Triphenylphosphine, sulfonated hydroformylation

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 latest development in industrial alkene hydroformylation is the introduction by Rurhchemie of water-soluble sulfonated triphenylphosphine ligands.94 Hydroformylation is carried out in an aqueous biphasic system in the presence of Rh(I) and the trisodium salt of tris(m-sulfophenyl)phosphine (TPPTN). High butyraldehyde selectivity (95%) and simple product separation make this process more economical than previous technologies. 

Kuntz subsequently showed that the RhCl (tppts) 3 catalyzed the hydroformylation of propylene in an aqueous biphasic system [29]. These results were further developed, in collaboration with Ruhrchemie, to become what is known as the Ruhrchemie/Rhone-Poulenc two-phase process for the hydroformylation of propylene to n-butanal [18, 19, 22, 30]. Ruhrchemie developed a method for the large scale production of tppts by sulfonation of triphenylphosphine with 30% oleum at 20 °C for 24 h. The product is obtained in 95% purity by dilution with water, extraction with a water insoluble amine, such as tri(isooctylamine), and pH-controlled re-extraction of the sodium salt of tppts into water with a 5% aqueous solution of NaOH. The first commercial plant came on stream in 1984, with a capacity of 100000 tons per annum of butanal. Today the capacity is ca. 400000 tpa and a cumulative production of millions of tons. Typical reaction conditions are T=120°C, P=50bar, CO/H2 = 1.01, tppts/Rh = 50-100, [Rh] = 10-1000 ppm. The RhH(CO) (tppts)3 catalyst is prepared in situ from e.g. rhodium 2-ethylhexanoate and tppts in water. 

The fact that water-soluble sulfonated phosphines may combine the properties of a ligand and a surfactant in the same molecule was first mentioned in 1978 by Wilkinson etal. [11] in their study of the hydroformylation of 1-hexene using rhodium and ruthenium catalysts modified with TPPMS (triphenylphosphine mono-... 

Cuprous chloride tends to form water-soluble complexes with lower olefins and acts as an IPTC catalyst, e.g., in the two-phase hydrolysis of alkyl chlorides to alcohols with sodium carboxylate solution [10,151] and in the Prins reactions between 1-alkenes and aqueous formaldehyde in the presence of HCl to form 1,3-glycols [10]. Similarly, water-soluble rhodium-based catalysts (4-diphenylphosphinobenzoic acid and tri-Cs-io-alkylmethylam-monium chlorides) were used as IPTC catalysts for the hydroformylation of hexene, dodecene, and hexadecene to produce aldehydes for the fine chemicals market [152]. Palladium diphenyl(potassium sulfonatobenzyl)phosphine and its oxide complexes catalyzed the IPTC dehalogenation reactions of allyl and benzyl halides [153]. Allylic substrates such as cinnamyl ethyl carbonate and nucleophiles such as ethyl acetoactate and acetyl acetone catalyzed by a water-soluble bis(dibenzylideneacetone)palladium or palladium complex of sulfonated triphenylphosphine gave regio- and stereo-specific alkylation products in quantitative yields [154]. Ito et al. used a self-assembled nanocage as an IPTC catalyst for the Wacker oxidation of styrene catalyzed by (en)Pd(N03) [155]. 

The low solubility of most organometaUic catalysts in COj means that in ideal cases no modification catalyst is required, provided it is suffidenfly soluble in the IL. This was foimd to be the case for the hydrovinylation system which employed a nickel-based chiral catalyst first reported by Wilke and co-workers [23], In the case of the hydroformylation system, however, the activity was foimd to be highest when using [Rh(acac)(CO)2] combined with a sulfonated triphenylphosphine analogue that had an imidazoHum cation as its counterion. In practice it is likely that neutral catalysts may require charged ligands, while those which are themselves charged can be used unmodified. 

One interesting design of macromolecular soluble metal complexes is binding of a rhodium complex with sulfonated triphenylphosphine to a soluble polyelectrolyte, polydiallyldimethylammonium tetrakis(3,5-bis(trifluorome-thyl)phenyl borate. In this ease, the content of phosphine groups enables us to control the catalyst solubility in methanol at high content of the phosphine counter ion, the polymer is insoluble and if the ratio of tetraalkylammonium groups to phosphine groups is 4 1 and 10 1, the polymer is soluble in methanol and is an active catalyst of 1-hexene hydroformylation. The catalyst was separated by ultrafiltration [177]. 

Schweb and Mecking have reported one of the first examples of noncovalent anchoring of catalysts to soluble polymeric supports in 2001. This noncovalently anchored catalyst featured phosphine ligands that were bound by multiple sulfonate groups to soluble polyelectrolytes using electrostatic interactions. The catalyst system was employed in the hydroformylation of 1-hexene and exhibited typical selectivity for a bis-triphenylphosphine-bound rhodium catalyst. The complex was readily recovered and recycled by ultrafiltration. Independently, Reek et al. described similar systems, but these systems made use of a soluble... 

Besides acids and esters, the corresponding unsaturated long-chain alcohols have also been subjected to the addition of syngas [52]. For example, the hydroformylation of oleic alcohol, in which the substrates can be prepared by heterogeneous hydrogenation of oleic acid esters [53] using a sulfonated triphenylphosphine as a ligand under neat conditions, has been described in a patent of Ruhrchemie (Scheme 6.96) [54]. 

Much research has been devoted to water-soluble sulfonated phosphines and, in particular, the well-known TPPTS (triphenylphosphine tris-sulfonated sodium salt) ligand used in propene hydroformylation on an industrial scale by Ruhrchemie/ Rhone-Poulenc since 1982 (Figure 6.8) [9, 10]. 

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