Reversible intermolecular E-H oxidative addition to a geometrically deformed and structurally dynamic phosphorous...

Area of Science:

• Organophosphorus Chemistry
• Coordination Chemistry
• Inorganic Synthesis

Background:

• Tricoordinate phosphorus (σ(3)-P) compounds are fundamental in chemistry.
• Geometrical constraints can significantly influence phosphorus compound reactivity and properties.
• Tridentate triamide chelates offer unique steric and electronic environments for metal centers.

Purpose of the Study:

• To synthesize and characterize novel geometrically constrained tricoordinate phosphorus compounds.
• To investigate the inversion dynamics at the phosphorus center.
• To explore the reactivity of these compounds, particularly their oxidative addition capabilities.

Main Methods:

• Synthesis of tricoordinate phosphorus compounds supported by tridentate triamide chelates.
• Variable-temperature Nuclear Magnetic Resonance (NMR) spectroscopy to study phosphorus inversion.
• Density Functional Theory (DFT) calculations to elucidate inversion mechanisms.
• X-ray crystallography and multinuclear NMR spectroscopy for structural characterization of adducts.

Main Results:

• A Cs-symmetric tricoordinate phosphorus compound (2) was synthesized and structurally characterized.
• Low-energy phosphorus inversion (ΔG‡(exptl)(298) = 10.7(5) kcal/mol) was observed in solution.
• DFT calculations suggested an edge-inversion mechanism via a C2-symmetric intermediate.
• Compound 2 showed poor nucleophilicity but readily underwent oxidative addition with O-H and N-H compounds.
• Pentacoordinate adducts were formed, exhibiting structures spanning trigonal bipyramidal and square planar geometries.
• Oxidative addition was found to be reversible at elevated temperatures for volatile alcohols and amines.

Conclusions:

• Geometrically constrained tricoordinate phosphorus compounds can be synthesized with unique structural and dynamic properties.
• The observed low-energy inversion highlights the flexibility of the phosphorus center within the chelate.
• These compounds serve as versatile platforms for oxidative addition reactions, forming stable pentacoordinate adducts with potential applications in catalysis or materials science.