{"id":16819,"date":"2016-09-19T11:02:37","date_gmt":"2016-09-19T10:02:37","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=16819"},"modified":"2016-09-19T11:12:27","modified_gmt":"2016-09-19T10:12:27","slug":"whats-in-a-name-stabilised-nitrenes","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16819","title":{"rendered":"What\u2019s in a name? Stabilised “nitrenes”."},"content":{"rendered":"
\n

I previously explored<\/a> stabilized “carbenes” with the formal structures (R2<\/sub>N)2<\/sub>C:, concluding that perhaps the alternative ionic representation R2<\/sub>N+<\/sup>=C–<\/sup>NR2<\/sub>\u00a0might reflect their structures better. Here I take a broader look at the “carbene” landscape before asking the question “what about nitrenes?”<\/p>\n

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

The top row shows the compounds for which no crystal structure could be found.\u2021<\/sup> This includes the traditional carbon-substituted unstabilized carbenes, as well as those substituted with either group 4A or 6A elements (Si, S, etc). Isolated hits were<\/strong>\u00a0however found as follows for other combinations (all interesting, but I do not discuss them here).<\/p>\n

    \n
  1. R2<\/sub>N-C-CR3\u00a0<\/sub>[1]<\/a><\/span>,[2]<\/a><\/span>,[3]<\/a><\/span>,[4]<\/a><\/span>,[5]<\/a><\/span>,[6]<\/a><\/span><\/li>\n
  2. R2<\/sub>P-C-Si [7]<\/a><\/span>,[8]<\/a><\/span><\/li>\n
  3. R2<\/sub>P-C-PR2<\/sub> [9]<\/a><\/span>,[10]<\/a><\/span><\/li>\n
  4. R2<\/sub>N-C-OR [11]<\/a><\/span><\/li>\n
  5. R2<\/sub>N-C-SR [12]<\/a><\/span><\/li>\n<\/ol>\n

    At this point I turned to nitrenes<\/a>. As with unstabilised carbenes, the nitrogen is\u00a0described as having one covalent bond, one unshared spin-paired lone pair of electrons and two further unpaired electrons to give a total valence shell count of six (and in fact a triplet spin state). Are there any examples? Just one, formally corresponding to\u00a0R2<\/sub>P-N (DEGSEP[13]<\/a><\/span>). To explore what the nature of the single P-N bond is, I did a search for the P-N bond lengths of all P-N compounds in the CSD (of any bond type). The distribution shows ~1.48\u00c5 as the shortest and ~1.8\u00c5 as the longest.There is no sign of a multimodal distribution indicating partitioning into e.g.<\/em> single, double or triple bonds.<\/p>\n

    \"p-n-distances\"<\/p>\n

    So what about our nitrene? The P-N bond is 1.456\u00c5, which is very much at the short end of the spectrum above, and so pretty far from the formal simple definition of a nitrene given above. So now for a\u00a0\u03c9B97XD\/Def2-TZVPP calculation of the singlet wavefunction[14]<\/a><\/span> (the triplet state is 22 kcal\/mol higher in energy[15]<\/a><\/span>) for a model compound with calculated CN distance 1.493\u00c5 and from which an ELF-based localisation and integration of the electron basins can be derived. The total basin integration for the N can be taken as 7.77e (close to the octet) if basins 15 and 16 are assumed to be shared (covalent) and this gives the P-N bond double bond character. If basins 15 and 16 are not included (and taken as localised just on the P), the N has 5.81e and an associated single bond.\u00a0<\/p>\n

    \"nitrene1\"<\/p>\n

    A search of the CSD specifying P\u2261N as the search query returns lengths in the range 1.47-1.56\u00c5, which our example certainly conforms to. So perhaps we can tentatively conclude that the only example thus far reported of a crystalline nitrene in fact sustains a very short bond to the nitrogen. It could be considered as the N having a filled octet in its valence shell, and certainly a bond order higher than one, if not actually triple.<\/p>\n

