R. Hoffmann and ;. M. Abe, J. Am. Chem. Soc, vol.90, p.7011, 1968.

, For a review on the quest for the observation and isolation of oxyallyl derivatives, see, Org. Chem. Front, vol.2, p.1536, 2015.

M. A. Thius, Eur. J. Org. Chem, vol.11, p.1, 1994.

F. G. Bordwell and J. G. Strong, Org. Biomol. Chem, vol.38, p.3109, 1973.

M. A. Harmata-;-m, P. M. Battiste, D. L. Pelphrey, . V. Wright-;-i, H. M. Hartung et al., Angew. Chem. Int. Ed, vol.12, p.6235, 1934.

M. G. Harmata-;-a, R. P. Lhose, and . Hsung, Chem. Commun, vol.46, p.3812, 2010.

E. J. Corey, S. P. Matsuda, R. Nagata, and M. B. Cleaver, Tetrahedron Lett, 1988.

O. Koljak, B. Boutaud, N. Shieh, A. R. Samel, . A. Brash-;-b et al., Org. Biomol. Chem, vol.277, p.2846, 1994.

T. Ichino, S. M. Villano, A. J. Gianola, D. J. Goebbert, L. Velarde et al., Angew. Chem. Int. Ed, vol.48, p.115, 1634.

G. Kuzmanich, F. Spänig, C. K. Tsai, J. M. Um, R. M. Hoekstra et al., J. Am. Chem. Soc, 2011.

T. Hirano, T. Kumagai, T. Miyashi, K. Akiyama, and Y. Ikegami, J. Am. Chem. Soc, vol.56, p.2804, 1907.

P. M. Matlin, D. Lahti, A. Appella, S. Straumanis, H. Lin et al., J. Am. Chem. Soc, p.2164, 1999.

T. Koide, K. Furukawa, H. Shinokubo, J. Shin, K. S. Kim et al., J. Am. Chem. Soc, vol.132, p.15533, 2010.

S. Sreejith, P. Carol, P. Chithra, A. Ajayaghosh-;-k.-ilina, W. M. Maccuaig et al., J. Mater. Chem, vol.18, p.194, 2008.

D. E. Lynch and D. G. Hamilton, Eur. J. Org. Chem, p.3897, 2017.

M. Tian, S. Tatsuura, M. Furuki, Y. Sato, I. Iwasa et al., For related dyes, in which the genuine oxyallyl nature is blurred by H-bonding, J. Am. Chem. Soc, vol.125, p.348, 2003.

D. Martin, C. E. Moore, A. L. Rheingold, and G. Bertrand, Angew. Chem. Int. Ed, vol.52, p.7014, 2013.

. Angew, . K. Chem-;-b)-j, D. Mahoney, F. Martin, C. Thomas et al., J. Am. Chem. Soc, vol.125, p.7519, 2013.

C. Farber, C. Bruhn, M. Leibold, D. Selent, W. Baumann et al., A related ferrocene-based derivative was isolated. However it is better described as a zwitterionic enol rather than an oxyallyl: U. Siemeling, p.697, 2010.

M. Devillard, V. Regnier, M. Tripathi, and D. Martin, J. Mol. Struct, p.3, 2018.

S. D. Ursula and U. Radius, Organometallics, vol.36, p.1398, 2017.

V. Regnier, F. Molton, C. Philouze, D. Martin, ;. Tripathi et al., Chem. Commun, vol.52, p.38346, 2016.

T. Schulz, C. Farber, M. Leibold, C. Bruhn, W. Baumann et al., For the isolation of a lithium complex, Chem. Commun, p.6834, 2013.

V. Regnier, Y. Planet, C. E. Moore, J. Pecaut, C. Philouze et al., Angew. Chem. Int, vol.56, p.1051, 1031.

M. Devillard, V. Regnier, J. Pecaut, and D. Martin, Org. Chem. Front, vol.6, pp.3184-3191, 2019.

T. Roth, V. Vasilenko, H. Wadepohl, D. S. Wright, and L. H. Gade, Inorg. Chem, vol.54, p.7636, 2015.

M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb et al., Calculations were performed with the Gaussian suite of programs: Gaussian09, Revision D.01, 2009.

J. Chai and M. Head-gordon, Phys. Chem. Chem. Phys, p.6615, 2008.

B. Gorodetsky, T. Ramnial, N. R. Branda, J. A. Clyburne, ;. Rottschäfer et al., Angew. Chem. Int Ed, vol.57, p.4855, 1972.

, Experimental values for isotropic hyperfine constants were extracted from EPR spectra by fitting with the EasySpin simulation package: S. Stoll, A. Schweiger, J. Magn. Reson, vol.178, p.42, 2006.

N. E. Hahn, M. C. Jahnke-;-c)-j, R. T. Lin, C. S. Huang, A. Lee et al., (i) N-Heterocyclic Carbenes: From Laboratory Curiosities to Efficient Synthetic Tools, Heterocyclic Carbenes-Effective Tools for Organometallic Synthesis, vol.47, p.485, 2007.

A. Fürstner, M. Alcarazo, H. Krause, C. W. Lehmann, J. Am et al., Angew. Chem. Int. Ed, vol.129, p.5271, 2007.

C. A. Tolman, Chem. Rev, vol.77, p.313, 1977.

D. G. Gusev and D. G. Gusev, Organometallics, vol.28, p.6458, 2009.

M. G. Hobbs, T. D. Forster, J. Borau-garcia, C. J. Knapp, H. M. Tuononen et al., Angew. Chem. Int. Ed, vol.34, p.6172, 2010.

A. Liske, K. Verlinden, H. Buhl, K. Schaper, C. ;. Ganter et al., Eur. J. Inorg. Chem, vol.32, p.6994, 2013.

O. Back, M. Henry-ellinger, C. D. Martin, D. Martin, and G. Bertrand, Angew. Chem. Int. Ed, vol.52, p.3011, 2013.

Y. G. Tretiakov, A. P. Shermolovich, P. P. Singh, H. W. Samuel, B. Roesky et al., It compares with cyclic (alkyl)amino)carbenes, see: M, p.12940, 2013.

C. M. Weinstein, G. P. Junor, D. R. Tolentino, R. Jazzar, M. Melaimi et al., Eur. J. Inorg. Chem, vol.140, p.3389, 2016.

, For a recent review on switchable and related "smart" NHC, see: E. Peris, Chem. Rev, vol.118, p.9988, 2018.

S. L. Balof, S. J. Pool, N. J. Berger, E. J. Valente, A. M. Shiller et al., For the use of proton-responsive NHC in catalysis, see : (a), vol.29, p.4339, 1786.

P. , V. R. Schleyer, C. Maerker, A. Dransfeld, H. Jiao et al., J. Am. Chem. Soc, vol.118, p.863, 1996.

C. P. Frizzo and M. A. Martins, Struct. Chem, p.375, 2012.

F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen et al., J. Chem. Soc. Perkin Trans. II, p.1, 1987.