A water-soluble phosphite derived from sulfonated calix[4]arene. The remarkable stability of its rhodium complexes and two phase hydroformylation studies

Abstract

The reaction of tetrasulfonated calix[4]arene (trioctylammonium salt) with P(NMe₂)₃ followed by treatment with gaseous NMe₂H gave a zwitterionic six-coordinate phosphorus(V) species 1 containing a P(H)(NHMe₂) group which can be stored for months without decomposition. In water, 1 loses NHMe₂ and rearranges to form the water soluble phosphite L_cc. Phosphite L_cc has a half-life in water of ca. 5 h decomposing to H₃PO₃ and free tetrasulfonated calix[4]arene. Compound 1 serves as a convenient precursor to L_cc and complexes of L_cc are formed by dissolving 1 in water in the presence of labile metal complexes. The products have been identified by comparison of their ³¹P NMR data with well established analogues of calix[4]arene derived phosphites. In this way the water soluble complexes [Rh(acac)(CO)(L_cc)₂] (2c) [Rh₂Cl₂(CO)₂(L_cc)₂] (3c), [Pt₂Cl₄(L_cc)₂] (4c) and [PtCl₂(L_cc)₂] have been tentatively identified. The rhodium complex 3c has a half-life in water of 4 months. Two-phase (water/toluene) hydroformylation of 2-methylpentenoate with 2c as a catalyst has been investigated and the results compared with the same reaction in toluene with lipophilic analogues of 2c. Under mild conditions, with 2ccatalyst, branched aldehydes are the only products of hydroformylation and one of the branched aldehydes is selectively hydrogenated to give the lactone derivative.