    \n

    \u2021<\/sup>For the search query, see [16]<\/a><\/span><\/p>\n

    References<\/h2>\n
    1. Marchenko, Anatoliy., Koidan, Heorgyi., Hurieva, Anastasiya., Kurpiieva, Olena., Vlasenko, Yurii., Kostyuk, Aleksandr., Tubaro, Cristina., Lenarda, Anna., Biffis, Andrea., and Graiff, Claudia., \"CCDC 997216: Experimental Crystal Structure Determination\", 2014. https:\/\/doi.org\/10.5517\/cc12gp8h<\/a>\n\n<\/li>\n
    2. A. Marchenko, H. Koidan, A. Hurieva, O. Kurpiieva, Y. Vlasenko, A. Kostyuk, C. Tubaro, A. Lenarda, A. Biffis, and C. Graiff, \"N-phosphanyl-imidazolin-2-ylidenes: Novel stable carbenes as bidentate ligands for late transition metals\", Journal of Organometallic Chemistry<\/i>, vol. 771, pp. 14-23, 2014. https:\/\/doi.org\/10.1016\/j.jorganchem.2014.05.036<\/a>\n\n<\/li>\n
    3. Lavallo, V.., Mafhouz, J.., Canac, Y.., Donnadieu, B.., Schoeller, W.W.., and Bertrand, G.., \"CCDC 236934: Experimental Crystal Structure Determination\", 2004. https:\/\/doi.org\/10.5517\/cc7yk1r<\/a>\n\n<\/li>\n
    4. V. Lavallo, J. Mafhouz, Y. Canac, B. Donnadieu, W.W. Schoeller, and G. Bertrand, \"Synthesis, Reactivity, and Ligand Properties of a Stable Alkyl Carbene\", Journal of the American Chemical Society<\/i>, vol. 126, pp. 8670-8671, 2004. https:\/\/doi.org\/10.1021\/ja047503f<\/a>\n\n<\/li>\n
    5. Lavallo, V.., Frey, G.D.., Kousar, S.., Donnadieu, B.., and Bertrand, G.., \"CCDC 651272: Experimental Crystal Structure Determination\", 2008. https:\/\/doi.org\/10.5517\/ccpvpsz<\/a>\n\n<\/li>\n
    6. V. Lavallo, G.D. Frey, S. Kousar, B. Donnadieu, and G. Bertrand, \"Allene formation by gold catalyzed cross-coupling of masked carbenes and vinylidenes\", Proceedings of the National Academy of Sciences<\/i>, vol. 104, pp. 13569-13573, 2007. https:\/\/doi.org\/10.1073\/pnas.0705809104<\/a>\n\n<\/li>\n
    7. Marsh, R.E.., and Clemente, D.A.., \"CCDC 625624: Experimental Crystal Structure Determination\", 2008. https:\/\/doi.org\/10.5517\/ccp00f3<\/a>\n\n<\/li>\n
    8. R.E. Marsh, and D.A. Clemente, \"A survey of crystal structures published in the Journal of the American Chemical Society\", Inorganica Chimica Acta<\/i>, vol. 360, pp. 4017-4024, 2007. https:\/\/doi.org\/10.1016\/j.ica.2007.02.050<\/a>\n\n<\/li>\n
    9. Martin, D.., Baceiredo, A.., Gornitzka, H.., Schoeller, W.W.., and Bertrand, G.., \"CCDC 252551: Experimental Crystal Structure Determination\", 2005. https:\/\/doi.org\/10.5517\/cc8gst9<\/a>\n\n<\/li>\n
    10. D. Martin, A. Baceiredo, H. Gornitzka, W.W. Schoeller, and G. Bertrand, \"A Stable P\u2010Heterocyclic Carbene\", Angewandte Chemie International Edition<\/i>, vol. 44, pp. 1700-1703, 2005. https:\/\/doi.org\/10.1002\/anie.200462239<\/a>\n\n<\/li>\n
    11. R.W. Alder, C.P. Butts, and A.G. Orpen, \"Stable Aminooxy- and Aminothiocarbenes\", Journal of the American Chemical Society<\/i>, vol. 120, pp. 11526-11527, 1998. https:\/\/doi.org\/10.1021\/ja9819312<\/a>\n\n<\/li>\n
    12. A.J. Arduengo, J.R. Goerlich, and W.J. Marshall, \"A Stable Thiazol\u20102\u2010ylidene and Its Dimer\", Liebigs Annalen<\/i>, vol. 1997, pp. 365-374, 1997. https:\/\/doi.org\/10.1002\/jlac.199719970213<\/a>\n\n<\/li>\n
    13. Dielmann, F.., Back, O.., Henry-Ellinger, M.., Jerabek, P.., Frenking, G.., and Bertrand, G.., \"CCDC 884586: Experimental Crystal Structure Determination\", 2013. https:\/\/doi.org\/10.5517\/ccyph14<\/a>\n\n<\/li>\n
    14. H. Rzepa, \"DEGSEP\", 2016. https:\/\/doi.org\/10.14469\/hpc\/1625<\/a>\n\n<\/li>\n
    15. H. Rzepa, \"DEGSEP triplet\", 2016. https:\/\/doi.org\/10.14469\/hpc\/1626<\/a>\n\n<\/li>\n
    16. H. Rzepa, \"CSD Search query for carbenes\", 2016. https:\/\/doi.org\/10.14469\/hpc\/1624<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

