Rhodium triphenylphosphine

Similar activation takes place in the carbonylation of dimethyl ether to methyl acetate in superacidic solution. Whereas acetic acid and acetates are made nearly exclusively using Wilkinson s rhodium catalyst, a sensitive system necessitating carefully controlled conditions and use of large amounts of the expensive rhodium triphenylphosphine complex, ready superacidic carbonylation of dimethyl ether has significant advantages. 

G-19 Dicarboxylic Acids. The C-19 dicarboxyhc acids are generally mixtures of isomers formed by the reaction of carbon monoxide on oleic acid. Since the reaction produces a mixture of isomers, no single chemical name can be used to describe them. Names that have been used include 2-nonyldecanedioic acid, 2-octylundecanedioic acid, l,8-(9)-heptadecanedicarboxyhc acid, and 9-(10)-carboxystearic acid. The name 9-(10)-carboxystearic acid can be used correctiy if the product is made with no double bond isomerization (rhodium triphenylphosphine catalyst system). 

Batch Experiments with Thermomorphic Systems. As a reference, we tested the hydroformylation of 1-octene in a completely homogeneous system using the same rhodium triphenylphosphine catalyst that is used for hydroformylation of lower aldehydes. This is sample R39 in Table 28.1, and gives us a baseline to compare the performance of our systems in terms of conversion and selectivity. To maintain consistency, we performed all the reactions at 100°C using the same amounts of reactants, catalysts and solvents. Under these conditions we only detected aldehyde products no alcohol or alkene isomers were formed. 

Most recently new applications for substrate-controlled branched-selective hydroformylation of alkenes substituted with inductively electron-with drawing substituents have emerged. A recent example is the hydroformylation of acrylamide with a standard rhodium/triphenylphosphine catalyst, which yields the branched aldehyde exclusively (Scheme 4) [40]. Reduction of the aldehyde function furnishes 3-hydroxy-2-methylpropionamide, which is an intermediate en route to methyl methacrylate. 

Batch continuous processing, in which part of the catalytic solution is removed to a low pressure distillation unit, on the other hand, has recently been commercialised [2-4]. Very little information is available in the public domain concerning this low pressure distillation process, but the main extra cost will be in generating the reduced pressure required for the distillation. The estimated vapour pressures at 110°C of various long chain linear aldehyde products that are commercially desirable are shown in Figure 9.1. This temperature has been chosen because this is the high temperature limit above which the rhodium triphenylphosphine complex starts to decompose. Any commercial process will require to operate the product distillation step at a pressure no higher than those shown for the individual aldehydes. 

Fig. 4. Dissociative mechanism for the rhodium-triphenylphosphine-catalyzed hydroformylation of olefins (24-27).

The reaction was stated to proceed by means of an associative mechanism, similar to the one proposed for the rhodium-triphenylphosphine system, with HPt(CO)(SnCl3)(PPh3) as the active intermediate. The high selectivity to linear aldehyde was attributed to steric requirements. The kinetic data led to the following general rate expression ... 

Incorporation of rhodium triphenylphosphine moieties into carboranes has led to HRh(C2B9Hn)(PPh3)2 complexes, which are formally hydri-dorhodium(III) dicarbollides and which catalyze olefin hydrogenation under mild conditions (527). Iridium and ruthenium analogs are also known, including complexes with carboranylphosphine ligands, e.g., HRuCl(PPh3)(l-P(CH3)2-l,2-C2B, Hn]2 (,527-530). 

Further information on the reaction intermediates is achieved by in situ NMR experiments. Because the signals in NMR spectra depend upon the concentration of the investigated species, a quantitative treatment is possible. Bianchini and coworkers investigated the hydroformylation of 1-hexene [62], using high-pressure NMR spectroscopy to evaluate the influence of synthesis gas on the equilibria of rhodium triphenylphosphine species. They were able to establish at least four resting states of rhodium (catalyst species that do not participate directly in the reaction). When synthesis gas interacted with... 

LPO process. Propene hydroformylation can be done with a rhodium triphenylphosphine catalyst giving a linearity ranging from 60 to 96 % depending on the phosphine concentration. At very high phosphine concentration the rate is low, but the linearity achieves its maximum value. The commercial process (Union Carbide Corporation, now Dow Chemicals) operates presumably around 30 bar, at 120 °C, at high triphenylphosphine concentrations, and linearities around 92%. The estimated turnover frequency is in the order of only 300 mol(product).mol 1 (Rh).h Low ligand... 

Mitsubishi Kasei introduced a process to manufacture isononyl alcohol, an important PVC (polyvinyl chloride) plasticizer, via the hydroformylation of octenes (a mixture of isomers produced by dimerization of the C4 cut of naphtha cracker or FCC processes).95 First a nonmodified rhodium complex exhibiting high activity and selectivity in the formation of the branched aldehyde is used. After the oxo reaction, before separation of the catalyst, triphenylphosphine is added to the reaction mixture and the recovered rhodium-triphenylphosphine is oxidized under controlled conditions. The resulting rhodium-triphenylphosphine oxide with an activity and selectivity similar to those of the original complex, is recycled and used again to produce isononanal. 

