Supramolecular-controlled regioselective photochemical [4 + 4] cycloaddition within Cp*Rh-based metallarectangles

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Organic Synthesis

Background:

• Photochemical reactions are crucial for synthesizing complex molecules, but controlling selectivity in anthracene derivatives remains challenging.
• Developing new methods for selective photoreactions is essential for advancing synthetic chemistry.

Purpose of the Study:

• To synthesize novel photoactive metallarectangles for controlled photochemical [4+4] cycloaddition of anthracene derivatives.
• To achieve high chemo- and regioselectivity in photoreactions using a rhodium template.
• To develop a reversible system for photodimer synthesis and dissociation.

Main Methods:

• Coordination-driven self-assembly of bifunctionalized anthracenes with a half-sandwich rhodium template.
• Photochemical irradiation at 365 nm to induce [4+4] cycloaddition.
• Photo- and thermal cleavage reactions to demonstrate reversibility.

Main Results:

• Synthesis of two photoactive metallarectangles (1a and 1b) via self-assembly.
• Exclusive photochemical [4+4] cycloaddition of preorganized anthracene units, yielding syn-photodimers in quantitative yields.
• Demonstration of reversible photocycloaddition and dissociation of photodimers from metalloassemblies up to three times.

Conclusions:

• Rhodium-templated metallarectangles effectively control the chemo- and regioselectivity of anthracene photoreactions.
• The developed system provides a highly efficient and reversible route for synthesizing anthracene photodimers.
• This approach facilitates the isolation of pure organic photodimers, overcoming limitations of conventional methods.