Phosphine immobilized

Figure 25.4 shows the C CP-MAS spectra of the phosphine-immobilized polysiloxanes, (S)-CH2CH2CH2PPh2 (A) and (S)-CH2CH2PPh2 (B). Figure... 

The carbonylation of aryl halides was performed with [diiodobis(3-methyl-2(3H)-benzothiazolylidene)palladium] immobilized in tetrabutylammonium bromide (melt), [G4GiIm]BF4, [G4CiIm]Cl, [G4CiIm]Br, and tricaprylmethyl-ammonium chloride (aliquat). Palladium acetate associated with phosphines immobilized in [C4GiIm][PF6] or [G4CiIm]BF4 catalyze hydroxycarbonylation of aryl halides and benzyl chloride derivatives (Scheme 19), and the acids are separated by extraction with water. ... 

These appHcations are mosdy examples of homogeneous catalysis. Coordination catalysts that are attached to polymers via phosphine, siloxy, or other side chains have also shown promise. The catalytic specificity is often modified by such immobilization. Metal enzymes are, from this point of view, anchored coordination catalysts immobilized by the protein chains. Even multistep syntheses are possible using alternating catalysts along polymer chains. Other polynuclear coordination species, such as the homopoly and heteropoly ions, also have appHcations in reaction catalysis. 

It was recently found that the modification of neutral phosphine ligands with cationic phenylguanidinium groups represents a very powerful tool with which to immobilize Rh-complexes in ionic liquids such as [BMIM][PFg] [76]. The guani-dinium-modified triphenylphosphine ligand was prepared from the corresponding iodide salt by anion-exchange with [NH4][PFg] in aqueous solution, as shown in Scheme 5.2-15. The iodide can be prepared as previously described by Stelzer et al. [73]. 

Several approaches toward immobilization of phosphine-free ruthenium-based metathesis catalysts bearing a coordinating ether group have been made over the past 3 years [61]. This aspect has been covered in a recently published review by Blechert and Connon [8d] and will therefore not be discussed here. 

Fig. 1. shows the P MAS NMR chemical shifts for the immobilized and homogeneous catalyst. The chemical shifts at the -15.2 and -13.7 ppm correspond to PTA while the chemical shifts in the range from 20 and 40 ppm correspond to phosphine oxide. The chemical shifts at the 66 and 118 ppm seems to be those of BINAP ligand, which is confirmed by the spectrum of Ru-BINAP catalyst. This spectrum shows that PTA exist in large amount on the surface of immobilized catalyst and that BINAP ligand is intact after immobilization. 

Rhodium also has been reported as a catalyst for [2+2+2] alkyne cycloaddition in water. Uozumi et al. explored the use of an amphiphilic resin-supported rhodium-phosphine complex as catalyst (Eq. 4.60). The immobilized rhodium catalyst was effective for the [2+2+2] cycloaddition of internal alkynes in water,113 although the yields of products were not satisfactory. 

Many catalysts, both immobilized (on solid state supports) and heterogeneous, contain phosphines and other phosphorus compounds, so that solid state NMR has become an invaluable tool in the study of catalysis. 

Henderson, W., Olsen, G.M., and Bonnington, L.S. (1994) Immobilized phosphines incorporating the chiral biopolymers chitosan and chitin./. Chem. Soc. Comm., 1863-1864. 

Even under the most inert atmosphere conditions, the 31CP/MAS spectrum of the immobilized ligand showed a major signal at 6 = 42 ppm (wrt 85% H3POO characteristic of phosphine oxide rather than phosphine. This could be quantitatively reduced by HSiCl3 and this surface reaction monitored by NMR but the subsequent exchange reaction (equation [5]) generated substantial quantities of phosphine oxide and a number of different isomeric complexes were f ormed. 

Amphiphilic resin supported ruthenium(II) complexes similar to those displayed in structure 1 were employed as recyclable catalysts for dimethylformamide production from supercritical C02 itself [96]. Tertiary phosphines were attached to crosslinked polystyrene-poly(ethyleneglycol) graft copolymers (PS-PEG resin) with amino groups to form an immobilized chelating phosphine. In this case recycling was not particularly effective as catalytic activity declined with each subsequent cycle, probably due to oxidation of the phosphines and metal leaching. 

In addition to phosphine ligands, a variety of other monodentate and chelating ligands have been introduced to functionalized polymers [1-5]. For example, cyclo-pentadiene was immobilized to Merrifield resins to obtain titanocene complexes (Fig. 42.13) [102]. The immobilization of anionic cyclopentadiene ligands represents a transition between chemisorption and the presently discussed coordinative attachment of ligands. The depicted immobilization method can also be adopted for other metallocenes. The titanocene derivatives are mostly known for their high hydrogenation and isomerization activity (see also Section 42.3.6.1) [103]. 

The polymer-supported chiral phosphine obtained (Fig. 42.15) was treated with an Rh precursor and used for the enantioselective hydrogenation of dehydroamino acid derivatives. The obtained catalyst gave up to 82% ee, albeit with still low activity. Stille has developed this immobilization technique further by even more careful tuning of the polarity of the support with that of the reaction medium. For example, he introduced DIOP to a monomer vinylbenzalde-hyde in reactions analogous to those shown for the polymer in Figure 42.11. 

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