Preparation and NMR Spectra of the (Trifluoromethyl)argentates(III) [Ag(CF3)nX4-n]-, with X = CN (n = 1-3), CH3, C≡CC6H11, Cl, Br (n = 2, 3), and I (n = 3), and of Related Silver(III) Compounds. Structures of [PPh4][trans-Ag(CF3)2(CN)2]

Article abstract of DOI:10.1021/ic9610445

Trifluoromethylation of [Ag(CN)₂]^- with (CF₃)₂Cd·diglyme yields [Ag(CF₃)(CN)]^-. The anion is readily oxidized by bromine to the argentates(III), [Ag(CF₃)_n(CN)_4-n]^-, n = 1-4. The stability of these species decreases with an increasing number of CN groups. Halogenation of these complexes with acetyl chloride or with bromine affords the moderately stable (n = 3) or unstable (n = 2) haloargentates of the type [Ag(CF₃)_nX_4-n]^-, X = Cl or Br. Their dehalogenation with AgNO₃ in a donor solvent D gives the adducts [Ag(CF₃)₃D] and [Ag(CF₃)₂D₂]⁺, respectively. Decomposition of most argentates(III) proceeds by reductive elimination of CF₃X (X = Cl, Br, or CN), but ligand exchange with participation of the CF₃ groups is also observed. The latter is used to prepare Ag(CF₃)₃ derivatives from the readily accessible [trans-Ag(CF₃)₂(CN)₂]^- anion. The syntheses of methyl-(trifluoromethyl)argentates(III) and of (cyclohexylethynyl)(trifluoromethyl)argentates(III) are accomplished by reaction of the cyanoargentates (n = 2, 3) with CH₃MgCl or LiC≡CC₆H₁₁, respectively. Often multinuclear (¹⁰⁹Ag, ¹⁹F, ¹³C, ¹H) NMR data of transient and stable Ag(III) species establish unambiguously not only their constitution but also the square-planar coordination of the metal. Couplings to the spin-1/2 silver nuclei are interpreted on the basis of 5s(Ag) orbital participation in competition with 4d orbital contributions to Ag-CF₃ bonding. Crystals of [PPh₄][Ag(CF₃)₂(CN)₂] belong to the monoclinic space group C2/c, with a = 18.174(2) A? b = 7.8881(8) A?, c = 18.881(2) A?, β = 93.036(8)°, and Z = 4, whereas [PPh₄][Ag(CF₃)₃(CH₃)] crystallizes in the orthorhombic space group Pca2₁, with a = 24.941(3) A?, b = 7.2629(6) A?, c = 14.9985(14) A?, and Z = 4. The coordination environments of these two argentates are approximately square planar. The Ag-CF₃ bonds in the dicyano complex (2.105(4) A?) are distinctly longer than the Ag-CN linkages (2.013(3) A?). In the [Ag(CF₃)₃(CH₃)]^- anion, the Ag-CH₃ distance (2.097(5) A?) is slightly shorter than the average Ag-CF₃ bond lengths (2.119(10) A?).