Rh catalyzed hydroformylation

Obviously, the use of a nonvolatile ionic liquid simplifies the distillative workup of volatile products, especially in comparison with the use of low-boiling solvents, where it may save the distillation of the solvent during product isolation. Moreover, common problems related to the formation of azeotropic mixtures of the volatile solvents and the product/by-products formed are avoided by use of a nonvolatile ionic liquid. In the Rh-catalyzed hydroformylation of 3-pentenoic acid methyl ester it was even found that the addition of ionic liquid was able to stabilize the homogeneous catalyst during the thermal stress of product distillation (Figure 5.2-1) [21]. This option may be especially attractive technically, due to the fact that the stabilizing effects could already be observed even with quite small amounts of added ionic liquid. 

Table 5.2-1 Comparison of different phosphine ligands in the Rh-catalyzed hydroformylation of 1-octene in [BMIM][PFd.

Cationic phosphine ligands containing guanidiniumphenyl moieties were originally developed in order to make use of their pronounced solubility in water [72, 73]. They were shown to form active catalytic systems in Pd-mediated C-C coupling reactions between aryl iodides and alkynes (Castro-Stephens-Sonogashira reaction) [72, 74] and Rh-catalyzed hydroformylation of olefins in aqueous two-phase systems [75]. 

Olivier-Bourbigou s group, for example, has recently shown that phosphite ligands can be used in Rh-catalyzed hydroformylation in ionic liquids as well as the well loiown phosphine systems [81]. Since phosphite ligands are usually unstable in aqueous media, this adds (apart from the much better solubility of higher olefins in... 

Another interesting recent development is the continuous, Rh-catalyzed hydroformylation of 1-octene in the unconventional biphasic system [BMIM][PF6]/scC02, described by Cole-Hamilton et al. [84]. This specific example is described in more detail, together with other recent work in ionic liquid/scC02 systems, in Section 5.4. 

In the author s group, much lower-melting benzenesulfonate, tosylate, or octyl-sulfate ionic liquids have recently been obtained in combination with imidazolium ions. These systems have been successfully applied as catalyst media for the biphasic, Rh-catalyzed hydroformylation of 1-octene [14]. The catalyst activities obtained with these systems were in all cases equal to or even higher than those found with the commonly used [BMIM][PF6]. Taking into account the much lower costs of the ionic medium, the better hydrolysis stability, and the wider disposal options relating to, for example, an octylsulfate ionic liquid in comparison to [BMIM][PF6], there is no real reason to center future hydroformylation research around hexafluorophosphate ionic liquids. 

Figure 5.3-4 Turnover frequency of Rh-catalyzed hydroformylation as a function of 1-hexene...

For long chain olefins, the hydroformylation generally proceeds slowly and with low selectivity in two-phase systems due to their poor solubility in water. Monflier et al. recently reported a conversion of up to 100% and a regioselectivity of up to 95% for the Rh-catalyzed hydroformylation of dec-l-ene in water, free of organic solvent, in the presence of partially methylated 6-cyclodextrins (Eq. 3.42).173... 

Table 3 4x4 ligand matrix of aminopyridine (4a-d)/isoquinolone (5a-d) derived self-assembled bidentate ligands in the [Rh]-catalyzed hydroformylation of l-octenea... 

Phosphites have been used as ligands in Rh-catalyzed hydroformylation from the early days since their introduction in 1969.205 206 Identification of complexes occurred more recently. Ziolkowski and Trzeciak have studied extensively the use of phosphite ligands in the Rh-catalyzed hydroformylation of alkenes.207-210 The ligand tris(2-/er/-butyl-4-methylphenyl) phosphite (65) leads to extremely fast catalysis and in situ spectroscopy showed that under the reaction conditions only a mono-ligated complex [Rh(H)(CO)3(65)], (66), is formed due the bulkiness of the ligand.211-213... 

Chiral thioether-phosphite ligands (125) derived from 1,2-O-isopropylidenexylofuranose have been synthesized. Reaction of these chiral ligands with [Rh(cod)2]BF4 yielded [Rh(cod)(125)]BF4. These ligands were tested in the Rh-catalyzed hydroformylation of styrene. The hydroformylation results (ee values were insignificant) are discussed according to the solution structure of the species formed under hydroformylation conditions. HP NMR studies show that only the phosphite is coordinated during the catalytic reaction.390... 

Relatively little work has been devoted to the characterization of complexes in water and generally it has been assumed that for Rh-catalyzed hydroformylation similar species are formed in water as inorganic solvents, i.e., [RhH(L)2(CO)2] and [RhH(L)3(CO)] are the major species. Therefore, few references can be mentioned here which contain information about coordination complexes. In addition, a few, more recent, studies will be mentioned which do not report in situ coordination compounds. A HP NMR study of [RhH(TPPTS)3(CO)] has been reported. It was... 

In the presence of tetramethyltin, 1-bromonauclefine reacts with CO in a Pd-catalyzed carbonylation to give the alkaloid naucletine [202], Dong and Busacca effected a new synthesis of tryptamines and tryptophols via a Rh-catalyzed hydroformylation of functionalized anilines that are prepared by a standard Heck reaction, as shown for the preparation of tryptamine sulfonamide 325 [423]. This reaction is applicable to ring-substituted tryptamines (Cl, Br, F. OMe, CF3). Likewise, the Rh-catalyzed carbonylation of o-alkynylanilines, which were prepared by a Pd-catalyzed Sonogashira coupling, leads to oxindoles (60-86% yields) [424],... 

The intermolecular Heck reaction of 3-bromofuran and tosylallyamine 88 gave adduct 89 under the classical Heck conditions [79], Subsequent Rh-catalyzed hydroformylation with ring closure occurred regioselectively to furnish the hydroxypyrrolidine, which was dehydrated using catalytic HC1 to afford dihydropyrrole 90. 

Inspired by the excellent results using the BINAPHOS ligands, new phosphine-phosphite ligands with different backbones have been developed in recent years. Unfortunately, their Rh-catalyzed hydroformylation provided low-to-moderate enantioselectivity (ee s from 20 to 62%) [35,36,65]. 

Schemes Rh-catalyzed hydroformylation of -octene using phosphites 14,17, and 19...

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