A Comparative Theoretical Study of Water Reduction by B/P-Based Frustrated Lewis Pairs

Area of Science:

• Computational Chemistry
• Materials Science
• Green Chemistry

Background:

• Traditional water splitting methods often rely on transition-metal complexes.
• P-block compounds, particularly boron-phosphorus-based frustrated Lewis pairs (FLPs), are emerging as alternatives for water reduction.
• Prior research established bisborylphosphine (BPB) and borylphosphine (BP) systems within FLP chemistry.

Purpose of the Study:

• To computationally model the nucleophilic substitution step in water splitting using DFT.
• To elucidate mechanistic details and substituent effects on reaction energy barriers for BPB and BP systems.
• To derive design principles for efficient water splitting catalysts.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to model water splitting reactions.
• Reaction profiles were computed for BPB and BP systems.
• Systematic variation of substituents on borane (R1) and phosphorus (R2) was performed to analyze steric and electronic effects.

Main Results:

• The BPB systems consistently exhibited lower energy barriers for nucleophilic substitution compared to BP systems.
• Distortion-Interaction analysis revealed greater geometric distortion in intermolecular borane receptors (BP) versus intramolecular ones (BPB).
• Electron-donating substituents on the phosphorus atom (R2) significantly reduced the energy barriers for BP systems, making them competitive with BPB.

Conclusions:

• The intramolecular nature of the borane receptor in BPB contributes to its lower activation energy for water splitting.
• Substituent effects play a critical role in tuning the reactivity of BP systems.
• Tailoring phosphorus substituents offers a viable strategy to enhance the catalytic efficiency of BP systems for water splitting.