Tuning the potential of redox-active diphosphine ligands based on the alkyne complexes [TpW(CO)L{η-C(PPh)}]

Eleven complexes with the general formula [Tp*W(CO)L{η 2 -C 2 (PPh 2 ) 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 = CH 3 CN 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 31 P/ 77 Se coupling method of the corresponding diselenides. Selected examples of the dppa-complex ligands were converted into the corresponding κ 2 -PdCl 2 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 PdCl 2 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 PdCl 2 chelate complexes all determined by XRD shows the essential flexibility of the bend-back angles in the alkyne complex moiety. Variation of a single ligand in the W( ii ) alkyne complexes of bis(diphenylphosphino)acetylene leads to W( ii )/W( iii ) redox potentials spanning a window of 850 mV. The corresponding dinuclear complexes with PdCl 2 show differing catalytic activity.