In the case of rhodium as a catalyst metal for the hydroformylation of methyl oleate, lower pressure and lower temperature have to be compared to cobalt catalysis [20, 21], The use of rhodium is also advantageous because of the lower isomerization. Frankel showed that with a rhodium triphenylphosphine catalyst, hydroformylation occurs only on the ninth and tenth carbon atoms of the methyl oleate [22]. 

Catalyst Description. The LPO catalyst is a triphenylphosphine modified carbonyl complex of rhodium. Triphenylphosphine, carbon monoxide, and hydrogen form labile bonds with rhodium. Exotic catalyst synthesis and complicated catalyst handling steps are avoided since the desired rhodium complex forms under reaction conditions. Early work showed that a variety of rhodium compounds might be charged initially to produce the catalyst. Final selection was made on the basis of high yield of the catalyst precursor from a commodity rhodium salt, low toxicity, and good stability to air, heat, light, and shock. 

As we have seen in Chapter 5, the mechanistic details of the hydroformylation reaction with rhodium triphenylphosphine complexes are well established. These mechanistic considerations may be modified and extrapolated to the chiral hydroformylation system. One important point to bear in mind is that bi-dentate rather than monodentate ligands are involved in the chiral hydroformylation system. 

A convenient catalyst precursor is RhH(CO)(PPh3)3. Under ambient conditions this will slowly convert 1-alkenes into the expected aldehydes, while internal alkenes hardly react. At higher temperatures pressures of 10 bar or more are required. Unless a large excess of ligand is present the catalyst will also have some isomerization activity for 1-alkenes. The internal alkenes thus formed, however, will not be hydroformylated. Accordingly, the 2-alkene concentration will increase while the 1-alkene concentration will decrease this will slow down the rate of hydroformylation. This makes the rhodium triphenylphosphine catalyst... 

Rhodium triphenylphosphine catalysts are sensitive to steric influences of the alkene substrate the rates of hydrogenation decrease with increasing alkene substi-... 

Watanabe H, Kitahara T, Motegi T et al. (1977) The stereoselective addition of phenyldimethylsilane to phenylacetylene by rhodium triphenylphosphine complexes. J.Organomet.Chem. 139 215-222... 

Since the aldehydes are easily hydrogenated to alcohols, which are the most frequently required end-products, the reactions are often run to make the alcohol. Much later it was discovered that a rhodium triphenylphosphine complex, developed by Wilkinson, was a much better catalyst for many hydroformylation reactions as it required milder conditions (lower temperature and pressure) and gave a higher selectivity. 

Homogeneous hydrogenation and 4 hydroformylation of olefins by (10) rhodium-triphenylphosphine catalysts... 

In 1987 Mitsubishi Kasei launched a 30000 tons/year plant for the production of isononanol by hydroformylation of octenes [37]. The catalyst is based on a rhodium-triphenylphosphine oxide (TPPO) complex which is stabilized after the 0x0 reaction by addition of triphenylphosphine (TPP) to avoid decomposition during the distillation of product. The rhodium-(TPP)complex formed together with excess of TPPO in the high-boiling residue is oxidized to the rhodium-TPPO... 

Figure 2. Proposed orientation of the alkyne-rhodium triphenylphosphine complex between the silicate sheets of hectorite, prior to hydrogen transfer (top) the iidtti, obtained by subtracting the thickness of the silicate sheet ( 9.6 A) from the observed 001 X-ray reflection, is a measure of the interlayer thickness. The critical dimension of 2-decyne (bottom) is defined as the minimum distance which must be spanned by the molecule when the C C axis is perpendicular to the silicate...

Two-Phase Hydroformylation of Higher Alkenes with Rhodium/Triphenylphosphine Trisulfonate (TPPTS) as Catalyst System... 

Here, we summarize briefly investigations into the two-phase hydroformylation of higher alkenes with aqueous rhodium-triphenylphosphine bisulfonate (Rh-TPPTS) catalyst systems. 

The selectivity to linear product is improved by using a cobalt trialkyl phosphine complex, but the major product is the corresponding alcohol. The use of rhodium triphenylphosphine hydrocarbonyl gives a still higher selectivity to linear aldehyde under milder conditions. These advantages are retained by using a water-soluble rhodium complex with sulphonated phosphane ligands, which provides a novel two-phase mode of operation (recently commercialized). ... 

The important discovery by Wilkinson [1] that rhodium afforded active and selective hydroformylation catalysts under mild conditions in the presence of triphenylphosphine as a hgand triggered a lot of research on hydroformylation, especially on hgand effects and mechanistic aspects. It is commonly accepted that the mechanism for the cobalt catalyzed hydroformylation as postulated by Heck and Breslow [2] can be apphed to phosphine modified rhodium carbonyl as well. Kinetic studies of the rhodium triphenylphosphine catalyst have shown that the addition of the aUcene to the hydride rhodium complex and/or the hydride migration step is probably rate-limiting [3] (Chapter 4). In most phosphine modified systems an inverse reaction rate dependency on phosphine ligand concentration or carbon monoxide pressure is observed [4]. 

---