{"id":22971,"date":"2020-11-07T12:13:33","date_gmt":"2020-11-07T12:13:33","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=22971"},"modified":"2020-11-07T12:13:33","modified_gmt":"2020-11-07T12:13:33","slug":"a-new-example-of-a-quadruple-bond-from-carbon-to-fe","status":"publish","type":"post","link":"https:\/\/rzepa.net\/blog\/2020\/11\/07\/a-new-example-of-a-quadruple-bond-from-carbon-to-fe\/","title":{"rendered":"A new example of a quadruple bond from carbon – to Fe."},"content":{"rendered":"

Way back in 2010, I was writing<\/a> about an experience I had just had during an organic chemistry tutorial, which morphed into speculation as to whether a carbon atom might sustain a quadruple bond to nitrogen. A decade on, and possibly approaching 100 articles by many authors on the topic, quadruple bonds to carbon continue to fascinate. Now an article as appeared[cite]10.1039\/d0cp03436c[\/cite] repeating this speculation for a carbon to iron quadruple bond,‡<\/sup> in the very simple species C\u2a78Fe(CO)3<\/sub> (see also a Rh-B equivalent[cite]10.1021\/acs.jpclett.9b03484[\/cite]). This is particularly exciting because of the very real prospect of synthesising this species and perchance getting a crystal structure (something not possible with most of the other quadruply bonded carbon systems studied to date).<\/p>\n

They authors report[cite]10.1039\/d0cp03436c[\/cite] that this sytem is well described by a single-configurational wavefunction and hence that a M062X\/Def2-TZVPP calculation is a good description of the bonding. In the article you will find the valence molecular orbitals shown, which by their nature show a lot of delocalisation. Because the more localised NBOs are not shown in the article, I illustrate them here, as 3D rotatable models. The DOI for the calculation can be found at\u00a010.14469\/hpc\/7537<\/a>.<\/p>\n\n\n\n\n\n\n\n
CFe(CO)3<\/sub><\/th>\n<\/tr>\n
NBO 37 π<\/th>\nNBO 36 π<\/th>\n<\/tr>\n
\n
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Click to view 3D model of NBO 37<\/figcaption><\/figure>\n<\/td>\n
\n
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Click to view 3D model of NBO 36<\/figcaption><\/figure>\n<\/td>\n<\/tr>\n
NBO 33 σ<\/th>\nNBO 23 σ<\/th>\n<\/tr>\n
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Click to view 3D model of NBO 33<\/figcaption><\/figure>\n<\/td>\n
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Click to view 3D model of NBO 23<\/figcaption><\/figure>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

These NBOs show very clearly that the two higher energy orbitals are orthogonal \u03c0-bonds to carbon from Fe and the two lower energy orbitals are both \u03c3-bonds to carbon from Fe. Exactly the same picture appears for C2<\/sub>, which has been often mentioned<\/a> on this blog.<\/p>\n

All that remains is that some inspired synthetic chemist sets out to make C\u2a78Fe(CO)3<\/sub> and to report back on its properties. I fancy the last has not yet been heard about quadruple bonds to carbon!<\/p>\n

\n

Postscript:<\/b> Here are the analogous orbitals for the species N\u2a78Mn(CO)3<\/sub> to illustrate their evolution across an isoelectronic series.<\/p>\n\n\n\n\n\n\n\n
NMn(CO)3<\/sub><\/th>\n<\/tr>\n
NBO 35<\/th>\nNBO 34<\/th>\n<\/tr>\n
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Click to view 3D model of NBO 35<\/figcaption><\/figure>\n<\/td>\n
\n
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Click to view 3D model of NBO 34<\/figcaption><\/figure>\n<\/td>\n<\/tr>\n
NBO 33<\/th>\nNBO 20<\/th>\n<\/tr>\n
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Click to view 3D model of NBO 33<\/figcaption><\/figure>\n<\/td>\n
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Click to view 3D model of NBO 20<\/figcaption><\/figure>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

NBO 33 (the higher in energy of the two σ-type bonds) has an interesting structure. Here it is at a slightly lower threshold:<\/p>\n

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Click to view 3D model of NBO 33 for NMn(CO)3 at threshold 0.015au<\/figcaption><\/figure>\n

It has an inner compact σ-bond running along the axis of the bond and an outer “wrap” of different phase. A two layer σ-bond if you like!<\/p>\n

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‡<\/sup>This was one of the shortlisted candidates for Molecule of the Year, 2020.<\/a> See also[cite]10.1039\/D1CP00598G[\/cite]<\/p>\n","protected":false},"excerpt":{"rendered":"

Way back in 2010, I was writing about an experience I had just had during an organic chemistry tutorial, which morphed into speculation as to whether a carbon atom might sustain a quadruple bond to nitrogen. A decade on, and possibly approaching 100 articles by many authors on the topic, quadruple bonds to carbon continue […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-22971","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry"],"_links":{"self":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/22971","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/comments?post=22971"}],"version-history":[{"count":0,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/posts\/22971\/revisions"}],"wp:attachment":[{"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/media?parent=22971"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/categories?post=22971"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rzepa.net\/blog\/wp-json\/wp\/v2\/tags?post=22971"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}