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Silica immobilised palladium phosphine complexes as recyclable, regioselective catalysts for the allylic alkylation

✍ Scribed by Albertus J Sandee; Dragana Dimitrijevic; Richard J van Haaren; Joost N.H Reek; Paul C.J Kamer; Piet W.N.M van Leeuwen


Publisher
Elsevier Science
Year
2002
Tongue
English
Weight
128 KB
Volume
182-183
Category
Article
ISSN
1381-1169

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✦ Synopsis


The covalent immobilisation of palladium phosphine complexes on silica is demonstrated to be a viable method for the recovery of allylic alkylation catalysts. Both bidentate and monodentate phosphine ligands form stable palladium catalysts that could be recycled without catalyst deterioration and metal leaching. The regioselectivity of the immobilised catalyst for the alkylated products showed the same trend as the homogeneous analogues; in the alkylation of 3-methyl-but-2-enyl trifluoroacetate with sodium diethyl 2-methylmalonate we observed an increase in selectivity for the branched product from 11.6 to 58.3% on increasing the P-Pd-P bite angle from 93 to 108 β€’ . The morphology of the silica support did not have impact on the catalyst performance as amorphous silica and MCM-41 supported Pd(1) gave a similar product distribution in the alkylation of 3-methyl-but-2-enyl trifluoroacetate with sodium diethyl 2-methylmalonate (42% linear (E) alkylated product and 58% branched alkylated product). We observed that a pre-modification of the silica surface using dichlorodimethylsilane was crucial for the recycling properties of the catalyst system. Using non-modified silica both the conversion (from 24 to 19%) and the regioselectivity (from 43 to 19% for the branched alkylation product) dropped in four consecutive catalyst runs using Pd(1) . The modified systems yielded high conversions (68-64%) and increased regioselectivies for the branched alkylation product (58-57%) in four consecutive catalytic runs.


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