date_gmt":"2012-10-17T15:59:09","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=8048"},"modified":"2013-03-08T17:11:14","modified_gmt":"2013-03-08T17:11:14","slug":"trimethylenemethane-ruthenium-benzene","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8048","title":{"rendered":"Trimethylenemethane Ruthenium benzene"},"content":{"rendered":"
\n

Every once in a while, one encounters a molecule which instantly makes an interesting point. Thus Ruthenium is ten electrons short of completing an 18-electron shell<\/a>, and it can form a complex with benzene on one face and a ligand known as trimethylenemethane<\/strong><\/em> on the other[1]<\/a><\/span>.<\/p>\n

\"\"<\/p>\n

This four-carbon molecule has been known for a long time[2]<\/a><\/span> as a highly reactive intermediate, and as with cyclobutadiene (another 4\u03c0-electron species), it can be greatly stabilised (and crystallised) by coordination to a metal. Some twenty examples are known, and one is shown below.<\/p>\n

\"\"

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

Why might it be interesting? Because the trimethylenemethane has four carbons, of which the closest to the metal is the central one (2.03\u00c5). The three outer distances are longer at 2.19\u00c5. If one were to (formally) draw a bond from the metal to the central carbon atom, that atom would become what is known as hemispherical, i.e. all four ligands would be contained in a single hemisphere. This molecule is however normally represented with bonds only to the peripheral carbons, and with no bond<\/a> to what is after all the shortest of the four distances!\u00a0<\/p>\n

A QTAIM analysis<\/a> gives the same answer. Only three bond-critical points are found in the topology of the electron density (red), and at the centre where one might have expected a Ru-C bond, one finds in fact a cage-critical point (blue). Of course, another way of looking at the molecule is that the trimethylenemethane simply contributes four electrons to the valence shell of the metal without trying to partition these into bonds. These four electrons, together with six from the benzene ligand, complete the 18-electron ruthenium shell.<\/p>\n

\"\"<\/p>\n

So the take home message is that whilst the concept of discrete two-centre bonds still has its uses, this little molecule reminds us that bonds can be slippery customers. The common practice in most computer codes that represent molecules, of joining up the shortest contacts to form “bonds”, would lead us in this instance to hemispherical carbon. The consensus seems to be that this molecule does not exhibit this.<\/p>\n

\n

POSTSCRIPT: <\/strong>\u00a0An \u00a0ELF analysis of the related Iron\u00a0complex<\/a> is shown below. It too shows three disynaptic basins for the three peripheral \u00a0C-Fe “bonds” (red arrows), and none for the central one. The total basin integration for these three is \u00a04.82e, a bit more than the nominal \u00a04-electron ability of the ligand.\u00a0<\/p>\n

\"\"

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

References<\/h2>\n
  1. G.E. Herberich, and T.P. Spaniol, \"Trimethylenemethane complexes of ruthenium via the trimethylenemethane dianion\", Journal of the Chemical Society, Chemical Communications<\/i>, pp. 1457, 1991. https:\/\/doi.org\/10.1039\/c39910001457<\/a>\n\n<\/li>\n
  2. P. Dowd, \"Trimethylenemethane\", Accounts of Chemical Research<\/i>, vol. 5, pp. 242-248, 1972. https:\/\/doi.org\/10.1021\/ar50055a003<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    Every once in a while, one encounters a molecule which instantly makes an interesting point. Thus Ruthenium is ten electrons short of completing an 18-electron shell, and it can form a complex with benzene on one face and a ligand known as trimethylenemethane on the other. This four-carbon molecule has been known for a long […]<\/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,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[4],"tags":[925,157,317],"ppma_author":[2661],"class_list":["post-8048","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-iron-complex","tag-metal","tag-postscript"],"yoast_head":"\nTrimethylenemethane Ruthenium benzene - Henry Rzepa's Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8048\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Trimethylenemethane Ruthenium benzene - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"Every once in a while, one encounters a molecule which instantly makes an interesting point. 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An \"inverted\" sandwich is where the carbon\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":275,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=275","url_meta":{"origin":8048,"position":1},"title":"A molecule with an identity crisis: Aromatic or anti-aromatic?","author":"Henry Rzepa","date":"April 13, 2009","format":false,"excerpt":"In 1988, Wilke reported molecule 1 It was a highly unexpected outcome of a nickel-catalyzed reaction and was described as a 24-annulene with an unusual 3D shape. Little attention has been paid to this molecule since its original report, but the focus has now returned! 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It was cyclo-octatetraene or (CH)8, and it was made by Willst\u00e4tter and Waser to try to find out if benzene,\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2010\/05\/metallatrefoil.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":11450,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=11450","url_meta":{"origin":8048,"position":3},"title":"The NMR spectra of methano[10]annulene and its dianion. The diatropic\/paratropic inversion.","author":"Henry Rzepa","date":"October 26, 2013","format":false,"excerpt":"The 1H NMR spectrum of an aromatic molecule such as benzene is iconic; one learns that the unusual chemical shift of the protons (~\u03b4 7-8 ppm) is due to their deshielding by a diatropic ring current resulting from the circulation of six aromatic \u03c0-electrons following the H\u00fcckel 4n+2 rule. 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The one on\u2026","rel":"","context":"In "Interesting chemistry"","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2019\/10\/b3-1423-B2u-1024x575.gif?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8048","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8048"}],"version-history":[{"count":17,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8048\/revisions"}],"predecessor-version":[{"id":8064,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8048\/revisions\/8064"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8048"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8048"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8048"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=8048"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}