Exploring Regioselective Bond Cleavage and Cross-Coupling Reactions using a Low-Valent Nickel Complex

Area of Science:

• Organometallic Chemistry
• Catalysis
• Synthetic Organic Chemistry

Background:

• Esters are increasingly utilized as transmetalation agents in cross-coupling reactions.
• Nickel(0) complexes offer versatile reactivity for organic transformations.

Purpose of the Study:

• To systematically investigate the reactivity of diverse esters and thioesters with a nickel(0) source.
• To explore the potential of these reactions in catalytic cross-coupling.

Main Methods:

• Reaction of various esters and thioesters with [{(dtbpe)Ni}2(μ-η(2):η(2)-C6H6)] (a source of (dtbpe)nickel(0)).
• Characterization of intermediate nickel complexes.
• Stoichiometric cross-coupling reactions with phenylboronic acid.
• Investigation of factors hindering catalytic turnover.

Main Results:

• Trifluoromethylthioesters formed η(2)-carbonyl complexes.
• Acetylthioesters underwent C-S bond cleavage and decarbonylation, forming methylnickel species, reversible with CO.
• Thioester complexes yielded sulfides via cross-coupling with phenylboronic acid.
• Phenyl esters underwent C-O bond cleavage yielding arylnickel complexes, which coupled to form biaryls.
• Catalytic attempts were impeded by ligand scrambling, forming nickel bis(acetate) complexes.

Conclusions:

• Esters and thioesters exhibit distinct reactivity patterns with nickel(0) complexes.
• Stoichiometric cross-coupling is feasible, but catalytic applications face challenges like ligand scrambling.
• Further development is needed to achieve efficient catalytic cross-coupling using these substrates.