The Influence of Stepwise P-Oxidation on the Coordination and Redox Behavior of W–Bisphosalkyne Complex Ligands

The terminal phosphine groups at the tungsten bisphosphine alkyne complex [Tp*W(CO)(I)(η2-C,C′-Ph2PC2PPh2)] (2) {Tp* = hydridotris(3,4,5-trimethylpyrazolyl)borate} were selectively oxidized by common methods to form the alkyne complexes 2EE(E = O, S) with either two phosphine oxide or two phosphine sulfide substituents. The respective mono-oxidized analogues 2E(E = O, S) were obtained by subjecting the already oxidized intermediates [Tp*W(CO)(I)(η2-C,C′-Ph2P(E)C2H)] 1E(E = O, S) to a late-stage phosphine introduction at the complex template. These modulations of the peripheral alkyne moiety have a clear impact on the redox potential of the metal-based oxidation altering the W(II/III) potential by +0.1 V on average per oxidized phosphine. In contrast to the comparable redox behavior of 2Oand 2S, the coordination behavior of these complex ligands differs substantially. XRD studies show that complex 2and the sulfide 2Sact either as a P,P’- or P,S-chelate ligand leading to the dinuclear complexes [(2)PdCl2], 3, and [(2S)PdCl2], 3S. In contrast, the corresponding PdCl2complex of the monoxide 2Ois connected by the free phosphine group and the W-bonded iodide as a μ2-bridging ligand leaving the phosphine oxide pending. A similar binding mode was found for the trinuclear gold complex [(2)2Au][PF6] (5-PF6). Furthermore, these findings explain the undesired outcome in the reaction of [Pd(NCMe)4][BF4]2with two equivalents of 2, which resulted in the iodide abstraction product [(2)PdI2] (4).