Trisulfonated phosphine ligands

Triphenylphosphine and trisulfonated triphenylphosphine continue to be the most important monodentate phosphine ligands in rhodium-catalyzed hydroformylation, both in industrial processes and in applications in organic syntheses. The precursor introduced by Wilkinson was the complex RhH(PPh3)3CO, 16 with structure 3,... 

Replacement of tppts by the fluoro substituted sulfonated ligand 4 [Table 2 94% (n=l) and 6% (n=0)] in the rhodium-catalysed hydroformylation of 1-hexene in a two phase system increased the selectivity to linear aldehyde n-heptanal from 86% to 93% at the low P/Rh molar ratio of 7.5/1.75,76 The Rh/4 catalyst was quantitatively recovered after the reaction by simple decantation.75,76 The moderate increase of the n/i ratio is of interest when one considers that ligand 4 is mainly present as the disulfonated species (94%) compared to the trisulfonated compound tppts and that tris(4-fluorophenyl)phosphine is less basic (pKa=1.97) than triphenylphosphine (pKa=2.73).376 In rhodium-catalysed hydroformylation reactions in organic solvents it is known that electron withdrawing substituents, which increase the -acidity of the ligand, give rise to an increase in the n/i ratio.377 379... 

The commercial success of rhodium-trisulfonated triphenylphosphine (TPPTS) catalysts1 has prompted considerable interest in TPPTS and other water-soluble ligands.2 The potential for new applications for the synthesis of both bulk and fine chemicals in water has led to methods for the preparation of a wide variety of sulfonated phosphines including chiral phosphines3 and... 

Following the recommendations of Manassen [18] the history of biphasic hydroformylation began with work on various water-soluble ligands (Table 1). After this preparatory work on various aspects [30], Kuntz [22, 199] expressed the basic idea of a new generation of water-soluble oxo catalysts with triphenyl-phosphine trisulfonate (TPPT S, as the Na salt, as compared with TPPMS and TPPDS, the mono- and disulfonate) as ligands for a Rh-based oxo process, mainly for the hydroformylation of lower olefins such as propene (eq. (5)). 

Roughly at the same time (in contradiction to a misleading publication by Papado-gianakis [2]) and parallel to work done by Joo [3] and others [4], one of us (EK, then at Rhone-Poulenc) devoted time and effort to starting practical work on biphasic catalysis with organometallic catalysts (especially hydroformylation), developing the biphasic principle and the current well-known standard ligand triphenyl-phosphine trisulfonate (TPPTS, cf. Section 3.2.1). 

A very important process with the solvent water is the hydroformylation of propene to butyraldehydes, known as the Ruhrchemie/Rhone-Poulenc process. The reaction is catalyzed by a rhodium complex containing the water-soluble ligand triphenyl-phosphine trisulfonate (TPPTS) (see Section Lower Alkenes [6-11]). 

Commercially, the aqueous-phase concept was firstly applied in Ruhrchemie/Rhone-Poulenc s (RCH/RP) process (for the fundamentals, see Section 2.4.1.1). In several units the RCH/RP process has been converting propene to n-butyraldehyde and isobutyraldehyde (or butenes to valeraldehydes) since 1984 in the presence of HRh(CO)(TPPTS)3 (with TPPTS = m-trisulfonated triphenylphosphine or tris-(sodium-fn-sulfonatophenyl)phosphine as water-soluble ligand) according to Eq. (1). The output of the units mentioned is approximately890 000 tpy, which corresponds to roughly 13% of the world s total production. 

Sulfonated triphenylphosphine [TPPTS (triphenylphosphine, m-trisulfonated) tri(m-sulfophenyl)phosphine] (II-l) and monosulfonated triphenylphosphine [TP-PMS (triphenylphosphine, monosulfonated) 3-(diphenylphosphino)benzenesul-fonic acid] (II-2) are commercially available ligands and their sodium salts are water-soluble [15]. The Na salt of the ligand TPPTS is very soluble and may be too soluble in water, hence moderately soluble TPPMS is preferred. Another water-soluble phosphine is 2-(diphenylphosphinoethyl)trimethyl ammonium halide (II-11) [16]. A number of other water-soluble phosphines are now known (Table 1.2). Pd complexes, coordinated by these phosphines, are soluble in water, and Pd-catalyzed reactions can be carried out in water, which is said to have an accelerating effect in some catalytic reactions. 

For propylene hydroformylation with Rh catalyst, PPh used to be the ligand of choice. Today in Rh-based technology, water-soluble 5.19 is used as the ligand. This ligand, triphenyl phosphine trisulfonated, is abbreviated as TPPTS. Ligand 5.22 is the monosulfonated analogue of 5.19 and is called TPPMS (triphenyl phosphine monosulfonated). The solubility properties of 5.19 and 5.22 in biphasic systems are somewhat different. 

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