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Rhodium Complexes Based on Phosphorus Diamide Ligands:  Catalyst Structure versus Activity and Selectivity in the Hydroformylation of Alkenes

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journal contribution
posted on 23.05.2000, 00:00 by Saskia C. van der Slot, Paul C. J. Kamer, Piet W. N. M. van Leeuwen, Jan Fraanje, Kees Goubitz, Martin Lutz, Anthony L. Spek
The rhodium-catalyzed hydroformylation reaction of 1-octene with phosphorus diamide ligands has been investigated. Four monodentate phosphorus diamide ligands and six bidentate phosphorus diamide ligands derived from a 1,3,5-trisubstituted biuret structure have been synthesized. These types of ligands combine steric bulk with π-acidity. The rhodium complexes formed under CO/H2 have been characterized by high-pressure spectroscopic techniques. Spectroscopic experiments revealed that the monodentate ligands form mixtures of HRhL2(CO)2 and HRhL(CO)3. The ratio HRhL2(CO)2:HRhL(CO)3 depends on the ligand concentration and its bulkiness. The bidentate ligands form stable, well-defined catalysts with the structure HRhL∩L(CO)2 under hydroformylation conditions. Both monodentate and bidentate ligands have been tested in the hydroformylation reaction of 1-octene. The monodentate ligands form very active catalysts, but the linear-to-branched ratio of the product is low. The bidentate ligands show improved selectivity compared to the monodentate ligands and an activity that is only slightly lower.

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