Proton-phosphorous connectivities revealed by high-resolution proton-detected solid-state NMR

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• Materials chemistry.
• Catalysis research.

Background:

• Proton-detected solid-state NMR offers atomic-level insights into solid-state reactions, crucial for understanding chemical mechanisms.
• Characterizing solid-state frustrated Lewis pairs (FLPs) is challenging but important due to their small molecule activation capabilities.
• Existing analytical methods for solid-state FLPs are limited, especially for detailed structural analysis.

Purpose of the Study:

• To introduce a novel phosphorus-31 radiofrequency channel for proton-detected solid-state NMR.
• To enhance the structural characterization of phosphane-borane frustrated Lewis pairs in the solid state.
• To demonstrate the utility of this method for analyzing complex solid-state reactions.

Main Methods:

• Implementation of a phosphorus-31 radiofrequency channel in proton-detected solid-state NMR.
• Utilizing fast magic-angle spinning (100 kHz) and high magnetic fields (850 and 1200 MHz).
• Performing solid-state 1H/31P and 1H/13C correlation experiments on PH-containing compounds.

Main Results:

• Successful characterization of four PH-containing phosphane-borane compounds.
• Revealed proton-phosphorus connectivities, indicating spatial proximity and chemical bonding.
• Identified unique proton chemical shifts attributed to intermolecular ring-current effects.
• Unambiguously distinguished three distinct phosphonium entities in a complex cyclotrimeric FLP associate.

Conclusions:

• The developed 31P spin-filtered proton-detected NMR approach provides valuable structural information for solid-state materials.
• This method significantly advances the analytical characterization of frustrated Lewis pairs and related compounds.
• The technique is broadly applicable to other material classes, including heterogeneous catalysts and general solid-state reactions.