N‐Heterocyclic Carbene Analogues of Thiele and Chichibabin Hydrocarbons |
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| Authors: | Dennis Rottschäfer Nga Kim T. Ho Beate Neumann Dr. Hans‐Georg Stammler Dr. Maurice van Gastel Dr. Diego M. Andrada Priv.‐Doz.Dr. Rajendra S. Ghadwal |
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| Affiliation: | 1. http://www.ghadwalgroup.de;2. Anorganische Molekülchemie und Katalyse, Lehrstuhl für Anorganische Chemie und Strukturchemie, Centrum für Molekulare Materialien, Fakult?t für Chemie, Universit?t Bielefeld, Bielefeld, Germany;3. Max Planck Institut für Kohlenforschung, Mülheim an der Ruhr, Germany;4. Allgemeine und Anorganische Chemie, Universit?t des Saarlandes, Saarbrücken, Germany |
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| Abstract: | Stable N‐heterocyclic carbene analogues of Thiele and Chichibabin hydrocarbons, [(IPr)(C6H4)(IPr)] and [(IPr)(C6H4)2(IPr)] ( 4 and 5 , respectively; IPr=C{N(2,6‐iPr2C6H3)}2CHCH), are reported. In a nickel‐catalyzed double carbenylation of 1,4‐Br2C6H4 and 4,4′‐Br2(C6H4)2 with IPr ( 1 ), [(IPr)(C6H4)(IPr)](Br)2 ( 2 ) and [(IPr)(C6H4)2(IPr)](Br)2 ( 3 ) were generated, which respectively afforded 4 and 5 as crystalline solids upon reduction with KC8. Experimental and computational studies support the semiquinoidal nature of 5 with a small singlet?triplet energy gap ΔES?T of 10.7 kcal mol?1, whereas 4 features more quinoidal character with a rather large ΔES?T of 25.6 kcal mol?1. In view of the low ΔES?T, 4 and 5 may be described as biradicaloids. Moreover, 5 has considerable (41 %) diradical character. |
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| Keywords: | Chichibabin's hydrocarbons diradicaloids diradicals N-heterocyclic carbenes Thiele's hydrocarbons |
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