Carbonyl olefination using readily prepared tungsten metallacycles

Area of Science:

• Organometallic Chemistry
• Catalysis
• Organic Synthesis

Background:

• Tungsten complexes are known catalysts for various organic transformations.
• Carbonyl olefination and ring-closing metathesis (CO/RCM) are important reactions for synthesizing cyclic compounds.
• Developing efficient catalysts for CO/RCM is an ongoing area of research.

Purpose of the Study:

• To synthesize and characterize a novel tungsten complex with a 6-membered metallacycle.
• To evaluate the catalytic activity of this complex and its derivatives in CO/RCM reactions.
• To explore the potential of cationic tungsten complexes for enhanced CO/RCM performance.

Main Methods:

• Synthesis of a tungsten-cyclooctyne complex, W(C8H12C8H12NAr)(NAr)Cl2 (1).
• Testing complex 1 and its derivatives (ethoxide, p-methoxyphenoxide, pentafluorophenoxide, chloride/triflate) for CO/RCM activity with a ketone and an ester substrate.
• Attempted synthesis of cationic tungsten complexes using Na[B(ArF)4] or AlCl3 for in situ testing.

Main Results:

• The synthesized dichloride complex (1) was found to be inactive for CO/RCM.
• Several neutral derivatives (2-5) were prepared and characterized, but their CO/RCM activity was not detailed.
• In situ generated cationic tungsten complexes exhibited very high activity for CO/RCM with the tested substrates.

Conclusions:

• The initial tungsten dichloride complex is not an effective CO/RCM catalyst.
• Cationic tungsten complexes, generated in situ, demonstrate significant potential as highly active catalysts for CO/RCM.
• Further investigation into the structure and catalytic mechanisms of these cationic species is warranted.