Issue 22, 2018

Kekulé diradicaloids derived from a classical N-heterocyclic carbene

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

Supplementary files

Article information

Article type
Edge Article
Submitted
14 Mar 2018
Accepted
20 Apr 2018
First published
24 Apr 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2018,9, 4970-4976

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

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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