Redox‐Active Bisphosphines Based on a W(II)‐Propargyl Complex Backbone

Three bisphosphine ligands based on propargyl‐type alkyne complexes Tp*W (CO) (OR) η 2 ‐C 2 (CH 2 PPh 2) (PPh 2) Tp* = hydridotris (3, 4, 5‐trimethylpyrazolyl) borate with R = Me, Et, i Pr have been synthesized and characterized. The p K b values of the two phosphine groups were determined by conversion into the selenide derivative and determination of the 31 P/ 77 Se coupling constants. The methoxy‐substituted compound was utilized as a metalla‐ligand for preparation of a dinuclear bisphosphine κ 2 ‐PdCl 2 complex. The electrochemical properties were investigated using cyclic voltammetry (CV) and IR spectroelectrochemistry (IR‐SEC). The CV experiments of both the ligand and the Pd complex showed an electrochemically reversible W (II/III) redox couple, indicating that the W (III) species is stable on the voltammetry timescale. However, in both cases, IR‐SEC measurements disclosed a follow‐up process upon oxidation, showing that the W (III) compound undergoes a fast chemical transformation. Pure component decomposition of the IR‐SEC data was performed for kinetic analysis of the reaction profile. IR and mass spectrometric monitoring after stoichiometric oxidation as well as DFT calculations point to the formation of a W=O moiety by cleavage of the methoxy group leading to a subsequent disproportionation equilibrium.