Rhodium based hydroformylation catalyst

For a more detailed outline of the various cobalt- and rhodium-based hydroformylation catalysts and for additional related references, see G. O. Spessard and G. L. Miessler, Organometallic Chemistry, Prentice Hall, Upper Saddle River, NJ, 1997, pp. 257-265. 

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. 

During the course of studies [27, 30, 31] on a range of different phosphines and phosphites for solubilizing rhodium-based hydroformylation catalysts in SCCO2, it... 

Ligand (136), an analog of PPh3 with amphiphilic character, was used for making [Rh(CO) (136)(acac)]. The rhodium-based hydroformylation of 1-hexene using catalysts formed in situ... 

The use of catalytic SILP materials has been reviewed recently [10] covering Friedel-Crafts reactions [33-37], hydroformylations (Rh-catalyzed) [38], hydrogenation (Rh-catalyzed) [39,40], Heck reactions (Pd-catalyzed) [41], and hydroaminations (Rh-, Pd-, and Zn-catalyzed) [42]. Since then, the SILP concept has been extended to additional catalytic reactions and alternative support materials. In this paper we will present results from continuous, fixed-bed carbonylation and hydroformylation reactions using rhodium-based SILP catalysts as reaction examples demonstrating the advantages of the SILP technology for bulk chemical production. 

Three commercial homogeneous catalytic processes for the hydroformyla-tion reaction deserve a comparative study. Two of these involve the use of cobalt complexes as catalysts. In the old process a cobalt salt was used. In the modihed current version, a cobalt salt plus a tertiary phosphine are used as the catalyst precursors. The third process uses a rhodium salt with a tertiary phosphine as the catalyst precursor. Ruhrchemie/Rhone-Poulenc, Mitsubishi-Kasei, Union Carbide, and Celanese use the rhodium-based hydroformylation process. The phosphine-modihed cobalt-based system was developed by Shell specih-cally for linear alcohol synthesis (see Section 7.4.1). The old unmodihed cobalt process is of interest mainly for comparison. Some of the process parameters are compared in Table 5.1. 

Rhodium is an expensive metal, and the commercial viability of the rhodium-based hydroformylation process depends crucially on the efficiency of the catalyst recovery process. In the past this has been achieved either by a complicated recycle process or more commonly by energy-requiring distillation. A major advancement in catalyst recovery in recent years has been the introduc-... 

Rhodium-based homogeneous catalysts have found widespread application in a variety of processes, including hydroformylation of alkenes, methanol carbonylation to acetic acid (the Monsanto process), and various hydrogenation and C-H activation reactions. 

Currently, a wide range of methods are available to generate active rhodium hydroformylation catalysts from catalyst precursors based on rhodium in oxidation states of O-III. Because of the almost unmanageable amount of protocols concerning the rhodium-based hydroformylation in the literature, a clear conclusion about the efficiency and duration of catalyst formation processes prior to the hydroformylation is hard to draw. A deeper understanding of these processes occurring prior to the hydroformylation would be of interest in order to distinguish between different catalyst precursors. 

Because of the technical success of rhodium based hydroformylations, it is understandable that since the 1970s the vast majority of academic and industrial investigations in this area dealt with the development of new rhodium catalysts. However, the worldwide demand of rhodium for chemical and technical processes and its enormous price stimulate the search for alternative transition-metal catalysts up to now [1]. A particular focus was given to ruthenium [2]. 

Interestingly, not only long-chain olefins were meanwhile submitted to SILP systems. Bell and coworkers [113] investigated the hydroformylation of propene using [BMIM] [OctSO J and a Rh(Sulfoxantphos) catalyst. The activity and stability of the rhodium-based SILP catalyst were highly sensitive to its formulation. Dehydration ofthe support at 750 C or removal ofthe silanol groups reduced the... 

The switch from the conventional cobalt complex catalyst to a new rhodium-based catalyst represents a technical advance for producing aldehydes by olefin hydroformylation with CO, ie, by the oxo process (qv) (82). A 200 t/yr CSTR pilot plant provided scale-up data for the first industrial,... 

The catalysts used in hydroformylation are typically organometallic complexes. Cobalt-based catalysts dominated hydroformylation until 1970s thereafter rhodium-based catalysts were commerciahzed. Synthesized aldehydes are typical intermediates for chemical industry [5]. A typical hydroformylation catalyst is modified with a ligand, e.g., tiiphenylphoshine. In recent years, a lot of effort has been put on the ligand chemistry in order to find new ligands for tailored processes [7-9]. In the present study, phosphine-based rhodium catalysts were used for hydroformylation of 1-butene. Despite intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and kinetics are not in the most cases clear. Both associative and dissociative mechanisms have been proposed [5-6]. The discrepancies in mechanistic speculations have also led to a variety of rate equations for hydroformylation processes. 

A lot of research has been published on hydroformylation of alkenes, but the vast majority of the effort has been focused on the chemistry of various metal-ligand systems. Quantitative kinetic studies including modeling of rates and selectivities are much more scarce. In this work, we present the approach to modeling of hydroformylation kinetics and gas-solubility. Hydroformylation of 1-butene with a rhodium-based catalyst was selected as a case study. 

A new chiral auxiliary based on a camphor-derived 8-lactol has been developed for the stereoselective alkylation of glycine enolate in order to give enantiomerically pure a-amino acid derivatives. As a key step for the synthesis of this useful auxiliary has served the rc-selective hydroformylation of a homoallylic alcohol employing the rhodium(I)/XANTPHOS catalyst (Scheme 11) [56]. 

Although early catalysts were based on cobalt, nowadays, rhodium catalysts are preferred because they require lower pressure and afford higher chemo- and regioselectivity [1,2]. In recent years, extensive research into the production of only linear aldehydes has provided impressive results. The application of phosphines with a wide bite angle in the rhodium catalyzed hydroformylation of terminal alkenes enable the regioselectivity to be almost totally controlled [3]. Branched selective hydroformylation, al-... 

These results promote a potential use of cobalt catalysts instead of expensive rhodium-based catalysts for the hydroformylation in SCCO2 [16,17,209, 210]. Although the main goal of this study was to demonstrate catalyst recycling, it must be noted that the catalytic performances have been obtained at process parameters and imder conditions that were far from being optimized. 

Table 8.5 Mono- and bimetallic cobalt- and rhodium-based catalysts prepared from carbonyl compounds and used in the CO hydrogenation and/or hydroformylation reactions.

In 1995, nearly 80% of all oxo products and over 90% of the propene hydroformylation products were produced using rhodium-based catalysts.48... 

Figure 1.13 Generation of rhodium-based supramolecularcatalysts by assembly of pyridine/hydroxypyridine pairs (a) Self-assembly modes of pyridine-based phosphines, (b) Alkene hydroformylation with supramolecular rhodium-diphosphine catalysts (c) CAChe minimized 3D structure ofthe rhodium-diphosphine complex (other ligands from the metal omitted for clarity).

---