Understanding the Carbyne Formation from C₂H₂ Complexes

Area of Science:

• Organometallic Chemistry
• Bioinorganic Chemistry
• Catalysis

Background:

• Nature utilizes a high-valent tungsten center for acetylene hydration to acetaldehyde.
• Understanding tungsten-acetylene reactions is crucial for developing sustainable bioinspired catalysts.
• The precise mechanisms of tungsten-coordinated acetylene remain incompletely understood.

Purpose of the Study:

• To investigate the reactivity of two bioinspired tungsten complexes with acetylene.
• To elucidate the factors governing the distinct reaction pathways of tungsten-acetylene complexes.
• To gain insights into the enzyme acetylene hydratase's catalytic mechanism.

Main Methods:

• Synthesis and characterization of tungsten-acetylene complexes.
• Reaction studies with a phosphine nucleophile (PMe3).
• Spectroscopic and computational analyses to determine reaction mechanisms.

Main Results:

• A four-electron donor tungsten-acetylene complex formed a carbyne product via a 1,2-H shift.
• A two-electron donor tungsten-acetylene complex yielded a vinyl product, following typical alkyne complex reactivity.
• The PymS ligand was found to assist in the 1,2-H shift, and electron-poor, crowded tungsten centers favor nucleophilic attack.

Conclusions:

• Only four-electron donor acetylene complexes can form carbynes over vinyl intermediates.
• 1,2-H shifts in these systems can be facilitated by H-transfer reagents like the PymS ligand.
• The anionic PymS ligand's role highlights the potential involvement of amino acid residues in enzyme active sites.