NOVEL AMPHIPHILIC DIPHOSPHINES - SYNTHESIS, RHODIUM COMPLEXES, USE INHYDROFORMYLATION AND RHODIUM RECYCLING

For the rhodium-catalysed hydroformylation of higher alkenes the novel amphiphilic diphosphines is[phenyl(3-pyridyl)phosphinomethyl]-1,1'-bi phenyl (L(1)), 2,2'-bis(diphenylphosphinomethyl)-3,3'-bipyridine (L(2) ), [phenyl(3-pyridyl)phosphinomethyl]-3,3'-bipyridine (L(3)) and ethyl )-phenyl]phenylphosphinomethyl}-1,1'-biphenyl (L(4)) have been synthes ised. With oct-1-ene (80 degrees C, 20 bar CO-H-2, toluene), high norm al:branded ratios (up to 51:1) were found with 6-8% of isomerised octe nes. The diphosphines L(1)-L(3) gave rhodium catalysts up to twice as active as those derived from 2,2'-bis(diphenylphosphinomethyl)-1,1'-bi phenyl (bisbi). The rate of hydroformylation using L(1)-L(4) was first order and approximately first order respectively in the rhodium and o ct-1-ene concentration; the order in CO pressure was negative and that in H-2 pressure slightly negative. For L(1) the influence of the L:Rh ratio, temperature and substrate were investigated. Phosphorus-31 and H-1 NMR studies showed that the diphosphines (L-L) form [RhH(CO)(PPh( 3))(L-L)] and [RhH(CO)(2)(L-L)] complexes, analogously to bisbi. The f ormation of P-N chelates was not observed. The pH-dependent distributi on characteristics of the free diphosphines have been determined; L(3) and L(4) were quantitatively extracted from an Et(2)O solution into a H2SO4 solution of pH 2. When L(4) was used, rhodium and the excess of L(4) Were extracted into an acidic aqueous phase at pH 5, allowing se paration of the aldehydes, and re-extracted into fresh toluene after n eutralisation of the aqueous phase by NaHCO3. Inductively coupled plas ma atomic emission spectroscopy established a rhodium recovery up to 9 2%. Pressurising the recovered rhodium and excess of phosphine to 20 b ar CO-H-2 at 80 degrees C resulted in regeneration of the original cat alytically active species. A retention of catalytic activity of 72% wa s achieved. Diphosphines L(1)-L(3) proved inappropriate for rhodium-re cycling experiments. Extraction into an acidic aqueous phase was effec tive, but neutralisation of the acidic phase resulted in the formation of rhodium species which cannot be extracted from the aqueous layer.