σ-Noninnocence: Masked Phenyl-Cation Transfer at Formal Ni^IV

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Reaction Mechanisms

Background:

• Reductive elimination is a key organometallic reaction involving a formal oxidation state change of -2 at a transition metal.
• Previous studies reported facile aryl-CF₃ bond formation via reductive elimination in high-valent Ni^IV complexes.

Purpose of the Study:

• To computationally analyze the mechanism of aryl-CF₃ bond formation in formal high-valent Ni^IV complexes.
• To investigate the role of σ-noninnocence in the observed reaction pathway.

Main Methods:

• Computational analysis of nickel complexes.
• Electron flow analysis to track charge transfer during the reaction.

Main Results:

• Formal Ni^IV centers are better described as Ni^II due to highly covalent metal-ligand bonds, a consequence of σ-noninnocence.
• The aryl-CF₃ bond formation occurs in an essentially redox-neutral manner, not a reductive elimination.
• Electron flow analysis indicates transfer of an anionic CF₃ group to an electrophilic aryl group.

Conclusions:

• σ-noninnocence significantly influences metal-ligand bonding and reaction pathways in these nickel complexes.
• The elimination process is essentially redox-neutral, challenging the conventional understanding of reductive elimination.
• These findings offer new concepts with broad relevance to elementary organometallic reaction steps.