Coinage Metal Complexes of Tris(pyrazolyl)methanide-Based Redox-Active Metalloligands

A series of coinage metal complexes containing the redox-active metalloligands [RuCp^X(κ³N-Tpmd)] {κ³N-Tpmd = κ³N-[C­(pz)₃] with pz = pyrazolyl; [RuCp­(Tpmd)] (2a) and [RuCp*­(Tpmd)] (2b)} are presented. 2a and 2b are isolable, relatively stable compounds, despite the fact that they feature a “naked” carbanion at the bridgehead position of the κ³N-coordinated tris­(pyrazolyl)­methanide ligand scaffold. As expected, both complexes act as κ¹C ligands toward coinage metal fragments to yield dinuclear complexes of the general formula [RuCp^X(μ-Tpmd)­{MX}] (μ-Tpmd = μ-κ¹C:κ³N-[C­(pz)₃]; M = Au, X = Cl, Cp^X = C₅H₅ (3a) or C₅Me₅ (3b); M = Au, X = CN, Cp^X = C₅H₅ (4a) or C₅Me₅ (4b); M = Cu, X = OC­(O)­Me, Cp^X = C₅H₅ (5a); M = Cu, X = Si­(SiMe₃)₃, Cp^X = C₅H₅ (6a) or C₅Me₅ (6b); M = Ag, X = SC­(S)­NEt₂, Cp^X = C₅H₅ (7a), M = Au, X = CC–Ar, Cp^X = C₅H₅ {Ar = C₆H₅ (8a), 4-NH₂-C₆H₄ (9a), 3,5-(CF₃)₂-C₆H₃ (10a)}). All complexes under study were fully characterized by common spectroscopic techniques; the structural parameters of 2a, 3a, 5a, 6a, 7a, and 10a were determined by X-ray diffraction. Coordination of the {MX} fragment leads to electronic effects on the metalloligand unit, as reflected by the corresponding ¹H and ¹³C NMR spectra. Density functional theory calculations were performed in order to elucidate a conceivable interplay between the metal atoms. The bonding characteristics within the {MX} fragment are only marginally affected upon electronic excitation of the ruthenium-based metalloligand. However, some effect of the influence of {MX} on the E⁰_1/2(Ru^II/Ru^III) value was detected with the aid of cyclic voltammetry measurements. A strong Lewis-acidic metal fragment such as GaCl₃ (11a) leads to an E⁰_1/2 value of 0.37 V, while electron-richer coinage metal fragments facilitate the oxidation of the ruthenium center significantly (E⁰_1/2 = 0.14–0.23 V). This dependence suggests an interaction between both metals due to their close spatial proximity.