M−C Bond Homolysis in Coinage‐Metal [M(CF₃)₄]⁻ Derivatives

Abstract

A comparative study of the homoleptic [M(CF3)4]− complexes of all three coinage metals (M=Cu, Ag, Au) reveals that homolytic M−C bond cleavage is favoured in every case upon excitation in the gas phase (CID‐MS2). Homolysis also occurs in solution by photochemical excitation. Transfer of the photogenerated CF3. radicals to both aryl and alkyl carbon atoms was also confirmed. The observed behaviour was rationalized by considering the electronic structure of the involved species, which all show ligand‐field inversion. Moreover, the homolytic pathway constitutes experimental evidence for the marked covalent character of the M−C bond. The relative stability of these M−C bonds was evaluated by energy‐resolved mass spectrometry (ERMS) and follows the order Cu<Ag≪Au. The qualitatively similar and rather uniform behaviour experimentally observed for all three coinage metals gives no ground to suggest variation in the metal oxidation state along the group.

σ‐Noninnocence: Masked Phenyl‐Cation Transfer at Formal NiIV

“…This leads to ligand oxidation and hence the presence of aformal and notably electrophilic "CF 3 + ", [5a] which originates from highly covalent metal-ligand s-bonds.Arecent study by Menjóna nd co-workers extended this interpretation of reduced oxidation states at the metal center to the [Ag-(CF 3 ) 4 ] À and [Au(CF 3 ) 4 ] À anions. [7] However, it should be noted that these earlier studies proposed the bonding model shown in Figure 1p rimarily via formal molecular-orbitaltheory considerations and generally identify the bonding and antibonding orbitals in Figure 1. We will argue below that this is often inappropriate in larger complexes or complexes of little symmetry,and that such considerations should be based on occupied and unoccupied localized valence molecular orbitals instead, rather than canonical molecular orbitals as presently done.…”

Unimolecular Reactivity of [Cu(R)(CF3)3]−Complexes (R=Organyl): Stepwise versus Concerted Mechanism in Copper‐Mediated Trifluoromethylation

“…Likewise, Baya et al. analyzed the gas‐phase fragmentation of [Cu(CF 3 ) 4 ] − and its heavier homologues [M(CF 3 ) 4 ] − (M=Ag and Au) [14] . Together, these studies demonstrated that the organocuprates can undergo concerted reductive eliminations and/or stepwise radical losses (Scheme 2, top).…”

“…Together, these studies demonstrated that the organocuprates can undergo concerted reductive eliminations and/or stepwise radical losses (Scheme 2, top). In particular, Baya et al [14] . showed that [Cu(CF 3 ) 3 ]⋅ − , the primary fragment ion of [Cu(CF 3 ) 4 ] − , readily released another CF 3 ⋅ radical.…”

“… Reported gas‐phase fragmentation of [Cu(CF 3 ) 4 ] − (top) [13b,14] and overview of the [Cu(R)(CF 3 ) 3 ] − complexes (C 3 H 5 =allyl) probed in this study (bottom).…”

[(MeCN)Ni(CF3)3]− and [Ni(CF3)4]2–: Foundations toward the Development of Trifluoromethylations at Unsupported Nickel

“…11 Menjon and coworkers showed that 1 can generate trifluoromethyl radicals under photolytic conditions, which could then be trapped by arenes and nitrones (Scheme 1b). 12 Importantly, the homoleptic tetra(trifluoromethyl)copper(III) functionality in 1 can also be rendered as heteroleptic derivatives (2) by the addition of nucleophiles to charge-neutral tris(trifluoromethyl) copper complexes (3, Scheme 1c). This derivatization is of high synthetic value because eliminations from 2 can render cross-coupled and trifluoromethylated organic products.…”