Canac, Y. et al. Isolation of a benzene valence isomer with one-electron phosphorus-phosphorus bonds. Science 279, 2080â2082 (1998).
Moret, M., Zhang, L. & Peters, J. C. A polar copperâboron one-electron Ï-bond. J. Am. Chem. Soc. 135, 3792â3795 (2013).
Hübner, A. et al. Confirmed by X-ray crystallography: the Bâ B one-electron Ï bond. Angew. Chem. Int. Ed. 53, 4832â4835 (2014).
Graziano, B. J. et al. One-electron bonds in copperâaluminum and copperâgallium complexes. Chem. Sci. 13, 6525â6531 (2022).
Ishigaki, Y., Shimajiri, T., Takeda, T., Katoono, R. & Suzuki, T. Longest CâC single bond among neutral hydrocarbons with a bond length beyond 1.8 Ã . Chem 4, 795â806 (2018).
Shimajiri, T. The Nature of Ultralong CâC Bonds (Springer Nature, 2023).
Pauling, L. The nature of the chemical bond. II. The one-electron bond and the three-electron bond. J. Am. Chem. Soc. 53, 3225â3237 (1931).
Lewis, G. N. The atom and the molecule. J. Am. Chem. Soc. 38, 762â785 (1916).
Langmuir, I. The arrangement of electrons in atoms and molecules. J. Franklin Inst. 187, 359â362 (1919).
Clark, T. Odd-electron .sigma. bonds. J. Am. Chem. Soc. 110, 1672â1678 (1988).
Ioffe, A. & Shaik, S. Ethane cation-radical isomers and their interconversion pathways. Electron shift isomerism in cation radicals. J. Chem. Soc., Perkin Trans. 2 3, 1461 (1993).
Zuilhof, H., Dinnocenzo, J. P., Reddy, C. & Shaik, S. Comparative study of ethane and propane cation radicals by B3LYP density functional and high-level ab initio methods. J. Phys. Chem. 100, 15774â15784 (1996).
de Sousa, D. W. O. & Nascimento, M. A. C. One-electron bonds are not âhalf-bondsâ. Phys. Chem. Chem. Phys. 21, 13319â13336 (2019).
Claxton, T. A., Overill, R. E. & Symons, M. C. R. Possible structures for C2H6+ and B2H6â E.S.R. evidence and UHF calculations. Mol. Phys. 27, 701â706 (1974).
DuPont, T. J. & Mills, J. L. Arylborane anions. Electrochemical study. J. Am. Chem. Soc. 97, 6375â6382 (1975).
Hudson, R. L. & Williams, F. Electron spin resonance spectrum of trimethyl borate ([(MeO)3B.cntdot.B(OMe)3]â). A novel .sigma. radical with a one-electron bond. J. Am. Chem. Soc. 99, 7714â7716 (1977).
Kasai, P. H. & McLeod, D. Electron spin resonance study of molecular anions generated in argon matrix at 4°K: ESR spectrum of B2H6â. J. Chem. Phys. 51, 1250â1251 (1969).
Iwasaki, M., Toriyama, K. & Nunome, K. Electron spin resonance study of electronic and geometrical structures of C2H6+ and other simple alkane cations at 4.2 K: possible evidence for JahnâTeller distortion. J. Am. Chem. Soc. 103, 3591â3592 (1981).
Wang, J. T. & Williams, F. E.S.R. spectra of the hexamethyldisilane and hexamethyldigermane radical cations. J. Chem. Soc. Chem. Commun. 1981, 666â668 (1981).
Shida, T., Kubodera, H. & Egawa, Y. Confirmation of the cation radicals of hexamethylethane and hexamethyldisilane by ESR and other spectroscopy. Chem. Phys. Lett. 79, 179â182 (1981).
Hoefelmeyer, J. D. & Gabbaï, F. P. An intramolecular boronâboron one-electron Ï-bond. J. Am. Chem. Soc. 122, 9054â9055 (2000).
Cataldo, L. et al. Formation of a phosphorusâphosphorus bond by successive one-electron reductions of a two-phosphinines-containing macrocycle: crystal structures, EPR, and DFT investigations. J. Am. Chem. Soc. 123, 6654â6661 (2001).
Rao, V. R. & Hixson, S. S. Arylcyclopropane photochemistry. Electron-transfer-mediated photochemical addition of methanol to arylcyclopropanes. J. Am. Chem. Soc. 101, 6458â6459 (1979).
Dinnocenzo, J. P., Todd, W. P., Simpson, T. R. & Gould, I. R. Nucleophilic cleavage of one-electron .sigma. bonds: stereochemistry and cleavage rates. J. Am. Chem. Soc. 112, 2462â2464 (1990).
Miyashi, T., Ikeda, H., Konno, A., Okitsu, O. & Takahashi, Y. Photoinduced electron-transfer reactions of the cope and related systems. Pure Appl. Chem. 62, 1531â1538 (1990).
