Rhodium-catalyzed hydroformylation water-soluble catalysts

Only limited data are available for the kinetics of oxo synthesis with the water-soluble catalyst HRh(CO)(TPPTS)3. The hydroformylation of 1-octene was studied in a two-phase system in presence of ethanol as a co-solvent to enhance the solubility of the olefin in the aqueous phase [115]. A rate expression was developed which was nearly identical to that of the homogeneous system, the exception being a slight correction for low hydrogen partial pressures. The lack of data is obvious and surprising at this time, when the Ruhrchemie/ Rhone-Pou-lenc process has been in operation for more than ten years [116]. Other kinetic studies on rhodium-catalyzed hydroformylation have been published, too. They involve rhodium catalysts such as [Rh(nbd)Cl]2 (nbd = norbomadiene) [117] or [Rh(SBu )(CO)P(OMe)3]2 [118], or phosphites as ligands [119, 120]. 

Two new phosphines, tris[p-(10-phenyldecyl)phenyl]phosphine and 2,2 -bis di [p-(10-phenyldecyl)phenylphosphinomethyl]-l,T-biphenyl were successfully synthesized and sulfonated in H2S04. The resulting water soluble surface active phosphines were applied to the rhodium catalyzed hydroformylation of higher alkenes. It is found that these two ligands are not only excellent for octene hydroformylation, but catalyze tetradecene hydroformylation under biphasic conditions as well. Rates and selectivities are superior to TPPTS-modified rhodium catalysts under the same reaction conditions [68]. 

The thermal instability of rhodium-based hydroformylation catalysts has already been overcome commercially in the Ruhrchemie/Rhone-Poulenc process for propene hydroformylation in which the sodium salt of a sulfonated triphe-nylphosphine ligand (TPPTS, la) is used to solubilize the catalyst in the aqueous phase. In this process, the second phase is toluene and the reaction is carried out as a batch process with rapid stirring to intimately mix the two immiscible phases. After reaction, the system is allowed to separate and the organic phase is simply decanted from the aqueous catalyst phase. Both water-soluble polymers and PAMAM dendrimers have been reported as supports for rhodium-catalyzed hydroformylation under aqueous biphase conditions, but reactivities and regioselec-tivities were only comparable to or worse than those obtained with the reference TPPTS ligand. The aqueous biphase approach has found limited application for the hydroformylation of longer-chain alkenes, because of their very low solubility in water leading to prohibitively slow reaction rates, but there have been a variety of approaches directed at the solution of this problem. 

Finally, water-soluble phosphorylated BlNAPs were tested as ligands in aqueous biphasic rhodium-catalyzed hydroformylation of vinyl acetate. Compared with catalysts prepared with the parent ligand in a homogeneous medium, the chemo-, regio- and enantioselectivities were markedly lower [24]. 

Hydroformylation of Aliphatic Olefins In 1997, Herrmann and coworkers [25] were the first to use NHCs and imidazohum salts, respectively, as hgands or preligands in rhodium-catalyzed hydroformylation. The isolated NHC-rhodium complexes 1 and 2 (Figure 2.55) and the complexes prepared in situ from the water-soluble imidazolium salts 3a-c and rhodium(lll)acetate were tested in the homogeneous and biphasic hydroformylation of propene. The catalyst derived from 1 produced >99% yield of isomeric butanals (CO/H2 = 1 1,10 MPa S/C = 100 000 1, toluene, 60 h). In the biphasic system, after 20 h of reaction time and S/C = 10000 1 in water, rhodium catalysts derived from 2 or based on hgands 3a-c allowed up... 

Biphasic catalysis in the presence of water-soluble catalysts has been the most significant development in recent years. After the report of Kuntz on the synthesis of sulfonated triarylphosphine TPPTS (Figure 14.1) and its successful industrial application in Rh-catalyzed hydroformylation of propene, great attention has been focused on the scientific study and industrial application of water-soluble catalysts, especially on water-soluble phosphines [6, 7], phosphites, and other phosphide compounds as well as their rhodium complexes [8]. Among them, TPPTS is the most widely studied and applied. Other important phosphine hgands will he introduced later. 

The mechanism of olefin hydroformylation catalyzed by rhodium complexes has been extensively studied. For TPP as a ligand, it corresponds to Wilkinson s dissociative mechanism, which involves the four-coordinated active intermediate HRh(CO)L2 (L = TPP, Figure 14.2). Coordination of olefin with HRh(CO)L2 yields the 7t-complex 2. The insertion of coordinated olefin to the Rh-H bond leads to the formation of alkyl complexes 3a or 3b, respectively, via the anti-Markovnikov or the Markovnikov path. Subsequently, the alkyl migration to the CO affords the acyl complexes 4a or 4b, which leads to linear or branched aldehyde and HRh(CO)L2 via hydrogenolysis, eventually. The water-soluble catalyst HRh(CO)(TPPTS)3 is considered to react according to the dissociative mechanism [10]. However, the reaction occurs at the liquid phase or the gaseous-Hquid interface [11], and the activity and selectivity are remarkably different from those... 

An important development in the past 15 years in hydroformylation technology was the introduction of biphasic homogeneous catalysis. Kuntz (62) expressed the basic idea of a new generation of water-soluble oxo catalysts with triphenylphosphane trisulfonate (tppts as the sodium salt) as a ligand for a rhodium-complex-catalyzed hydroformylation process. Ruhrchemie AG adapted the idea on the basis of research done at Rhone-Poulenc and developed it into an industrially viable process, which was... 

More extensive use has been made of TPPTS than of TPPMS as a ligand for preparing water-soluble homogeneous catalysts. The major reason for this is that the presence of three sulfonate groups on TPPTS causes it to have a greater solubility in aqueous solution than does TPPMS. The principal application of TPPTS has been as a ligand for rhodium in catalyzed hydroformylation reactions. In the hydroformylation of propene with such catalyst systems, the reaction conditions use an equimolar mixture of CO and H2 at 40-bar pressure and 125°C in an aqueous solution of pH 6.0... 

Hydroformylation or oxosynthesis is a well-known homogeneous, transition metal catalyzed reaction which has known considerable and continuous development since its discovery by Otto Roelen in the laboratories of Ruhrchemie AG in 1938 [1], This reaction, which can be considered as the addition of a formyl group and hydrogen to a double bond, has been successfully applied in the industrial context by using two basic processes the homogeneous process where the rhodium or cobalt catalyst and the substrate are in the same phase (Shell, UCC, BASF, RCH processes) [2] and the aqueous/organic biphasic process where the water-soluble rhodium catalyst and the organic compounds are in two different phases (Ruhr-chemie/Rhone-Poulenc process) [3]. 

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]. 

---