Phosphine ligands aqueous catalysis

The benzoic acid derivative 457 is formed by the carbonylation of iodoben-zene in aqueous DMF (1 1) without using a phosphine ligand at room temperature and 1 atm[311]. As optimum conditions for the technical synthesis of the anthranilic acid derivative 458, it has been found that A-acetyl protection, which has a chelating effect, is important[312]. Phase-transfer catalysis is combined with the Pd-catalyzed carbonylation of halides[3l3]. Carbonylation of 1,1-dibromoalkenes in the presence of a phase-transfer catalyst gives the gem-inal dicarboxylic acid 459. Use of a polar solvent is important[314]. Interestingly, addition of trimethylsilyl chloride (2 equiv.) increased yield of the lactone 460 remarkabiy[3l5]. Formate esters as a CO source and NaOR are used for the carbonylation of aryl iodides under a nitrogen atmosphere without using CO[316]. Chlorobenzene coordinated by Cr(CO)j is carbonylated with ethyl formate[3l7]. 

Figure 5.6 Some examples of sulfonated phosphine ligands widely used in aqueous-organic biphasic catalysis [19]...

Table I. Selected examples of sulfonated phosphine ligands for aqueous organometallic catalysis (see Figure 1 for general structure)... 

Figure 20. Non-phosphine ligands for aqueous organometallic catalysis...

There is very little information available on asymmetric hydroformylation in aqueous solutions or biphasic mixtures despite that asymmetric hydroformylation in organic solvents has long been studied very actively. This is even more surprising since enantioselective hydrogenation in aqueous media has been traditionally a focal point of aqueous organometallic catalysis and several water soluble phosphine ligands have been synthetized in enantiomerically pure form. 

Aqueous organometalHc catalysis allows the use of NH3-solutions in water for the direct synthesis of amines from olefins in a combined hydroformylation/reductive amination procedure (Scheme 4.19). The hydroformylation step was catalyzed by the proven Rh/TPPTS or Rh/BINAS (44) catalysts, while the iridium complexes formed from the same phosphine ligands and [ IrCl(COD) 2] were found suitable for the hydrogenation of the intermediate imines. With sufficiently high NH3/olefin ratios (8/1) high selectivity towards the formation of primary amines (up to 90 %) could be achieved, while in an excess of olefin the corresponding... 

Figure 4.24 a A general process schematic for aqueous biphasic catalysis, and examples ofwater-soluble phosphine ligands b the catalytic cycle for the Ruhrchemie/Rhone-Poulenc hydroformylation of propene. 

In this section catalysts containing monophosphines for aqueous-phase catalysis will be presented, the influence of ligand variation on catalyst activity being emphasized. Syntheses of hydrophilic monodentate phosphine ligands will be discussed very briefly. Reference to catalysts containing other ligands (see Sections 3.2.2 to 3.2.6) is made only where appropriate. 

Stelzer and co-workers reported a number of chiral water-soluble secondary phosphines [14], prepared by nucleophilic phosphination of primary phosphines with fluorinated aryl sulfonates in the superbasic medium DMSO/KOH. Further reaction with alkyl halides gives bidentate tertiary phosphines with P-chirality, but only racemic versions have been reported so far. Hanson et al. introduced so-called surface-active phosphines into asymmetric aqueous-phase catalysis. One of the main problems inherent to two-phase catalysis is the often very low miscibility of the substrates in the aqueous phase. Insertion of long alkyl chains between phosphorus atoms and phenyl groups in sulfonated phosphine ligands has been proven to increase reaction rates in the Rh-catalyzed hydroformylation of 1-octene [15], This concept was extended to a number of chiral ligands, i.e., the monoden-... 

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