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

A series of coinage metal complexes containing the redox-active metalloligands [RuCpX(κ3 N-Tpmd)] {κ3 N-Tpmd = κ3 N-[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 κ3 N-coordinated tris(pyrazolyl)methanide ligand scaffold. As expected, both complexes act as κ1 C ligands toward coinage metal fragments to yield dinuclear complexes of the general formula [RuCpX(μ-Tpmd){MX}] (μ-Tpmd = μ-κ1 C:κ3 N-[C(pz)3]; M = Au, X = Cl, CpX = C5H5 (3a) or C5Me5 (3b); M = Au, X = CN, CpX = C5H5 (4a) or C5Me5 (4b); M = Cu, X = OC(O)Me, CpX = C5H5 (5a); M = Cu, X = Si(SiMe3)3, CpX = C5H5 (6a) or C5Me5 (6b); M = Ag, X = SC(S)NEt2, CpX = C5H5 (7a), M = Au, X = CC–Ar, CpX = 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 E 0 1/2(RuII/RuIII) value was detected with the aid of cyclic voltammetry measurements. A strong Lewis-acidic metal fragment such as GaCl3 (11a) leads to an E 0 1/2 value of 0.37 V, while electron-richer coinage metal fragments facilitate the oxidation of the ruthenium center significantly (E 0 1/2 = 0.14–0.23 V). This dependence suggests an interaction between both metals due to their close spatial proximity.