A Co^II-Hydroxide Complex That Converts Directly to a Co^II-Acetamide during Catalytic Nitrile Hydration

Area of Science:

• Bioinorganic Chemistry
• Organometallic Chemistry

Background:

• Nitrile hydratases are crucial enzymes catalyzing nitrile hydration.
• Developing synthetic mimics of enzyme active sites aids in understanding biological mechanisms and designing new catalysts.
• Cobalt (Co) active sites in nitrile hydratases present unique structural and catalytic features.

Purpose of the Study:

• To synthesize and characterize novel pseudo-trigonal bipyramidal Co(II) complexes as structural and functional mimics of nitrile hydratases.
• To investigate the catalytic activity of these complexes in nitrile hydration reactions.

Main Methods:

• Synthesis of Co(II) complexes with a tetradentate tripodal ligand (LPh) and ancillary donors (DMF, acetate, hydroxide).
• Characterization using NMR, FT-IR, ESI-MS, electronic absorption spectroscopy, and X-ray crystallography.
• Catalytic studies involving acetonitrile hydration in the presence of hydroxide.

Main Results:

• Three pseudo-trigonal bipyramidal Co(II) complexes, 1(DMF), 1(OAc), and 1(OH), were successfully synthesized and characterized.
• Complex 1(OH) exhibits structural and functional resemblance to the Co active site of nitrile hydratases.
• 1(OH) reacted with acetonitrile to form a Co(II)-acetamide complex (2).
• 1(OH) catalyzed the quantitative conversion of hydroxide to acetamide with high selectivity and multiple turnovers, despite a different cobalt oxidation state compared to the enzyme.

Conclusions:

• The synthesized Co(II) complexes serve as valuable structural and functional models for nitrile hydratases.
• Complex 1(OH) demonstrates significant catalytic activity in nitrile hydration, mimicking the enzyme's function.
• This study highlights the potential of Co(II) complexes in developing efficient and selective nitrile hydration catalysts.