RHODIUM-CATALYZED HYDROFORMYLATION OF HIGHER ALKENES USING AMPHIPHILIC LIGANDS .2.

The performance of a new rhodium recycling system is described using a series of amphiphilic ligands: Ph(2)ArP (Ar = 3-hydroxyphenyl, 4-carb oxyphenyl), Ph(n)Ar(3-n)P (Ar = 4-PhCH(2)X, X=NEt(2), NMePh, NPh(2); n = 1-2) and Ph(n)Ar(3-n)P (Ar = 3-pyridyl, 4-pyridyl; n = 1-2). The co rresponding rhodium complexes are active in the hydroformylation of oc t-1-ene and can be separated from the product aldehydes by acidic or b asic extraction into water. After neutralisation of the aqueous phase the rhodium phosphine species can be extracted into a new batch of oct -1-ene, with toluene as organic solvent. The pH-depending distribution characteristics of the free ligands have been determined. PhAr(2)P wi th Ar = 4-PhCH(2)NEt(2) and Ar = 3-pyridyl were completely extracted f rom a solution in Et(2)O or toluene into a H2SO4-solution of pH 3 and 2, respectively, Recycling experiments with the former ligand demonstr ated that the catalytically active rhodium hydrides decompose during t he acidic extraction step. The structure of the recovered rhodium comp lexes could not be elucidated by NMR- and IR-analysis. Rhodium measure ments by ICP-AES established that rhodium was quantitatively recycled. Pressurising the recovered rhodium and excess ligand to 20 bar syngas at 80 degrees C resulted in regeneration of the original, catalytical ly active species. A retention of catalytic activity up to 87% was ach ieved.