Easy Access to the Copper(III) Anion [Cu(CF₃)₄]⁻

Abstract

CuCl or pre‐generated CuCF3 reacts with CF3SiMe3/KF in DMF in air to give [Cu(CF3)4]− quantitatively. [PPN]+, [Me4N]+, [Bu4N]+, [PhCH2NEt3]+, and [Ph4P]+ salts of [Cu(CF3)4]− were prepared and isolated spectroscopically and analytically pure in 82–99 % yield. X‐ray structures of the [PPN]+, [Me4N]+, [Bu4N]+, and [Ph4P]+ salts were determined. A new synthetic strategy with [Cu(CF3)4]− was demonstrated, involving the removal of one CF3− from the Cu atom in the presence of an incoming ligand. A novel CuIII complex [(bpy)Cu(CF3)3] was thus prepared and fully characterized, including by single‐crystal X‐ray diffraction. The bpy complex is highly fluxional in solution, the barrier to degenerate isomerization being only 2.3 kcal mol−1. An NPA study reveals a huge difference in the charge on the Cu atom in [Cu(CR3)4]− for R=F (+0.19) and R=H (+0.46), suggesting a higher electron density on Cu in the fluorinated complex.

The Myth of d8 Copper(III)

“…Compounds 1−3 are covalency calibrants; 31−33 4−14 are crystallographically characterized, formally Cu II and Cu III species supported by C-, S-, N-, and/or O-donor ligands. 34,[36][37][38][39]59 Complexes 15−17 comprise a homologous redox series (Cu I /Cu II /Cu III ) recently reported by Betley and co-workers, 24 of which 17 represents the first definitive, terminal Cu nitrenoid species, relevant for under-standing Cu-catalyzed amination and aziridination reactions.…”

Csp3–Csp3 Bond-Forming Reductive Elimination from Well-Defined Copper(III) Complexes

“…[5][6][7][8][9][10][11][12] Therefore, significant amounts of work have been conducted to synthesize organocopper(III) complexes and understand their reactivity. [13][14][15][16][17][18][19][20][21] However, Cu III complexes with well-defined structures remain rather limited and most reported examples were stabilized by rigid macrocyclic chelating ligands or perfluorinated groups, 18,[22][23][24][25][26] few of which provide experimental evidence for reductive elimination of Cu III species to form C-C or C-heteroatom bonds. [27][28][29] Seminal work by Stahl and Ribas have shown that a series of Cu III -mono-aryl species stabilized by an electrondonating macrocyclic ligand can undergo C-heteroatom bondforming reductive elimination reactions.…”

“…22 Later, Cu III (CF 3 ) 4anion was first synthesized by Neumann 33 and, very recently, by Grushin using an optimized method. 18 Cu III -CF 3 complexes bearing nitrogen-containing ligands or a methyl group have recently been synthesized by Grushin 18 , Zhang [34][35][36] On the other hand, the unique properties of CF 3 groups in medicinal chemistry [38][39] have driven the development a large number of copper-promoted C-CF 3 bond-forming reactions. [40][41][42][43][44][45][46][47][48][49] In some of these reactions, C-CF 3 bond-forming reductive elimination from Cu III is indicated as the key step.…”

Copper-Catalyzed, Chloroamide-Directed Benzylic C–H Difluoromethylation

“…7 Recently, inspired by Li's groundbreaking work on the trifluoromethylation of alkyl radicals, 8 our group 9 and the Cook group 10 have independently reported the trifluoromethylation of benzylic C−H bonds using stoichiometric amounts of a Cu III −CF 3 reagent developed by Grushin. 11 A more recent milestone in the C(sp 3 )−H trifluoromethylation field was the discovery by the Li group that a combination of copper catalysts and Zn II −CF 3 reagents could enable catalytic trifluoromethylation of remote alkyl C−H bonds on N-fluoroamides 12 as well as unactivated benzylic C−H bonds. 13 On the other hand, analogous methods for C−H difluoromethylation have been lacking, in spite of the unique properties of a difluoromethyl group.…”