Enhancing Diradical Character of Chichibabin's Hydrocarbon through Fluoride Substitution

Abstract In this work, 5‐SIDipp [SIDipp=1,3‐bis(2,6‐diisopropylphenyl)‐imidazolin‐2‐ylidene] ( 1 ) derived Chichibabin's hydrocarbon with an octafluorobiphenylene spacer ( 3 ) has been reported. The addition of two equivalents of 5‐SIDipp with decafluorobiphenyl in presence of BF 3 gives the double C−F bond activated imidazolium salt with two tetrafluoroborate anions, 2 . Further reduction of 2 gives the fluorine substituted 5‐SIDipp based Chichibabin's hydrocarbon, 3 . Quantum chemical calculations suggested a singlet state of 3 with a singlet–triplet energy gap (Δ E S‐T ) of 3.7 kcal mol −1 , which is substantially lower with respect to the hydrogen substituted NHC‐based Chichibabin's hydrocarbons (10.7 kcal mol −1 , B3LYP). As a result, the diradical character (y) of 3 (y=0.62) is also noticeably higher than the hydrogen substituted CHs (y=0.41–0.43). The ▵E S‐T was found to be higher in CASSCF (22.24 kcal mol −1 ) and CASPT2 (11.17 kcal mol −1 ) for 3 and the diradical character (d) is 44.6 %.