Polystyrene, phosphinated

Electron spin resonance (ESR) signals, detected from phosphinated polystyrene-supported cationic rhodium catalysts both before and after use (for olefinic and ketonic substrates), have been attributed to the presence of rhodium(II) species (348). The extent of catalysis by such species generally is uncertain, although the activity of one system involving RhCls /phosphinated polystyrene has been attributed to rho-dium(II) (349). Rhodium(II) phosphine complexes have been stabilized by steric effects (350), which could pertain to the polymer alternatively (351), disproportionation of rhodium(I) could lead to rhodium(II) [Eq. (61)]. The accompanying isolated metal atoms in this case offer a potential source of ESR signals as well as the catalysis. 

New approaches to catalyst recovery and reuse have considered the use of membrane systems permeable to reactants and products but not to catalysts (370). In an attempt to overcome the problem of inaccessibility of certain catalytic sites in supported polymers, some soluble rho-dium(I), platinum(II), and palladium(II) complexes with noncross-linked phosphinated polystyrene have been used for olefin hydrogenation. The catalysts were quantitatively recovered by membrane filtration or by precipitation with hexane, but they were no more active than supported... 

The nature of the support can have a very profound influence on the catalyst activity. Thus, phosphinated polyvinyl chloride supports are fairly inactive (75), and phosphinated polystyrene catalysts are considerably more active (57), but rather less active particularly when cyclic olefins are the substrates than phosphinated silica supports (76). Silica-supported catalysts may be more active because the rhodium(I) complexes are bound to the outside of the silica surface and are, therefore, more readily available to the reactants than in the polystyrene-based catalysts where the rhodium(I) complex may be deep inside the polymer beads. If this is so, the polystyrene-based catalysts should be more valuable when it is desired to hydrogenate selectively one olefin in a mixture of olefins, whereas the silica-based catalysts should be more valuable when a rapid hydrogenation of a pure substrate is required. 

The nature of the metal complex can have a profound influence on the rate of hydrogenation, and, even in cases where similar complexes have been prepared by different routes, considerable differences in reactivities can be observed. Thus, the effectiveness of rhodium(I) complexes on phosphinated polystyrene decreases in the order, (21, 76) ... 

Andersson, C.-M. Karabelas, K. Hallberg, A. Andersson, C. Palla-dium/Phosphinated Polystyrene as a Catalyst in the Heck Arylation. A Comparative Study, J. Org. Chem. 1985, 50, 3891-3895. 

The difficulty of preparing and characterizing smaller particles has remained great. But there is now a possibility of forming clusters of a few atoms of precisely predetermined number. For example, (Rh)4 and (Rh)6 clusters have apparently been made [/. Amer. Chem. Soc. 94, 1789 (1972)] on a phosphinated polystyrene polymer. (Rh)6 catalyzed the hydrogenation of aromatics at 25°C and 1 atm H2 pressure, while (Rh)4 is apparently inactive ... 

Polymers can be modified by methods similar to those described above for metal oxides. For example, chloromethylated polystyrene reacts with diphenylphosphide to yield a phosphinated polystyrene (eqnation 4). The modified polymer can then be nsed as a hgand for a variety of... 

Metal-phosphine complexes can be inunobihzed on phos-phinated polymers through simple ligand exchange reactions. Wilkinson s Catalyst, Rh(PPh3)3Cl, has been supported on phosphinated polystyrene as shown in equation (9). The supported complex can be used as an alkene hydrogenation catalyst. 

A comparison between phosphinated polystyrene and phosphinated silica catalysts used in hydrogenation [8, 38] and hydrosilylation [72] reactions indicated, in either case, a higher reaction rate for the silica-supported analogs. This was expected and has been attributed to the better accessibility of the active sites on the silica surface. 

A useful polymer-bound catalyst has been prepared by photolysis of Cr(CO)4(norbornadiene) in the presence of polystyrene-containing pendant PPh2 groups. Photodecarbonylation of (arene)Cr(CO)3 derivatives has been employed in the preparation of (phenanthrene)(Cr(CO)2 bound to phosphinated polystyrene, in the synthesis of the structurally unusual (C6Et6)Cr(CO)2 PPh3, and in the formation of the cluster ( 7 -PhMe)CrCo2(// -C5Me5)2(CO)4. In the presence of 6,6-dimethylfulvene, photolysis of (arene)Cr(CO)3 leads to both carbon monoxide and arene elimination and the consequent formation of (6). ... 

Pentene isomerization and hydrosilylation have also been induced by irradiation of phosphinated polystyrene-bound FeCCO) complexes. ... 

