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

A series of coinage metal complexes containing the redox-active metalloligands [RuCp<sup>X</sup>(κ<sup>3</sup><i>N</i>-Tpmd)] {κ<sup>3</sup><i>N</i>-Tpmd = κ<sup>3</sup><i>N</i>-[C­(pz)<sub>3</sub>] with pz = pyrazolyl; [RuCp­(Tpmd)] (<b>2a</b>) and [RuCp*­(Tpmd)] (<b>2b</b>)} are presented. <b>2a</b> and <b>2b</b> are isolable, relatively stable compounds, despite the fact that they feature a “naked” carbanion at the bridgehead position of the κ<sup>3</sup><i>N</i>-coordinated tris­(pyrazolyl)­methanide ligand scaffold. As expected, both complexes act as κ<sup>1</sup><i>C</i> ligands toward coinage metal fragments to yield dinuclear complexes of the general formula [RuCp<sup>X</sup>(μ-Tpmd)­{MX}] (μ-Tpmd = μ-κ<sup>1</sup><i>C</i>:κ<sup>3</sup><i>N</i>-[C­(pz)<sub>3</sub>]; M = Au, X = Cl, Cp<sup>X</sup> = C<sub>5</sub>H<sub>5</sub> (<b>3a</b>) or C<sub>5</sub>Me<sub>5</sub> (<b>3b</b>); M = Au, X = CN, Cp<sup>X</sup> = C<sub>5</sub>H<sub>5</sub> (<b>4a</b>) or C<sub>5</sub>Me<sub>5</sub> (<b>4b</b>); M = Cu, X = OC­(O)­Me, Cp<sup>X</sup> = C<sub>5</sub>H<sub>5</sub> (<b>5a</b>); M = Cu, X = Si­(SiMe<sub>3</sub>)<sub>3</sub>, Cp<sup>X</sup> = C<sub>5</sub>H<sub>5</sub> (<b>6a</b>) or C<sub>5</sub>Me<sub>5</sub> (<b>6b</b>); M = Ag, X = SC­(S)­NEt<sub>2</sub>, Cp<sup>X</sup> = C<sub>5</sub>H<sub>5</sub> (<b>7a</b>), M = Au, X = CC–Ar, Cp<sup>X</sup> = C<sub>5</sub>H<sub>5</sub> {Ar = C<sub>6</sub>H<sub>5</sub> (<b>8a</b>), 4-NH<sub>2</sub>-C<sub>6</sub>H<sub>4</sub> (<b>9a</b>), 3,5-(CF<sub>3</sub>)<sub>2</sub>-C<sub>6</sub>H<sub>3</sub> (<b>10a</b>)}). All complexes under study were fully characterized by common spectroscopic techniques; the structural parameters of <b>2a</b>, <b>3a</b>, <b>5a</b>, <b>6a</b>, <b>7a</b>, and <b>10a</b> were determined by X-ray diffraction. Coordination of the {MX} fragment leads to electronic effects on the metalloligand unit, as reflected by the corresponding <sup>1</sup>H and <sup>13</sup>C 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 <i>E</i><sup>0</sup><sub>1/2</sub>(Ru<sup>II</sup>/Ru<sup>III</sup>) value was detected with the aid of cyclic voltammetry measurements. A strong Lewis-acidic metal fragment such as GaCl<sub>3</sub> (<b>11a</b>) leads to an <i>E</i><sup>0</sup><sub>1/2</sub> value of 0.37 V, while electron-richer coinage metal fragments facilitate the oxidation of the ruthenium center significantly (<i>E</i><sup>0</sup><sub>1/2</sub> = 0.14–0.23 V). This dependence suggests an interaction between both metals due to their close spatial proximity.