CO/CO and NO/NO coupling at a hidden frustrated Lewis pair template

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Boron compounds are versatile Lewis acids.
• Enamines are nucleophilic species capable of various reactions.
• The reactivity of enamines with Lewis acids and small molecules is an area of ongoing research.

Purpose of the Study:

• To investigate the reactivity of N-allyltetramethylpiperidine-derived enamine with boron Lewis acids.
• To explore the coupling reactions of the enamine/boron Lewis pair with carbon monoxide and nitric oxide.
• To synthesize and characterize novel heterocyclic compounds.

Main Methods:

• Isomerization of N-allyltetramethylpiperidine to its enamine using catalytic B(C6F5)3.
• Formation of a C/B Lewis adduct by the reaction of the enamine with HB(C6F5)2.
• Reaction of the Lewis adduct with carbon monoxide or nitric oxide.
• Characterization of products using X-ray diffraction.

Main Results:

• The enamine readily formed a C/B Lewis adduct with HB(C6F5)2.
• The enamine/HB(C6F5)2 Lewis pair reacted with two molar equivalents of carbon monoxide via head-to-tail coupling to yield a five-membered C2O2B heterocycle.
• In contrast, the reaction with two molar equivalents of nitric oxide proceeded via head-to-head coupling, likely through a vicinal N/B Lewis pair intermediate.

Conclusions:

• Catalytic B(C6F5)3 effectively isomerizes N-allyltetramethylpiperidine to the corresponding enamine.
• The enamine/HB(C6F5)2 Lewis pair exhibits distinct reactivity patterns with carbon monoxide and nitric oxide, leading to different heterocyclic products.
• The study demonstrates a novel synthetic route to C2O2B heterocycles and highlights the versatile reactivity of enamine/boron Lewis pairs.