Related Experiment Videos
Diradical Character Enhancement by Spacing: N-Heterocyclic Carbene Analogues of Müller's Hydrocarbon
Dennis Rottschäfer1, Jasmin Busch1, Beate Neumann1
1Anorganische Molekülchemie und Katalyse, Lehrstuhl für Anorganische Chemie und Strukturchemie, Centrum für Molekulare Materialien, Fakultät für Chemie, Universität Bielefeld, Universitätsstrasse 25, 33615, Bielefeld, Germany.
Abstract:
Two-fold C-C cross-coupling of N-heterocyclic carbenes [NHCs; SIPr=C(NArCH2 )2 , 1; IPr=C(NArCH)2 , 2; Me-IPr=C(NArCMe)2 , 3; Ar=2,6-iPr2 C6 H3 ] with 4,4''-diiodo-p-terphenyl under Ni catalysis furnished [(SIPr)(C6 H4 )3 (SIPr)](I)2 (4), [(IPr)(C6 H4 )3 (IPr)](I)2 (5), and [(Me-IPr)(C6 H4 )3 (Me-IPr)](I)2 (6). Two-electron reduction of 4-6 with KC8 readily afforded NHC analogues of Müller's hydrocarbon (MH), [(SIPr)(C6 H4 )3 (SIPr)] (7), [(IPr)(C6 H4 )3 (IPr)] (8), and [(Me-IPr)(C6 H4 )3 (Me-IPr)] (9), respectively, as highly colored crystalline solids. Quantum chemical calculations suggested that the singlet ground state for 7-9 possesses a vertical singlet-triplet energy gap ΔES-T of -7.24 to -7.60 kcal mol-1 , which is significantly lower compared to that of the NHC analogues of Thiele's (TH) and Chichibabin's (CH) (18-38 kcal mol-1 ) hydrocarbons. Importantly, the calculated diradical character (y) of 7-9 (y≈0.6) is considerably higher compared to that of the related TH and CH (y=0.1-0.4), suggesting the open-shell singlet character of 7-9.