Mechanism Analysis: Oxidative Addition and Reductive Elimination

The question asks to identify a reaction proceeding via oxidative addition followed by reductive elimination. These are key steps in many organometallic catalytic cycles.

• Oxidative Addition involves an increase in the metal's oxidation state (usually by two) and coordination number.
• Reductive Elimination involves a decrease in the metal's oxidation state (usually by two) and coordination number, forming a new bond between ligands.

Evaluating Reaction Schemes

Let's analyze the provided reaction images:

• Option 1 (Ni): Shows a nickel-catalyzed reaction, likely coupling.
• Option 2 (Ta): Shows a tantalum-mediated reaction.
• Option 3 (Zr): Shows a zirconium-catalyzed reaction.
• Option 4 (Pt): This scheme depicts a catalytic cycle starting with a Platinum (Pt) complex, presumably in a low oxidation state (e.g., Pt(0)). The reaction involves:
  1. The addition of an R-X species across the metal center, leading to an increase in the metal's oxidation state (e.g., to Pt(II)) - this is oxidative addition.
  2. Subsequent steps lead to the formation of an R-R bond, accompanied by a decrease in the metal's oxidation state back to the initial state (e.g., Pt(0)) - this is reductive elimination.
  This sequence explicitly demonstrates both oxidative addition and reductive elimination as core steps.

Conclusion

The reaction scheme presented in Option 4 clearly illustrates a catalytic cycle driven by the fundamental steps of oxidative addition followed by reductive elimination, commonly observed in cross-coupling reactions catalyzed by metals like platinum.