Tuning the potential of redox-active diphosphine ligands based on the alkyne complexes [Tp*W(CO)L{η2-C2(PPh2)2}]

Eleven complexes with the general formula [Tp*W(CO)L{eta(2)-C-2(PPh2)(2)}](n+) {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)-borate, L = F-, Cl-, Br-, I-, MeS-, PhS-, pyCH(2)S(-), CN- and TfO-; n = 0 and L = CH3CN and pyridine; n = 1} have been synthesized and fully characterized. Depending on L, the oxidation process from W(ii) to W(iii) is detected between -0.28 and +0.55 V vs. Fc/Fc(+) and the spectroscopic properties (X-ray, IR, and NMR) are influenced according to the electron-rich or electron-poor character of the central metal. The basicity of the alkyne complex-based phosphine groups was estimated by the P-31/Se-77 coupling method of the corresponding diselenides. Selected examples of the dppa-complex ligands were converted into the corresponding kappa(2)-PdCl2 chelate complexes and employed in a Sonogashira reaction in order to estimate the effect of L on the catalytic behaviour of the dinuclear complexes. While the spectroscopic properties show a good correlation with the redox potential in a mostly linear fashion, catalytic activity is influenced only slightly. The effect of PdCl2 coordination on the alkyne complex is evident from the W(ii)/W(iii) redox potentials measured by cyclic voltammetry supported by a change of the CO stretching frequency in IR. A comparison of the molecular structures of the alkyne complexes with terminal phosphine groups and the PdCl2 chelate complexes all determined by XRD shows the essential flexibility of the bend-back angles in the alkyne complex moiety.

Automated summary

Eleven complexes bearing the general formula [Tp*W(CO)L{η(2)-C-2(PPh2)(2)}](n+) have been synthesized and fully characterized. The oxidation process and spectroscopic properties of the complexes are influenced by the electron character of the central metal. The basicity of the phosphine groups in the alkyne complexes is estimated. The coordination of PdCl2 affects the redox potentials and catalytic activity. X-ray diffraction analysis shows the flexibility of the alkyne complex moiety.