Palladium polymerization reactions

The reduction of palladium(II) with an alcoholic solution of NaBH4 [101] or by treatment in situ of the methanol-swollen material under hydrogen [129] yielded a supported palladium catalyst, referred to as self supported by the authors [101,129]. The same co-polymerization reaction was carried out inside the nanopores of a DMF-swollen gel-type resin made by DMA and MBAA (crosslinker, 4% mol) [101,129], thus obtaining a sequential IPN [131]. Also this material was transformed into a... 

Water and carbon monoxide can produce dihydrogen in situ (shift reaction), as has been shown in the synthesis of diethylketone (pentan-3-one) from ethene, CO and water in the presence of palladium(II) salts, triphenylphosphine and acids [37], Ether chain ends have been observed in some polymerization reactions [40] and low molecular weight products can also contain an ether moiety as an end group. Most likely ether chain ends are not formed by attack of alcohol at coordinated ethene in a Wacker type reaction, since this is usually followed by fast (3-hydride elimination. Instead we propose that a palladium-... 

I 3 Organic Synthesis on Polymeric Supports 3.3.2.1 Palladium-Catalyzed Reactions... 

The Tsuji-Trost-type reaction is applicable to bifunctional vinyl epoxide 144 and 1,3-diketone using a palladium catalyst as demonstrated by Koizumi, who obtained polymer 145 (Equation (67)). The reaction proceeds at 0 °C to a reflux temperature of THE. The resulting polymer 145 is isolated in a quantitative yield. The molecular weight of 145 is ca. 3000 (PDI = 2.0-2.7) when 5 mol% of Pd(PPh3)4 is employed as a catalyst. Use of Pd2(dba)3 with several bidentate phosphines such as dppe, dppp, dppb, and dppf is also effective for the polymerization reaction. Propargyl carbonate 146 also reacts with bisphenols in the presence of a palladium catalyst to afford polyethers 147 via carbon-oxygen bond formation at s - and r/) -carbon atoms (Equation (68)). 

Palladium-catalyzed a-arylation of ketones is performed with arylene dihalides and bifunctional aromatic ketones 148 to result in the bond formation at the r/) -a-carbon of the ketone, leading to polyketone 149. The reaction is carried out in the presence of Pd(0) and various phosphines. Several bidentate phosphines and bulky alkylphosphines such as dppf, BINAP, PCys, and P Bu3 are shown to be effective, while PPh3 results in no reaction. Arylene dibromide and diiodide are applicable as the co-monomers. The polymerization reaction is carried out in THE in the presence of NaO Bu at 75 °C under N2, and polymers 149 are isolated in 60-80% yields (M = 7000-15 000). Polyketone 149 is further transformed to conjugated polymer PPV by reduction of the ketone moiety with LiAlH4 followed by dehydration with an acid (Equation (69)). 

Benzofurans and dihydrobenzofurans have been prepared on polymeric supports by the palladium-mediated reaction of 2-iodophenols with dienes or alkynes (Entries 1 and 2, Table 15.9). This reaction is closely related to the synthesis of indoles from 2-iodoanilines, and probably proceeds via an intermediate palladacycle (Figure 15.3). Benzofuran and isobenzofuran derivatives have also been prepared on cross-linked polystyrene by intramolecular addition of aryl radicals to C=C double bonds and by intramolecular Heck reaction. 

Polymerization Reactions. The enantioselective co-polymerization of styrenes and carbon monoxide has been achieved by the use of a palladium catalyst based on the (5,5)-r-Bu-box ligand. Copolymerization of p-/er/-butylstyrene (TBS) and carbon monoxide in the presence of 0.1 mol % chiral catalyst afforded the alternating co-polymer with a highly isotactic microstructure and excellent optical purity (eq 22). The stereoregularity of the polymer is >98% and the polymer exhibits high molar rotation. ... 

This reaction is of particular interest since palladium is capable of selectively hydrogenating acetylene to ethylene in the presence of excess ethylene and is used to provide pure ethylene feedstocks for subsequent polymerization reactions [84]. Insights into the nature of the surface during reaction with acetylene and hydrogen described above are used as a basis for understanding the hydrogenation catalysis. 

