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Journal Article

Stabilizing P≡P: P22–, P2⋅–, and P20 as bridging ligands


Tkach,  I.
Research Group of Electron Paramagnetic Resonance, MPI for biophysical chemistry, Max Planck Society;

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Sun, J., Verplancke, H., Schweizer, J. I., Diefenbach, M., Würtele, C., Otte, M., et al. (2021). Stabilizing P≡P: P22–, P2⋅–, and P20 as bridging ligands. Chem, 7(7), 1952-1962. doi:10.1016/j.chempr.2021.06.006.

Cite as: https://hdl.handle.net/21.11116/0000-0009-AC59-2
The bigger picture: Chemical synthesis relies on strategies to stabilize well-defined molecular building blocks while also retaining their fundamental reactivity. This is illustrated by the classic pnictogen dichotomy. In contrast to highly stable N2, the higher homologs Pn2 evade isolation—and thus synthetic use—as a result of the preference of heavier p-block elements for σ-bonding. Previous strategies to stabilize π-bonded compounds such as P2 by coordination to electron donors have significantly altered their bonding and reactivity. Here, we demonstrate the coordination of redox-inactive transition-metal fragments as a strategy to stabilize P2 under ambient conditions with retention of the P≡P triple bond character, as in the case of free P2. The release of the Lewis-acidic capping agents offers P2 transfer reactivity to molecular products. This work provides a new strategy for the stabilization of highly reactive species with multiply bonded heavy p-block elements and their use as reagents in chemical synthesis.

Summary: In contrast to its lighter congener N2, neutral diphosphorus with a P≡P triple bond is a highly reactive species observable only in the gas phase and by matrix isolation. Previous stabilization efforts with Lewis bases (e.g., carbenes) or by transition-metal coordination led to charge transfer to highly electrophilic P2 and thus to significant reduction of the bond order. Here, we report the crystallographic, spectroscopic, and quantum chemical characterization of the redox series [(μ2,η1:η1-P2){Pt(PNP)}2] (PNP = N(CHCHPtBu2)2), which features (P2)2–, (P2)⋅–, and (P2)0 as bridging ligands. Although common for N2, the stabilization as a neutral, triply bonded P≡P ligand is unprecedented for the heavier homolog. It was enabled by coordination of the dipnictogen to redox-inactive Lewis-acidic metal fragments and gave rise to the controlled release of P2 in the condensed phase.