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Review
. 2019 Apr 8;10(18):4727-4741.
doi: 10.1039/c9sc01351b. eCollection 2019 May 14.

Stable cyclic (alkyl)(amino)carbene (cAAC) radicals with main group substituents

Subrata Kundu  1 , Soumen Sinhababu  1 , Vadapalli Chandrasekhar  1   2   3 , Herbert W Roesky  1
Affiliations
Review

Stable cyclic (alkyl)(amino)carbene (cAAC) radicals with main group substituents

Subrata Kundu et al. Chem Sci. .

Abstract

Isolation and characterization of stable radicals has been a long-pursued quest. While there has been some progress in this field particularly with respect to carbon, radicals involving heavier p-block elements are still considerably sparse. In this review we describe our recent successful efforts on the isolation of stable p-block element radicals particularly those involving aluminum, silicon, and phosphorus.

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Figures

Scheme 1
Scheme 1. Definition for disbiradicals and biradicals used in this article (reproduced from ref. 13a with permission from the Royal Society of Chemistry).
Fig. 1
Fig. 1. NHC ligated boryl monoradicals. The arrow indicates the donor–acceptor interaction.
Fig. 2
Fig. 2. cAAC ligated boryl mono- and biradicals.
Fig. 3
Fig. 3. cAAC-supported neutral aluminium monoradicals (20–22). As an example, a general synthesis and possible resonance structures of 20 are given.
Fig. 4
Fig. 4. Room-temperature (a) EPR spectrum of 20 simulation with (g = 2.0055), a(27Al) = 12.5 G; a(2 35,37Cl) = 1.9 G; a(2 14N) = 0.25 G; (b) EPR spectrum of compound 21 simulation with a(14N) = 4.3 G, a(27Al) = 8.3 G; (c) EPR spectrum of compound 22 at room temperature simulation with a(14N) = 4.95 G, a(27Al) = 5.2 G (Top: simulated spectrum and Bottom: experimental spectrum).
Fig. 5
Fig. 5. Oxidation of the thiazolylidene based enolate to a carbon-radical.
Fig. 6
Fig. 6. cAAC-derived carbon radicals.
Fig. 7
Fig. 7. Monoradical cations derived from cAACs.
Fig. 8
Fig. 8. Synthesis of di-cAAC stabilized C2˙+.
Fig. 9
Fig. 9. cAAC stabilized mono-, di- and biradicals over extended carbon systems.
Fig. 10
Fig. 10. NHC stabilized radicals over extended carbon systems.
Fig. 11
Fig. 11. cAAC coordinated SiR2 (R = Cl, Br, H, F) dis- and biradicals.
Fig. 12
Fig. 12. Synthesis of (cAAC˙)SiR3 (R = Cl, F or Ph).
Fig. 13
Fig. 13. cAAC-stabilized siladicarbene and in situ generation of (Me2cAAC)2Si˙–.
Fig. 14
Fig. 14. Silane-bridged dis- and biradicals.
Fig. 15
Fig. 15. cAAC-stabilized monoradical cation of Si(i).
Fig. 16
Fig. 16. cAAC stabilized group-15 radicals.
Fig. 17
Fig. 17. Radicals of silicon and phosphorus stabilized by cAAC.
Fig. 18
Fig. 18. Radical compounds of silicon and phosphorus stabilized by cAAC.
Fig. 19
Fig. 19. EPR spectrum of radical anion [(CycAAC)Si(P-Tip)]2˙– (64˙–) in toluene at 285 K.
Fig. 20
Fig. 20. Synthesis of oxyallyl radical cation 65˙+.
None
Subrata Kundu
None
Soumen Sinhababu
None
Vadapalli Chandrasekhar
None
Herbert W. Roesky
See this image and copyright information in PMC

References

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