      I previously explored stabilized “carbenes” with the formal structures (R2N)2C:, concluding that perhaps the alternative ionic representation R2N+=C–NR2\u00a0might reflect their structures better. Here I take a broader look at the “carbene” landscape before asking the question “what about nitrenes?” The top row shows the compounds for which no crystal structure could be found.\u2021 This includes […]<\/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":true,"_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":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[1745],"tags":[],"ppma_author":[2661],"class_list":["post-16819","post","type-post","status-publish","format-standard","hentry","category-crystal_structure_mining"],"yoast_head":"\nWhat\u2019s in a name? 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Carbenes: a reality check.","author":"Henry Rzepa","date":"September 11, 2016","format":false,"excerpt":"To quote from Wikipedia: in chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The most ubiquitous type of carbene of recent times is the one shown below as 1, often referred to as a resonance stabilised or\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":14037,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=14037","url_meta":{"origin":16819,"position":1},"title":"R-X\u2261X-R: G. N. Lewis’ 100 year old idea.","author":"Henry Rzepa","date":"May 22, 2015","format":false,"excerpt":"As I have noted elsewhere, Gilbert N. Lewis wrote a famous paper entitled \"the atom and the molecule\", the centenary of which is coming up. In a short and rarely commented\u00a0upon remark, he speculates about the shared electron pair structure of acetylene,\u00a0\u00a0R-X\u2261X-R (R=H, X=C). It could, he suggests, take up\u2026","rel":"","context":"In "Chemical IT"","block_context":{"text":"Chemical IT","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":29383,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29383","url_meta":{"origin":16819,"position":2},"title":"The mysterious N=N double bond in nitrosobenzene dimer.","author":"Henry Rzepa","date":"August 11, 2025","format":false,"excerpt":"In an earlier blog, I discussed the curly arrows associated with the known dimerisation of nitrosobenzene, and how the\u00a0N=N double bond (shown in red below) forms in a single concerted process. One of the properties of this molecule is that the equilibrium between the monomer and dimer can be detected,\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":16361,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16361","url_meta":{"origin":16819,"position":3},"title":"What is the approach trajectory of enhanced (super?) nucleophiles towards a carbonyl group?","author":"Henry Rzepa","date":"May 11, 2016","format":false,"excerpt":"I have previously commented on the B\u00fcrgi\u2013Dunitz angle, this being the preferred approach trajectory of a nucleophile towards the electrophilic carbon of a carbonyl group. Some special types of nucleophile such as hydrazines (R2N-NR2) are supposed to have enhanced reactivity due to what might be described as\u00a0buttressing of adjacent lone\u2026","rel":"","context":"In "Chemical IT"","block_context":{"text":"Chemical IT","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=2"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":29410,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29410","url_meta":{"origin":16819,"position":4},"title":"Energy decomposition analysis of hindered alkenes: Tetra t-butylethene and others.","author":"Henry Rzepa","date":"August 13, 2025","format":false,"excerpt":"In the previous post, I introduced the N=N double bond in nitrosobenzene dimer, arguing that even though it was a formal double bond, its bond dissociation energy made it nonetheless a very weak double bond! This was backed up by a technique known as energy decomposition analysis or EDA. Here\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":9360,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9360","url_meta":{"origin":16819,"position":5},"title":"\u03c3-\u03c0-Conjugation: seeking evidence by a survey of crystal structures.","author":"Henry Rzepa","date":"February 3, 2013","format":false,"excerpt":"The electronic interaction between a single bond and an adjacent double bond is often called \u03c3-\u03c0-conjugation (an older term for this is hyperconjugation), and the effect is often used to e.g. explain why more highly substituted carbocations are more stable than less substituted ones. This conjugation is more subtle in\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"C-H\/alkene interaction. 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