Evidence for a Single Electron Shift in a Lewis Acid-Base Reaction

Area of Science:

• Organometallic Chemistry
• Main Group Chemistry
• Reaction Mechanisms

Background:

• Lewis acid-base reactions are fundamental in chemistry.
• Hafnocene-based compounds offer unique reactivity.
• Tris-pentafluorophenylborane is a strong Lewis acid.

Purpose of the Study:

• To investigate the reaction mechanism between a nucleophilic hafnocene-based germylene and tris-pentafluorophenylborane.
• To elucidate the role of radical intermediates in this Lewis acid-base reaction.
• To characterize the germanium radical cation and its electronic structure.

Main Methods:

• Single electron transfer studies
• Electron paramagnetic resonance (EPR) spectroscopy
• UV-vis spectroscopy
• X-ray diffraction (XRD) analysis
• Density Functional Theory (DFT) calculations

Main Results:

• The Lewis acid-base reaction proceeds via a single electron-transfer step, forming radical intermediates.
• A germanium radical cation was synthesized and characterized, revealing a hafnium(III)-centered radical.
• Redox-induced electron transfer (RIET) from the ligand to the hafnium atom causes valence isomerization, slowing product formation.

Conclusions:

• The reaction mechanism involves a surprising single electron transfer initiation.
• The formation of a hafnium(III) radical cation is a key intermediate step.
• This finding provides insights into radical pair formation in frustrated Lewis pairs.