Polymer-supported Pd catalyst

Palladium-catalyzed cyclic carboxylation of dienes can be utilized for the synthesis of lactones.2 Polymer-supported Pd catalyst could also be used for this reaction (Scheme 42).61 The reaction is initiated by dimerization of two molecules of diene to give a bis-7r-allylpalladium intermediate such as 123. The incorporation of C02 takes place at the internal position of an allyl unit to afford the 7r-allylpalladium carboxylate 124 which, after reductive elimination/ cyclization, yields the (5-lactone 121 (Scheme 43). 

Synthesis of polymer-supported Pd catalyst [44] For the synthesis of polymer 41, see refs. [46-48]. All solvents vs ere degassed by ultrasonication and argon purging prior to use. To a -well-stirred solution of 44 (0.36 mmol in phosphine) in THF (72 mb) was added a solution of 45 (0.12 mmol) in H2O (30 mb) and the mixture was again degassed. After the mixture had been stirred for 62 h at room temperature, a yellow precipitate formed. Water (30 mb) was added to the suspension, and THF was removed at 80 °C by distillation for 4 h in an apparatus fitted with a Dean-Stark head to leave a reddish precipitate. This precipitate was stirred at 100 °C, first in H2O (100 mb) for 12 h, then in THF (100 mb) for 3 h, and finally in further H2O (100 mb) for 12 h to wash away the unreacted palladium species and polymers. After drying in vacuo (ca. 0.1 mmHg), 41 was obtained as a dark-red solid in almost quantitative yield. 

Trying to overcome the issue of catalyst separation and Pd recovery, researcher have used immobilized Pd catalysts (polymer supported Pd catalysts... 

Polymers, such as poly(N-vinyl-2-pyrrolidone) (PVP), polyacrylamide (PAA), modified poly(2,6-dimethyl-l,4-phenylene oxide) (PPO), and polysulfone (PSF) are used to prepare polymer-supported palladium catalysts. As the data summarized in Table 5, the polymer-supported Pd catalysts are very active in the carbonylation of allylbromide. They are much more active and efficient than the homogeneous palladium catalyst, PdCl2(P(C6H5)s)2. The higher activity of the polymer-supported palladium catalyst possibly results from the increased... 

Figure 1.20 Use of a polymer supported Pd catalyst for the Heck-Mizoroki reaction reported by Patel et al. [75],...

Fig. 8.34 The general scheme and major products of proline-modified Pd-catalyzed hydrogenation of isophorone. (From C Schafer, S.C Mhadgut, N. Kugyela, M. Torok, B. Torok, Proline-induced enantioselective heterogeneous catalytic hydrogenation of isophorone on basic polymer-supported Pd catalysts, Catal. Sci. Technol. 5 (2015) 716-723. Copyright 2015 Royal Society of Chemistry).

Some conclusions can be drawn from comparison of the TOF values obtained using biphasic catalysis with literature data for the same reactions catalyzed by a polymer-supported Pd(0) catalyst (Table 2) [161]. First, although the TOFs for the dendrimer-encapsulated catalysts are consistently lower than for the polymer-supported catalysts, the values are in some cases comparable. Second, the selectivity pattern exhibited by the two types of catalysts is somewhat different. Specifically, the range of TOF numbers for biphasic catalysis is far greater than for conventional polymer catalysis, which suggests the possibility of the type of... 

Studies on the immobilization of Pt-based hydrosilylation catalysts have resulted in the development of polymer-supported Pt catalysts that exhibit high hydrosilylation and low isomerization activity, high selectivity, and stability in solventless alkene hydrosilylation at room temperature.627 Results with Rh(I) and Pt(II) complexes supported on polyamides628 and Mn-based carbonyl complexes immobilized on aminated poly(siloxane) have also been published.629 A supported Pt-Pd bimetallic colloid containing Pd as the core metal with Pt on the surface showed a remarkable shift in activity in the hydrosilylation of 1-octene.630... 

Tang, H.-G. and Sherrington, D.C., Polymer-supported Pd(ll) Wacker-type catalysts. 1. Synthesis and characterization of the catalysts. Polymer, 34, 2821, 1993. 

Influence of re-used polymer-supported Pd(PPh3)4-catalyst on the reaction time. 

Metal complexes are often used in hydrogenation reactions. These metal catalysts can be supported on a resin in the form of nanoparticles [8]. Palladium metal nanoparticles are useful as hydrogenation catalysts. They are produced by the metal exchange reaction of Pd(OAc)2 onto an appropriate acid containing resin. Once the Pd(II) is in place, the resultant polymer supported Pd(II) is reduced by NaBH4 [9]. 

Sabadie and Germain [20] have investigated the stereoselectivity of polymer-supported metal catalysts in the hydrogenation of 1,2-dimethylcyclohexene. Depending on the pressure of hydrogen, different ratios of cis- and trans-isomers (0.44 and 0.57 at 1.25 and 10 MPa, respectively) of 1,2-dimethylcyclohexanes were obtained over Pd/APSDVB catalysts. 

Polymer supported Pd(II)-glycine complex was found to be stable upto 150°C on the basis of DTA-TG analyses. A change in morphology of the catalyst is indicative of anchoring the ligand as well as the metal ions on the surface of polymer. The catalytic activity of the catalyst was tested for oxidation of toluene under various conditions. The recycling efficiency... 

More conveniently, reaction can be carried out in water without a cosolvent under certain conditions. Coupling of substrates insoluble in water such as 30 proceeds with TON up to 20000 in water when an insoluble and assembled Pd catalyst and a non-cross-linked amphiphilic (amphiphilic) polymer, containing diphenylphosphine group, are used. The catalyst system was used 10 times without any decrease in activity [44]. Also an amphiphilic resin-supported Pd catalyst can be used in water many times giving nearly quantitative yields of coupling products [45]. 

Because of its lower cost relative to Pt, there is growing interest in the development of supported Pd catalysts for formic acid oxidation. Synergies between Pd and PANl supports are well documented [94], while poly(diphenylamine-co-3-aminobenzonitrile) [95] has recently been shown to provide enhanced and more stable activities. Addition of 3-aminobenz(Miitrile to poly(diphenylamine) was found to improve the dispersion of the Pd, while both polymers eliminated the current decay seen over 1 h for carbon supported Pd. 

Simultaneously to Orellana s results, Bhanage and cowoikm desaibed a green catalytic procedure for the aminocarbonylation of aryl iodides with amines. The reaction was carried out using water as solvent and a polymer-supported Pd-NHC catalyst (PS-Pd-NHC, XXIV Scheme 5.55), which could be easily recycled up to four consecutive runs without loss of activity or selectivity. This protocol allowed the aminocarbonylation of different aryl iodides with both aryl and alkyl primary/secondary amines using 100 psi of carbon monoxide. In aU studied examples, the corresponding amides 77 were obtained in good to excellent yields, except for aromatic secondary amines [75]. 

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