A Frustrated and Confused Lewis Pair.

Area of Science:

• Organometallic Chemistry
• Supramolecular Chemistry
• Catalysis

Background:

• Frustrated Lewis pairs (FLPs) are reactive species formed by the combination of sterically hindered Lewis acids and bases.
• FLPs have shown remarkable reactivity in small molecule activation and catalysis.
• The development of new FLP systems is crucial for expanding their synthetic utility.

Purpose of the Study:

• To report a new class of FLPs generated via hydroboration of bulky isocyanates.
• To investigate the structural and reactive properties of these novel FLP systems.
• To explore the potential for FLP behavior in systems lacking obvious Lewis acid-base frustration.

Main Methods:

• Hydroboration of bulky isocyanates (iPr2ArNCO and Ph2tBuArNCO) with Piers' borane (HB(C6F5)2).
• Isolation and characterization of isocyanate-N/B FLP adducts and substrate-free aminoboranes.
• High-level DFT studies and variable-temperature NMR spectroscopy to elucidate reaction pathways and intermediates.

Main Results:

• Hydroboration of iPr2ArNCO yielded isocyanate-N/B FLP adducts.
• Hydroboration of the bulkier Ph2tBuArNCO resulted in the isolation of a substrate-free aminoborane with a short N-B bond.
• This aminoborane, a 'confused' FLP, reversibly binds unsaturated substrates, indicating a transient 'normal' FLP intermediate.

Conclusions:

• A new class of FLPs has been synthesized through the hydroboration of sterically demanding isocyanates.
• The study demonstrates that FLP behavior can occur in systems not exhibiting typical Lewis acid-base pair frustration.
• These findings expand the scope of FLP chemistry and suggest novel avenues for catalyst design.