Phosphinated polystyrene Phosphinated polystyrene Phosphinated polystyrene Gyanomethylated polybenzimidazole P/O ligand on polystyrene Nitroxide-functionalized polystyrene... 

When a metal complex is in equilibrium with phosphinated polystyrene, the metal binds with the polymer to form the structures [230] ... 

In qualitative kinetic studies, Hodge was also able to show that the linear soluble phosphinated polystyrene reagent was only slightly less reactive than a similar DVB cross-linked polystyrene reagent with the same alcohol substrate. Recycling of the soluble polystyrene reagent was not explicitly described. 

Hodge s group has also used linear phosphinated polystyrene to form haloolefins from carbon tetrabromide and aromatic aldehydes (27). Using 2 mol equiv of phosphine, 1 mol equiv of CBr and 1 mol equiv of -tolualdehyde at 50 C for 16 h formed a 54% yield of the dibrominated alkene. Substitution of 1% or 8% DVB cross-linked polystyrene for linear polystyrene yielded 67% and 12% of dibrominated alkene under the same conditions (Table II). 

A decline in catalytic activity with use was detected for reactions catalyzed by either species. Polymers 2 and 7 in the absence of cobalt both revealed excellent stability at 190 C (hydroformylation temperatures). This is illustrated by the TGA curves shown in Figure 4. Curve A shows an onset of decomposition for phosphinated polyphosphazene of 400 C, slightly better than that of phosphinated polystyrene (curve B, 20Z crosslinked curve C, 2Z crosslinked). Loss of phosphorus was observed over a period of 45 hours for a catalyst derived from 2 (2Z DVB crosslinked). The data depicted in Figure 5 reveal benzene, toluene, benzyl alcohol, diphenylphosphine and triphenyl phosphine as cleavage products. If one recalls the previously discussed homogeneous results it should be clear that the PPho is derived from a phosphide intermediate such as 8. ... 

Figure 4. TGA curves indicating stability of Polymer 2 and 7 at 190 C in the absence of cobalt. Curve A shows the onset of decomposition for phosphinated polyphosphazene of ilOO C, slightly better than that of phosphinated polystyrene (Curve B, 2Q% cross-linked Curve C, 2 cross-linked. ...

Phosphinated polystyrene resins have been functionalized with both bisphosphine nickel carbonyl and tristriphenylphosphinehydridocarbonylrhodium. Using this system, butadiene can be cyclodimerized to vinylcyclohexane and selectively hydroformylated at the terminal double bond in sequence. Similarly, the use of a NiBr2 chelate, reduced by NaBHj, together with the rhodium polymer permitted the linear oligomerization-selective hydroformylation of butadiene. These were both one-pot processes. 

Electron Spin Resonance (ESR). ESR has received but limited use to establish metal oxidation states/ It was shown, for example, that norbornadiene complexes of Rh(I) on a phosphinated polystyrene-DVB formed low levels of Rh(II) during the course of the hydrogenation of ketones and olefins. Supported RhCls was assigned a structure -PPh2Rh(II)Cl2 following ESR and ESCA characterization. 

Generally, the activities of polymer-bound palladium catalysts are less than those of unsupported ones, but here too there are exceptions. Kaneda et al reported that PdCl2, on phosphinated polystyrene was more active than the homogeneous situation.Rates were very solvent dependent— hydrogenation of styrene was slow in dimethyl sulfoxide optimum activity was obtained in solvents of moderate coordinating ability (see Table 6). 

A similar Ni(0) species is derived from (cyclooctadiene) nickel and a phosphinated polystyrene.The catalyst has little intrinsic activity in butadiene cyclodimerization to cyclooctadiene and vinylcyclohexene, but this was enhanced to a level of about 60-100 g-product/g-Ni/hr by the addition of AlEt2(OEt). Cyclododecatriene was not produced, indicating coordination of a phosphine to the nickel throughout the process. 

Work in this area has focused on nonphosphine supports. Polymerization of ethylene was reported with TiCU on a homopolymer or copolymer of vinylphenylphosphine AIR3 was added to activate the catalyst. With a nickel salt on a phosphinated polystyrene, addition of NaBH4 resulted in a catalyst active in the oligomerization and polymerization of acetylenic monomers (see Table 7). 

Basset investigated the catalytic properties of Mo(CO)6 attached to a phosphinated polystyrene-DVB resin.Upon treatment with ethyl-aluminum dichloride and oxygen, this slightly active system gave a conversion of cw-2-pentene of 3.4% in 20 min at room temperature. 

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