The cationic palladium catalysts are typically prepared by reacting (cyclooctadi-enejpaUadium methyl chloride with a stoichiometric amount of the bidentate ligand to afford the (ligand) Pd(Me)Cl adduct The adduct is then reacted with an activator such as silver hexafluoroantimonate, to afford the final cationic catalyst, (hgand) l l(Me) SbF[]. The polymerization reactions were typically run at ambient temperature in toluene to afford a viscous solution of the desired copolymer. Other activators used include tris(pentafluorophenyl)borane/triethylaluminum mixtures, Nal (C,H 5(fT j)2)4 and mefhaluminoxane. 

The discovery that group IV metallocenes can be activated by methylaluminox-ane (MAO) for olefin polymerization has stimulated a renaissance in Ziegler-Natta catalysis [63]. The subsequent synthesis of well-defined metallocene catalysts has provided the opportunity to study the mechanism of the initiation, propagation, and termination steps of Ziegler-Natta polymerization reactions. Along with the advent of cationic palladium catalysts for the copolymerization of olefins and carbon monoxide [64, 65], these well-defined systems have provided extraordinary opportunities in the field of enantioselective polymerization. 

Plenio and co-workers synthesized and polymerized of l-iodo-2-methoxymethyl-3-ethynylferrocene and l-iodo-2-(A,lV-dimethylamino methyl)-3-ethynylferrocene to give 1,3-linked ferrocene-acetylene polymers.176,177 These polymers were synthesized by Sonogahira coupling reactions. These polymers showed optical activity176 or possessed functionalized side chains.177,178 Scheme 2.28 shows the reaction of diiodoferrocenes with diethynyl monomers.178,179 The palladium-catalyzed reactions led to polymers 93a,b, which when doped with iodine displayed semiconducting properties. The iodine-oxidized polymer 93a displayed an electrical conductivity of 1.3 X 10 4S/cm. 

Risse and S. Breunig, Transition metal catalyzed vinyl addition polymerizations of norbor nene derivatives with ester groups, Makromol. Chem. 193, 2915 (1992) C. Mehler and M. Risse, Addition polymerization of norbornene catalyzed by palladium(2- -) compounds. A polymerization reaction with rare chain transfer and chain termination, Macromol. 25, 4226 4228 (1992) R.G. Schulz, Polym. Lett. 4, 541 (1966). C. Tanielian, A. Kiennemann, and T. Osparpucu, Influence de differents catalyseurs abase d elements de transition du groupe VIII sur lapol3mierisation du norbor nene, Can. J. Chem. 57, 2022 (1979) A. Sen and T. W. Lai, Catalytic polymerization of acetylenes and olefins by tetrakis(acetonitrile)palladium(II) ditetrafluoroborate, Organometallics 1, 415 (1982) C. Mehler and W. Risse, Pd(II) catalyzed polymerization of norbornene derivatives, Mak romol. Chem. Rapid Commun. 12, 255 (1991). 

The catalyst cited by Shell for carrying out this polymerization reaction is palladium with a phosphine ligand. Reactor operating conditions are in the range of 85 °C (185°F) and 55-60 bars pressure (800-900 psig) [37]. 

Synthesis of conjugated p-phenylene ladder polymers by means of a microwave-assisted reaction has been achieved by Scherf et al. (Scheme 14.35) [72]. The polymerization reactions were performed in THE solution at 130 °C in the presence of palladium catalyst with phosphine ligands with irradiation in a single-mode micro-wave reactor for 11 min. Compared with conventional thermal procedures, the reaction time was reduced from days to a couple of minutes and molecular weight distributions ( PDI ca 1.8) of the polymers were changed substantially. 

MOFs can result from entrapped active catalysts, such as palladium or ruthenium nanoparticles (Scheme 3) [16,17]. Finally, the pores and channels of MOFs can act as hosts with exquisite size selectivity for photochemical and polymerization reactions. 

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