Angewandte Chemie International Edition
10.1002/anie.201903496
COMMUNICATION
[
4]
Ligand-field inversion arises when the metal d orbitals are substantially
stabilized with respect to those contributed by the ligands and involves
inversion of the standard ligand-field splitting for any given geometry: R.
Hoffmann, S. Alvarez, C. Mealli, A. Falceto, T. J. Cahill, III, T. Zeng, G.
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•
The photogenerated CF
3
radicals can also be transferred to
simple organic molecules, showing therefore some potential
synthetic use. Thus, irradiation of 1a–1c in the presence of
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benzene as the most typical arene actually furnishes C
5) in modest yields (Scheme 2). If the mesitylene molecule is
used instead, trifluoromethylation is observed to take place not
6 5 3
H CF
(
2
3
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2
018, 24, 13098; b) W. Dukat, D. Naumann, Rev. Chim. Miner. 1986,
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3
2
molecules, we hope that this procedure can be further improved
and extended. It is worth noting that prolonged thermal
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treatment of 1b with C
6 6
H in the dark results in no detectable
CF transfer. The fact that chemical transformations induced by
3
photochemical activation are usually achieved under much
milder conditions than by thermal activation is a primary reason
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for the recent upsurge in the study of radical reactivity.
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In summary, the importance of radical reactivity in the
1
chemistry of the homoleptic trifluoromethyl complexes of
−
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trivalent coinage metals [M(CF
3
)
4
]
(1a–1c; M = Cu, Ag, Au) is
here demonstrated. All three compounds show rather
homogeneous behavior, with the observed differences being
more quantitative than qualitative in character. Thus, there is no
reason to set the copper compound 1a apart from its heavier-
metal homologues 1b and 1c. In fact, their electronic structures
all show ligand-field inversion as a distinctive feature (Figures 4
and S19). Perhaps the most important implication of this unusual
electronic arrangement is that the frontier orbitals, HOMO and
LUMO, are deeply involved in the M–C bond system. This is of
major chemical relevance. We demonstrate here that population
of the LUMO induced by thermal or photochemical activation
results in homolytic cleavage of the M–C bonds. Homolytic
splitting gives experimental proof of the marked covalent
character of the M–C bond in these high-valent compounds and
[
[
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denotes a breakdown of the ionic model (Scheme 1b).
[
[
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Acknowledgements
−
•
20] Complexes [CF
3 3 3
AuX ] (X = Cl, Br), were also found to undergo CF
−
dissociation in the gas phase giving rise to [AuX
3
] : M. Baya, A. Pérez-
This work was supported by the Spanish MICIU/FEDER (Project
PGC2018-094749-B-I00) and the Gobierno de Aragón (Groups
E14_R17 and E17_R17). We are indebted to ICMA researchers
Dr. Carlos Sánchez and Dr. Santiago Franco for the use of
valuable equipment. The Instituto de Biocomputación y Física de
Bitrián, S. Martínez-Salvador, A. Martín, J. M. Casas, B. Menjón, J.
Orduna, Chem. Eur. J. 2018, 24, 1514.
[
[
21] The ERMS technique enables to evaluate the strength of individual
bonds within chemical compounds of certain complexity: a) E. Altuntaș,
A. Winter, A. Baumgaertel, R. M. Paulus, C. Ulbricht, A. C. Crecelius, N.
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Sistemas
Complejos
(BIFI)
and
the
Centro
de
A. Winter, A. Crecelius, U. S. Schubert, Bruker App Note ET-34, 2012.
Supercomputación de Galicia (CESGA) are acknowledged for
allocation of computational resources. D. J.-S. also thanks the
Spanish MICIU for a grant (BES-2016-078732).
−
22] In an ion-trap mass spectrometer, the mass-selected [M(CF
3
)
4
]
anions
were subjected to CID conditions under variable collision energies,
which were gradually increased up to the point where the parent
complex was totally dissociated (see Experimental).
Keywords: coinage metals • homolysis • ligand-field inversion •
[23] The energy required to promote CF extrusion from the monovalent,
2
−
radicals • trifluoromethyl
linear [CF
3
MCF
3
]
complexes (3a–3c) was also evaluated (Figure S18).
I
I
I
In this case, the values obtained follow the order: Cu < Ag ~ Au.
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