An actinide metallacyclopropene complex: synthesis, structure, reactivity, and computational studies

Area of Science:

• Organometallic Chemistry
• Actinide Chemistry
• Synthetic Inorganic Chemistry

Background:

• Actinide organometallic compounds are crucial for understanding fundamental chemical bonding and reactivity.
• Metallacyclopropenes are versatile intermediates in organic synthesis, but their actinide analogues are underexplored.
• Thorium complexes offer unique electronic properties due to the involvement of 5f orbitals.

Purpose of the Study:

• To synthesize and characterize the first stable actinide metallacyclopropene.
• To investigate the structural, electronic, and bonding properties of the synthesized complex.
• To explore the reactivity of the actinide metallacyclopropene with various unsaturated substrates and compare it with group 4 metals.

Main Methods:

• Synthesis via reduction of a thorium precursor with potassium graphite in the presence of diphenylacetylene.
• Structural characterization using magnetic susceptibility measurements.
• Computational analysis using density functional theory (DFT) to understand electronic structure and bonding.
• Reactivity studies with alkynes and heterounsaturated molecules.

Main Results:

• The first stable actinide metallacyclopropene, [η(5)-1,2,4-(Me3C)3C5H2]2Th(η(2)-C2Ph2), was successfully synthesized.
• Magnetic susceptibility confirmed the complex as a diamagnetic Th(IV) species.
• DFT calculations revealed significant contribution of Th 5f orbitals to the metallacyclopropene bonding.
• The complex showed no reactivity with alkynes but reacted with aldehydes, ketones, carbodiimides, nitriles, azides, and diazoalkanes.
• Thorium exhibited distinct reactivity patterns compared to group 4 metals.

Conclusions:

• The synthesis of a stable actinide metallacyclopropene opens new avenues in actinide organometallic chemistry.
• The electronic structure and bonding are influenced by the involvement of thorium's 5f orbitals.
• The unique reactivity profile of thorium metallacyclopropenes suggests potential applications in catalysis and synthesis.
• Thorium's distinct reactivity compared to group 4 metals highlights its unique position in the periodic table.