Redox chemistry of Pd 2+, Pt 2+, Rh 3+–TPPTS systems in water: pH influence on the preparation of low valent TPPTS complexes

Abstract

The redox process of the water-soluble systems: TPPTS–Pd(OAc) 2, PdSO 4, PtCl 2, Rh 2(SO 4) 3, and RhCl 3, have been investigated at room temperature by 31 P -NMR spectroscopy, polarography and pH measurement. (TPPTS: 3,3′,3″-phosphinidynetris(benzenesulfonic acid) trisodium salt, or the usual name: tris( m-sulfophenyl)phosphine trisodium salt). For a particular given value of pH, controlled by NaOH addition, except for Rh 2(SO 4) 3 which leads to a Rh(OH) 3 precipitate, every system evolved very quickly, producing quantitatively OTPPTS (TPPTS oxide) and the metallic complexes with TPPTS in a reduced state: Pd(TPPTS) n at pH>5; Pt(TPPTS) n+1 at pH>7; [ + Rh (TPPTS) n ] at 7<pH<13, n ranging between 2 and 3. With Pd(II) and Pt(II) which are complexed in the oxidized state, the hydroxide ion intervenes probably to accelerate the disproportionation of an hydroxo species such as MOH(TPPTS) n + into OTPPTS and a low valence state metal complex: OH −+HOM(TPPTS) n +→M(TPPTS) n−1 +OTPPTS+H 2O. The fact that TPPTS complexation by Rh(III) is not observed, implies that the different hydroxochloro Rh(III) species react directly with TPPTS to produce OTPPTS and Rh(I) which is subsequently complexed by TPPTS.