Carbodiimide and Isocyanate Hydroboration by a Cyclic Carbodiphosphorane Catalyst

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Hydroboration reactions are crucial for synthesizing organoboron compounds.
• Carbodiimides and isocyanates are versatile synthetic intermediates.
• Developing efficient catalysts for hydroboration remains an active area of research.

Purpose of the Study:

• To investigate the catalytic activity of a cyclic carbodiphosphorane in hydroboration reactions.
• To explore the scope and selectivity of this catalytic system with carbodiimide and isocyanate substrates.
• To elucidate the mechanism of the hydroboration reaction.

Main Methods:

• Screening of Lewis basic carbon catalysts, including cyclic carbodiphosphoranes, phosphorus ylides, N-heterocyclic carbenes, and N-heterocyclic olefins.
• Hydroboration reactions of various carbodiimides and isocyanates using pinacolborane.
• Intermolecular competition experiments to assess substrate selectivity.
• Density Functional Theory (DFT) calculations to support mechanistic proposals.

Main Results:

• The cyclic carbodiphosphorane catalyst effectively catalyzed the hydroboration of seven carbodiimides and nine isocyanates at room temperature.
• The catalyst demonstrated superior performance compared to other tested Lewis basic carbon species.
• Selective hydroboration of alkyl isocyanates over carbodiimides and ketones was observed.
• DFT calculations supported a mechanism involving catalyst activation of pinacolborane and subsequent B-N bond formation.

Conclusions:

• Cyclic carbodiphosphoranes are highly effective catalysts for the hydroboration of carbodiimides and isocyanates.
• This methodology provides a facile route to N-boryl formamidines and N-boryl formamides.
• The catalyst exhibits excellent selectivity, offering a valuable tool for organic synthesis.