Reducing and Reversing the Diphosphene-Diphosphinylidene Energy Separation

Area of Science:

• Computational Chemistry
• Inorganic Chemistry
• Quantum Chemistry

Background:

• Diphosphenes and diphosphinylidenes are phosphorus-containing compounds with unique bonding characteristics.
• Understanding the factors influencing their relative stability is crucial for predicting their reactivity and properties.

Purpose of the Study:

• To theoretically investigate the structural modifications and their impact on the relative energies of diphosphene and diphosphinylidene compounds.
• To determine the effect of various substituents on the parent PPH2 and HPPH molecules.

Main Methods:

• Theoretical calculations were employed to optimize geometries and determine relative energies.
• Isodesmic reaction energies were calculated for single and double substituent substitutions.
• Natural population analysis (NPA) and Natural Bond Orbital (NBO) analysis were used to explain bonding features.

Main Results:

• The diphosphinylidene structure was found to be more stable when both hydrogen atoms were substituted with lithoxy (OLi) or sodium oxy (ONa) groups.
• The lithoxy substitution resulted in an energy difference of 33 kcal/mol at the CCSD(T) cc-pVTZ level.
• A specific order of substituent effectiveness in lowering the diphosphinylidene structure's energy was established, with OLi being the most effective.

Conclusions:

• Lithoxy and sodium oxy substituents stabilize the diphosphinylidene structure over the diphosphene structure.
• Coulombic attraction plays a significant role in the stabilization provided by the lithoxy group.
• NBO analysis revealed significant phosphorus-phosphorus bond orders, indicating diverse bonding scenarios.