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

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journal contribution
posted on 30.11.2017, 21:45 by Kai Helmdach, Alexander Villinger, Wolfram W. Seidel
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 2O and 2S, the coordination behavior of these complex ligands differs substantially. XRD studies show that complex 2 and the sulfide 2S act 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 PdCl2 complex of the monoxide 2O is 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]2 with two equivalents of 2, which resulted in the iodide abstraction product [(2)­PdI2] (4).