Tris(pentafluoroethyl)difluorophosphorane for fluoride abstraction and ligand exchange reactions of N-heterocyclic carbene and cyclic alkyl(amino)carbene copper(i) fluorides

Abstract

The synthesis and structural characterization of a variety of N-heterocyclic carbene (NHC)- and cyclic (alkyl)(amino)carbene (cAAC)-ligated cationic copper(I) complexes, featuring the weakly coordinating tris(pentafluoroethyl)trifluorophosphate counteranion (FAP⁻ anion, [(C₂F₅)₃PF₃]⁻) are reported. Starting with the complex [(IDipp)Cu(C₆Me₆)]⁺FAP⁻ (IIa) reported previously, (S. A. Föhrenbacher, M. J. Krahfuss, L. Zapf, A. Friedrich, N. V. Ignat'ev, M. Finze and U. Radius, Chem. – Eur. J., 2021, 27, 3504-3516) a series of mononuclear complexes [(IDipp)Cu(LB)]⁺FAP⁻ (IDipp = 1,3-bis(2,6-di-iso-propylphenyl)-imidazolin-2-ylidene) were obtained via ligand exchange of C₆Me₆ with neutral two valence electron (2 VE) donor molecules (LB = NH₃, 1; C₆H₁₂N₂ = DABCO, 2; C₇H₁₀N₂ = DMAP, 3; C₄H₄N₂ = pyrazine, 4; C₁₃H₉N = acridine, 5; η¹-OC₁₃H₉N = acridone, 6; C₄H₁₀S = SEt₂, 7; C₄H₈S = THT, 8; PCy₃, 9), alongside the dinuclear species [{(IDipp)Cu}₂(C₂N₃H₃)₂]²⁺2FAP⁻ (10) with 1,2,4-triazole. In a parallel strategy, [(cAAC^Me)Cu(C₆Me₆)]⁺FAP⁻ (IIb) was employed as precursor for Cu(I) complex formation, leading to [(cAAC^Me)Cu(LB)]⁺FAP⁻ (LB = C₇H₁₀N₂, 13; C₄H₁₀S, 14) and the dinuclear complexes [{(cAAC^Me)Cu}₂(C₆H₁₂N₂)]²⁺2FAP⁻ (11) and [{(cAAC^Me)Cu}₂(C₄H₄N₂)]²⁺2FAP⁻ (12). Additionally, the reaction of [(carbene)CuF] with (C₂F₅)₃PF₂ in the presence of different 2 VE donor ligands induced fluoride replacement with a 2 VE donor ligand (LB). This strategy facilitated the isolation of a broad range of complexes of the type [(carbene)Cu(LB)]⁺FAP⁻, including [(IDipp)Cu(LB)]⁺FAP⁻ (LB = (NCMe)₂, 16; NCPh, 17; NH₂Ph, 18; NHPh₂, 21; NC₅H₅, 22; NC₅H₃F₂, 24; NC₅H₂F₃, 25; η¹-OCPh₂, 27), [(SIDipp)Cu(NH₂Ph)]⁺FAP⁻ (19) (SIDipp = 1,3-bis(2,6-di-iso-propylphenyl)-imidazolidin-2-ylidene) and [(cAAC^Me)Cu(LB)]⁺FAP⁻ (cAAC^Me = 1-(2,6-di-iso-propylphenyl)-3,3,5,5-tetramethyl-pyrrolidin-2-ylidene; LB = NCMe, 15; NH₂Ph, 20; NC₅H₅, 23; THF, 28). Additionally, the dinuclear complex [{(IDipp)Cu(μ-ONC₅H₅)}₂]²⁺2FAP⁻ (26) was obtained upon reaction with pyridine-N-oxide. In all cases the carbene ligand stayed intact and the formation of Lewis acid/base pairs of the 2 VE ligand and (C₂F₅)₃PF₂ was never observed. As a result, mixtures of [(carbene)CuF] and (C₂F₅)₃PF₂ may serve as synthons for [(carbene)Cu]⁺, as demonstrated in this work.