A Macrocyclic Ruthenium Carbene for Size-Selective Alkene Metathesis.

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Alkene metathesis is a powerful carbon-carbon bond-forming reaction.
• Developing selective catalysts for cross-metathesis remains a key challenge in organic synthesis.
• Macrocyclic ligands can influence catalyst reactivity and selectivity.

Purpose of the Study:

• To synthesize and characterize a novel macrocyclic ruthenium carbene catalyst.
• To investigate the catalyst's reactivity in homodimerization and cross-metathesis reactions.
• To demonstrate the catalyst's ability to achieve selective alkene differentiation based on steric factors.

Main Methods:

• Synthesis of a macrocyclic ruthenium carbene complex.
• Evaluation of catalyst performance in homodimerization of various type 1 alkenes.
• Testing the catalyst in competition cross-metathesis reactions involving different alkenes.
• Analysis of reaction outcomes to determine selectivity and substrate scope.

Main Results:

• The synthesized macrocyclic Ru catalyst exhibits distinct reactivity towards different type 1 alkenes in homodimerization.
• Reactivity in homodimerization correlates with the aggregate size of the allylic substituent.
• The catalyst demonstrates high selectivity in cross-metathesis reactions between sterically differentiated alkenes, such as tert-butyl acrylate.
• Two preparative examples showcase the catalyst's utility in selective cross-metathesis.

Conclusions:

• Macrocyclic design imparts unique reactivity and selectivity to Ru carbene catalysts for alkene metathesis.
• The catalyst's ability to differentiate alkenes by size is key to achieving selective cross-metathesis.
• This work provides a new tool for controlled synthesis via selective alkene metathesis.