Catalyst-Free Hydroboration of CO

Area of Science:

• Organometallic Chemistry
• Catalysis
• Green Chemistry

Background:

• Hydroboration reactions typically necessitate catalysts to facilitate hydride transfer.
• Developing catalytic or catalyst-free methods for CO2 functionalization is crucial for sustainable chemistry.

Purpose of the Study:

• To report the first instance of catalyst-free carbon dioxide (CO2) hydroboration using a neutral boron compound.
• To investigate subsequent hydroboration reactions and analyze reaction kinetics and influencing factors.

Main Methods:

• Utilized the nucleophilic diborane [HB(hpp)]2 (1) for CO2 hydroboration.
• Performed detailed kinetic measurements to study reaction rates.
• Analyzed the impact of solvent choice and Lewis base addition on reaction kinetics.

Main Results:

• Achieved catalyst-free hydroboration of CO2 with [HB(hpp)]2 (1).
• Demonstrated the possibility of further hydroboration to form bis(boryl)acetals.
• Observed solvent-dependent sequential hydroboration of two CO2 molecules in acetonitrile, but not in dichloromethane.
• Identified that acetone hydroboration, unlike CO2, requires a Lewis acid catalyst.

Conclusions:

• The neutral diborane [HB(hpp)]2 (1) is an effective reagent for catalyst-free CO2 hydroboration.
• Solvent and Lewis base interactions significantly influence the kinetics of CO2 hydroboration.
• This work provides a new pathway for CO2 utilization and highlights the unique reactivity of [HB(hpp)]2 (1) compared to less electrophilic substrates like acetone.