Immobilization of ruthenium benzylidene on thermoresponsive polymer: Methodology and application

• Synthesis of thermoresponsive ruthenium benzylidene compounds.
• Studies of Lower Critical Solution Temperature (LCST) of those compounds.
• Use as recoverable homogeneous metathesis catalyst in aqueous medium.

Attachment of metal complex on polymer has direct implication for the development of novel catalyst with recyclability, reusability and water solubility in the context environmental concern. In this paper, we illustrate a simple strategy to immobilize ruthenium benzylidene organometallic complex on thermoresponsive polymer. For this, pyridine-substituted poly (N-isopropylacrylamide) has been synthesized by atom transfer radical polymerization from a suitable initiator. Then, ruthenium benzylidene has been conjugated by binding with pyridine part of the polymer. Polymer conjugated ruthenium benzylidene is shown to have thermoresponsive characteristic in water (soluble below lower critical solution temperature (LCST) but precipitates out above LCST in water). Hence it can act as smart catalyst for metathesis reaction in water. For instance, it can be used as homogeneous metathesis catalyst for allyl alcohol in aqueous medium below lower critical solution temperature (LCST), that can be recovered as heterogeneous catalyst above LCST and recycled again as homogeneous catalyst. This is the first example of water-soluble recyclable metathesis catalyst. It is further demonstrated that steric crowding in the ligand play an important role in the superior performance of the catalyst.

Thermoresponsive ruthenium benzylidene compounds were prepared, which showed Lower Critical Solution Temperature (LCST) at 36–38 °C. It was used as homogeneous metathesis catalyst in aqueous medium below LCST, recovered as heterogeneous catalyst above LCST and further recycled as homogeneous catalyst.Figure optionsDownload as PowerPoint slide