Phenylalanine (1), which could be potentially obtained from biofuel waste streams, is a precursor of cinnamic acid (2) that can be converted into two bulk chemicals, styrene (3) and acrylic acid (4), via an atom efficient pathway. With 5 mol% of Hoveyda-Grubbs 2nd generation catalyst, 1 bar of ethylene, and using dichloromethane as solvent, cinnamic acid (2) can be converted to acrylic acid and styrene at 40°C in 24 h with 13% conversion and 100% selectivity. Similar results are obtained using cinnamic acid esters (methyl, ethyl and n-butyl) as substrates and optimisation leads to higher conversions (up to 38%). For the first time, cross-metathesis of these types of electron deficient substrates was achieved.
The desire to utilise biobased feedstocks and develop more sustainable chemistry poses new challenges in catalysis. A synthetically useful catalytic conversion is ethenolysis, a cross metathesis reaction with ethylene. In this Review, the state of the art of ethenolysis in biobased chemistry was extensively examined using methyl oleate as a model compound for fatty acids. Allied to this, the ethenolysis of fatty acid, polymers and more challenging substrates are reviewed. To determine the limiting factors for the application of ethenolysis on biomass, the influence of reaction parameters were investigated and the bottlenecks for reaching high turnover numbers identified.
A simple, one-step mechanochemical procedure for immobilisation of homogeneous metathesis catalysts in metal-organic frameworks was developed. Grinding MIL-101-NH (Al) with a Hoveyda-Grubbs second-generation catalyst resulted in a heterogeneous catalyst that is active for metathesis and one of the most stable immobilised metathesis catalysts. During the mechanochemical immobilisation the MIL-101-NH (Al) structure was partially converted to MIL-53-NH (Al). The Hoveyda-Grubbs catalyst entrapped in MIL-101-NH (Al) is responsible for the observed catalytic activity. The developed synthetic procedure was also successful for the immobilisation of a Zhan catalyst.
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