Ikeda, H. et al. Photoinduced electron-transfer degenerate cope rearrangement of 2,5-diaryl-1,5-hexadienes: a cation-radical cyclizationâdiradical cleavage mechanism. J. Am. Chem. Soc. 120, 87â95 (1998).
Ikeda, H. et al. Photoinduced electron-transfer cope rearrangements of 3,6-diaryl-2,6-octadienes and 2,5-diaryl-3,4-dimethyl-1,5-hexadienes: stereospecificity and an unexpected formation of the bicyclo[2.2.0]hexane derivatives. J. Org. Chem. 64, 1640â1649 (1999).
Ikeda, H., Hoshi, Y. & Miyashi, T. 1,3-Bis(4-methoxyphenyl)cyclohexane-1,3-diyl cation radical: divergent reactivity depending upon electron-transfer conditions. Tetrahedron Lett. 42, 8485â8488 (2001).
Gomberg, M. Triphenylmethyl, ein Fall von dreiwerthigem Kohlenstoff. Ber. Dtsch. Chem. Ges. 33, 3150â3163 (1900).
Gomberg, M. An instance of trivalent carbon: triphenylmethyl. J. Am. Chem. Soc. 22, 757â771 (1900).
Kahr, B., Van Engen, D. & Mislow, K. Length of the ethane bond in hexaphenylethane and its derivatives. J. Am. Chem. Soc. 108, 8305â8307 (1986).
Takeda, T. et al. Hexaphenylethanes with an ultralong CâC bond: expandability of the CâC bond in highly strained tetraarylpyracenes. Chem. Lett. 42, 954â962 (2013).
Suzuki, T. et al. Expandability of ultralong CâC bonds: largely different C1âC2 bond lengths determined by low-temperature X-ray structural analyses on pseudopolymorphs of 1,1-bis(4-fluorophenyl)-2,2-bis(4-methoxyphenyl)pyracene. Chem. Lett. 43, 86â88 (2014).
Shimajiri, T., Suzuki, T. & Ishigaki, Y. Flexible CâC bonds: reversible expansion, contraction, formation, and scission of extremely elongated single bonds. Angew. Chem. Int. Ed. 59, 22252â22257 (2020).
Dyker, G., Hagel, M., Henkel, G. & Köckerling, M. Naphthyl-substituted carbocations: from peri interaction to cyclization. Eur. J. Org. Chem. 2008, 3095â3101 (2008).
Cordoneanu, A., Drewitt, M. J., Bavarian, N. & Baird, M. C. Synthesis and characterization of weakly coordinating anion salts of a new, stable carbocationic reagent, the dibenzosuberenyl (dibenzotropylium) ion. New J. Chem. 32, 1890 (2008).
Nishiuchi, T. et al. Anthraceneâattached persistent tricyclic aromatic hydrocarbon radicals. Chem. Asian J. 14, 1830â1836 (2019).
Sun, D., Rosokha, S. V. & Kochi, J. K. Donor-acceptor (electronic) coupling in the precursor complex to organic electron transfer: intermolecular and intramolecular self-exchange between phenothiazine redox centers. J. Am. Chem. Soc. 126, 1388â1401 (2004).
Small, D. et al. Intermolecular Ï-to-Ï bonding between stacked aromatic dyads. Experimental and theoretical binding energies and near-IR optical transitions for phenalenyl radical/radical versus radical/cation dimerizations. J. Am. Chem. Soc. 126, 13850â13858 (2004).
Nojo, W., Ishigaki, Y., Takeda, T., Akutagawa, T. & Suzuki, T. Selective formation of a mixed-valence state from linearly bridged oligo(aromatic diamines): drastic structural change into a folded columnar stack for half-filled polycations. Chem. Eur. J. 25, 7759â7765 (2019).
Casado, J. et al. Evidence for multicenter bonding in dianionic tetracyanoethylene dimers by Raman spectroscopy. Angew. Chem. Int. Ed. 52, 6421â6425 (2013).
Kubo, T. et al. Long carbon-carbon bonding beyond 2 Ã in Tris(9-fluorenylidene)methane. J. Am. Chem. Soc. 143, 14360â14366 (2021).
Dutan, C. et al. Electron transfer between two silyl-substituted phenylene rings: EPR/ENDOR spectra, DFT calculations, and crystal structure of the one-electron reduction compound of a Di(m-silylphenylenedisiloxane). J. Am. Chem. Soc. 125, 4487â4494 (2003).
Frisch, J. M. et al. Gaussian 16, Revision C.01 (Gaussian, Inc., 2019).
Lu, T. & Chen, F. Multiwfn: a multifunctional wavefunction analyzer. J. Comput. Chem. 33, 580â592 (2012).
Glendening, E. D., Reed, A. E., Carpenter, J. E. & Weinhold, F. NBO v.3.1 (Gaussian, Inc., 2001).
Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. OLEX2: a complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 42, 339â341 (2009).
Sheldrick, G. M. SHELXT â Integrated space-group and crystal-structure determination. Acta Crystallogr. A Found. Adv. 71, 3â8 (2015).
Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr. C Struct. Chem. 71, 3â8 (2015).
