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N‐Heterocyclic Carbene Analogues of Thiele and Chichibabin Hydrocarbons
Author(s) -
Rottschäfer Dennis,
Ho Nga Kim T.,
Neumann Beate,
Stammler HansGeorg,
van Gastel Maurice,
Andrada Diego M.,
Ghadwal Rajendra S.
Publication year - 2018
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201713346
Subject(s) - carbene , diradical , chemistry , singlet state , medicinal chemistry , catalysis , photochemistry , organic chemistry , physics , excited state , nuclear physics
Stable N‐heterocyclic carbene analogues of Thiele and Chichibabin hydrocarbons, [(IPr)(C 6 H 4 )(IPr)] and [(IPr)(C 6 H 4 ) 2 (IPr)] ( 4 and 5 , respectively; IPr=C{N(2,6‐ i Pr 2 C 6 H 3 )} 2 CHCH), are reported. In a nickel‐catalyzed double carbenylation of 1,4‐Br 2 C 6 H 4 and 4,4′‐Br 2 (C 6 H 4 ) 2 with IPr ( 1 ), [(IPr)(C 6 H 4 )(IPr)](Br) 2 ( 2 ) and [(IPr)(C 6 H 4 ) 2 (IPr)](Br) 2 ( 3 ) were generated, which respectively afforded 4 and 5 as crystalline solids upon reduction with KC 8 . Experimental and computational studies support the semiquinoidal nature of 5 with a small singlet−triplet energy gap Δ E S−T of 10.7 kcal mol −1 , whereas 4 features more quinoidal character with a rather large Δ E S−T of 25.6 kcal mol −1 . In view of the low Δ E S−T , 4 and 5 may be described as biradicaloids. Moreover, 5 has considerable (41 %) diradical character.