NOVEL AMPHIPHILIC DIPHOSPHINES - SYNTHESIS, X-RAY STRUCTURE, RHODIUM COMPLEXES, USE IN HYDROFORMYLATION, AND RHODIUM RECYCLING

Three novel amphiphilic diphosphines have been synthesized: bis[2-(phe nyl(3-pyridyl)phosphino)ethyl] ether (POPpy) and hylamino)methyl)pheny l)phenylphosphino)ethyl]ether (POPam), based on bis[2-(diphenylphosphi no)ethyl]ether (POP), and no)methyl)phenyl)phosphino]-10,10-dimethylxa nthene (xantham), based on 4,6-bis(diphenylphosphino)-10,10-dimethylxa nthene (Xantphos). The crystal structure of xantham has been determine d. Solution structures of rhodium xantham complexes have been studied using NMR and IR spectroscopy. When POPam is used in the hydroformylat ion of oct-1-ene, a linear/branched ratio (l/b) of 7.3 is achieved (88 % nonanal) without isomerization to oct-2-ene. The use of POPpy result s in an activity that is twice as high, a higher l/b-ratio of 9, and 0 .7% isomerization. When xantham is used in the hydroformylation of hex -1-ene, oct-1-ene, and dodec-1-ene (80 degrees C, 20 bar of syngas, to luene), l/b-ratios of 50 have been achieved (94% nonanal) together wit h 4% of isomerized octenes. The pH-dependent distribution characterist ics of the free Ligands have been determined, and it is shown that POP py, POPam, and xantham can be extracted for 40% from a Et2O solution i nto an aqueous solution of H2SO4 at pH values of, respectively, 2.5, 5 , and 5. Rhodium recycling experiments using POPam and xantham show th at rhodium can be extracted into an aqueous layer at pH 5-5.5 for more than 99.95%, as determined by ICP-AES analysis, which allows complete separation of the product aldehydes and catalyst. After neutralizatio n of the aqueous phase containing protonated POPam with an aqueous sol ution of NaHCO3, only 65% of the rhodium can be re-extracted into fres h toluene. In the case of xantham, 98% of the rhodium is re-extracted. Pressurizing the recovered rhodium and excess xantham to 20 bar at 80 degrees C resulted in regeneration of the original active hydride com plex, as judged by the retention of activity of up to 86%. POPpy has p roved inappropriate for the recycling of rhodium.