A WATER-SOLUBLE DIPHOSPHINE LIGAND WITH A LARGE NATURAL BITE ANGLE FOR 2-PHASE HYDROFORMYLATION OF ALKENES

The concept of a large 'natural' bite angle in chelating diphosphines has been extended to two-phase alkene hydroformylation by the use of a water-soluble diphosphine based on a xanthene-type backbone. The rece ntly developed diphosphine Xantphos was modified with water-soluble gr oups by controlled sulfonation in fuming sulfuric acid to form a)-4,5- bis(diphenylphosphino)-9,9-dimethylxanthene (2,7-bis(SO3Na)-Xantphos) exclusively. The application of this ligand in the two-phase rhodium-c atalyzed hydroformylation of alkenes led to the selective formation of linear aldehydes. Some data are reported on the hydroformylation of p ropene, hex-l-ene and 4-styrenesulfonate. Recycling experiments showed the catalyst to be active up to five cycles. For comparison, the two- phase catalytic results are also given with TPPTS as the ligand. Furth ermore, the coordination behaviour of the in situ formed catalytic spe cies HRh(2,7-bis(SO3Na)-Xantphos)(CO)(2) was studied by high-pressure NMR spectroscopy which indeed showed the desired bis-equatorial coordi nation of the ligand to the rhodium center. (C) 1998 Elsevier Science B.V. All rights reserved.