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Issue 22, 2018
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Kekulé diradicaloids derived from a classical N-heterocyclic carbene

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Abstract

The direct double carbenylation of 1,4-diiodobenzene and 4,4′-dibromobiphenyl with a classical N-heterocyclic carbene, SIPr (1) (SIPr = :C{N(2,6-iPr2C6H3)}2CH2CH2), by means of nickel catalysis gives rise to 1,3-imidazolinium salts [(SIPr)(C6H4)(SIPr)](I)2 (2) and [(SIPr)(C6H4)2(SIPr)](Br)2 (3) as off-white solids. Two-electron reduction of 2 and 3 with KC8 cleanly yields Kekulé diradicaloid compounds [(SIPr)(C6H4)(SIPr)] (4) and [(SIPr)(C6H4)2(SIPr)] (5), respectively, as crystalline solids. Structural parameters and DFT as well as CASSCF calculations suggest the closed-shell singlet ground state for 4 and 5. Calculations reveal a very low singlet–triplet energy gap ΔES–T for 5 (10.7 kcal mol−1), while ΔES–T for 4 (29.1 kcal mol−1) is rather large.

Graphical abstract: Kekulé diradicaloids derived from a classical N-heterocyclic carbene

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Publication details

The article was received on 14 Mar 2018, accepted on 20 Apr 2018 and first published on 24 Apr 2018


Article type: Edge Article
DOI: 10.1039/C8SC01209A
Chem. Sci., 2018,9, 4970-4976
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    Kekulé diradicaloids derived from a classical N-heterocyclic carbene

    D. Rottschäfer, B. Neumann, H. Stammler, D. M. Andrada and R. S. Ghadwal, Chem. Sci., 2018, 9, 4970
    DOI: 10.1039/C8SC01209A

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