Heterobimetallic cuprates consisting of a redox-switchable, silicon-based metalloligand: synthesis, structures, and electronic properties

A series of bimetallic silyl halido cuprates consisting of the new tripodal silicon-based metalloligand [κ(3)N-Si(3,5-Me2pz)3Mo(CO)3](-) is presented (pz = pyrazolyl). This metalloligand is straightforwardly accessible by reacting the ambidentate ligand tris(3,5-dimethylpyrazolyl)silanide ({Si(3,5-Me2pz)3}(-)) with [Mo(CO)3(η(6)-toluene)]. The compound features a fac-coordinated tripodal chelating ligand and an outward pointing, "free" pyramidal silyl donor, which is easily accessible for a secondary coordination to other metal centers. Several bimetallic silyl halido cuprates of the general formula [CuX{μ-κ(1)Si:κ(3)N-Si(3,5-Me2pz)3Mo(CO)3}](-) (X = Cl, Br, I) have been synthesized. The electronic and structural properties of these complexes were probed in detail by X-ray diffraction analysis, electrospray mass spectrometry, infrared-induced multiphoton dissociation studies, cyclic voltammetry, spectroelectrochemistry, gas-phase photoelectron spectroscopy, as well as UV/Vis and fluorescence spectroscopy. The heterobimetallic complexes contain linear two-coordinate copper(I) entities with the shortest silicon-copper distances reported so far. Oxidation of the anionic complexes in methylene chloride and acetonitrile solutions at E(1/2)(0( = -0.60 and -0.44 V (vs. ferrocene/ferrocenium (Fc/Fc(+))), respectively, shows substantial reversibility. Based on various results obtained from different characterization methods, as well as density functional theory calculations, these oxidation events were attributed to the Mo(0)/Mo(I) redox couple.