Chain-Transfer Mechanisms of the Alternating Copolymerization of Carbon Monoxide and Ethene Catalyzed by Palladium(II) Complexes:  Rearrangement to Highly Reactive Enolates

Zuideveld, Martin A.; Kamer, Paul C. J.; Leeuwen, Piet W. N. M. van; Klusener, Peter A. A.; Stil, and Hans A.; Roobeek, C. F.

doi:10.1021/ja980914+

Cited by 105 publications

(86 citation statements)

References 32 publications

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“…Actually, it is known that protonolysis involves a preequilibrium of a ␤-chelate species with its enolate isomer by a ␤-H elimination/hydride migration and protonation to the more nucleophilic oxygen atom to give an enol, which rearranges to the ketone [55]. Termination by protonation of this enolate finally produces the ketone-terminating end-group and a Pd-OH + or a Pd-OC(O)H + species, which are converted to active Pd-H + via a partial water gas-shift reaction (step 7a) or a ␤-H elimination from Pd-OC(O)H + (step 7b).…”

Section: Proposed Catalytic Cyclementioning

confidence: 99%

Terpolymerization of propene and ethene with carbon monoxide catalyzed by [PdCl2(dppf)] in HCOOH–H2O as a solvent [dppf=1,1′-bis(diphenylphosphino)ferrocene]

Vavasori¹,

Ronchin²,

Toniolo³

2010

Applied Catalysis A: General

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a b s t r a c tThe [PdCl 2 (dppf)] complex efficiently catalyzes the terpolymerization of propene and ethene with carbon monoxide in HCOOH-H 2 O as a solvent, when H 2 O concentration ranges between 50 and 65 molar %. The productivity, the melting temperature and the viscosity average molecular weight of the terpolymer depend on the propene concentration and on the reaction time.The NMR analysis of the polymer composition indicates the presence along the chain mainly of ethene-CO units together with a low percent of propene-CO units.A reaction mechanism is proposed and discussed.

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Section: Proposed Catalytic Cyclementioning

confidence: 99%

Terpolymerization of propene and ethene with carbon monoxide catalyzed by [PdCl2(dppf)] in HCOOH–H2O as a solvent [dppf=1,1′-bis(diphenylphosphino)ferrocene]

Vavasori¹,

Ronchin²,

Toniolo³

2010

Applied Catalysis A: General

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“…The mechanism proposed to explain deuterium enrichment in the 2-position with respect to 1-position involves a pre-equilibrium of the b-chelate with its enolate isomer by a b-H elimination/ hydride migration and protonation to the more nucleophilic oxygen atom to give an enol, which rearranges to the ketone [16,47]. When protonolysis occurs by H 2 O, the binuclear complex ½Pdðl-OHÞðP-PÞ 2 2þ , which may form if excess acid is not used, reacts with CO with regeneration of a Pd-H + species after CO 2 evolution [48].…”

Section: Co-c 2 H 4 Copolymerizationmentioning

confidence: 99%

Synthesis, characterization and X-ray structure of [Pd(SO4)(dppp)]·H2O, a catalyst for the CO-ethene copolymerization [dppp=1,3-bis(diphenylphosphino)propane]

Cavinato

Vavasori

Toniolo

et al. 2005

Inorganica Chimica Acta

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The title complex has been synthesized by first reacting dppp with Pd(AcO) 2 in acetone and then with NaHSO 4 in water. It has been characterized by IR, NMR and X-ray diffraction studies. The 31 P NMR spectrum in DMSO shows a singlet at 16.62 ppm indicating that the two P atoms are equivalent and that the sulfate anion is weakly coordinating. The X-ray structure shows that the Pd atom is surrounded in an almost regular square planar environment by the two P atoms and by two O atoms of the sulfate anion and that the neutral complex is accompanied by a water molecule of crystallization. The Pd-P distances (2.217(1) and 2.233(1)) and the P-Pd-P angle (90.78(3)°) are close to those found in other complexes where the chelating diphosphine is the same. Also the Pd-O distances and the O-Pd-O bond angle are comparable to those of other relevant chelating ligands.In MeOH, the title complex, in combination with H 2 SO 4 , catalyses the CO-ethene copolymerization. The productivity reaches a maximum upon increasing the H 2 SO 4 /Pd ratio up to ca. 470 (7650 g of polyketone/g Pd h at 90°C and 45 atm, CO/ethene 1/1). The viscosity of the polyketone passes through a maximum of 0.95 dL/g in m-cresol when the above ratio is ca. 100. It has been proposed that acid promotes the copolymerization process by destabilizing the b-and c-chelates intermediates involved in chain growing process, thus favoring the insertion of the monomers. At relatively high acid concentration the lowering of productivity and viscosity suggests that the sulfate anion competes with the monomers for the coordination to the metal center.In H 2 O-CH 3 COOH as a solvent the productivity strongly depends on the H 2 O/CH 3 COOH ratio, as it passes through a maximum of 12 000 g polymer/g Pd h in the presence of ca. 60% of H 2 O. The productivity is significantly lower than that found when the acetate and chloride analogues are used (27 000 g polyketone/g Pd AE h). Thus, it is likely that the sulfate anion assists significantly the copolymerization process even though the concentration of CH 3 COOH/CH 3 COO À is much preponderant.

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“…Excess of acid inhibits the hydrolysis of a Pd-acyl bond as observed in water with sulphonated dppp ligands [15,20]. The overall mechanism is basically similar to the one proposed by Bianchini et al with water-soluble Pd(II) catalysts [17] (species (3) can be actually a ␤-chelate at equilibrium with an enolate isomer which undergoes protonation of the C2 carbon atom [29]). The CH 3 COOH-H 2 O reaction medium not only guarantees a sufficient solubility of the two monomers and the catalytic system but, more important, on one hand the acid stabilizes the [Pd-H] + species (equilibrium a of Scheme 1; see also the last equilibrium of reactions 1), on the other it is likely that water prevents coordination of AcO to the cationic hydride (1) [28].…”

Section: On the Proposed Catalytic Cyclementioning

confidence: 60%

Highly active [Pd(AcO)2(dppp)] catalyst for the CO-C2H4 copolymerization in H2O-CH3COOH solvent [dppp = 1,3-bis(diphenylphosphino)propane]

Vavasori¹,

Toniolo²,

Cavinato

et al. 2003

Journal of Molecular Catalysis A: Chemical

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In MeOH, [Pd(AcO) 2 (dppp)] becomes an efficient catalyst for the perfectly alternated CO-C 2 H 4 copolymerization when used in combination of a relatively large amount of CH 3 COOH (CH 3 COOH/Pd, ca. 2.0 × 10 4 ). Under 4.56 MPa (CO/C 2 H 4 = 1/1), at 90 • C, 7.5 kg polyketone/g Pd * h are obtained. A significantly higher productivity is obtained in H 2 O-CH 3 COOH, in place of MeOH (27.5 kg polymer/g Pd * h under 4.56 MPa (CO/C 2 H 4 = 1/1), 90 • C, H 2 O = 37% (mol/mol)). Under these conditions the catalyst undergoes only a minor deactivation with time as after 3 h the productivity decreases only by ca. 10%.The 13 C NMR analysis shows that [Pd(AcO) 2 (dppp)] in CH 3 COOH-H 2 O yields a perfectly alternated polyketone of ca. 8000 g/mol bearing only ketonic end groups. During the course of the copolymerization reaction CO 2 forms in significant amount. These findings suggest that the insertion of C 2 H 4 into Pd-H bond starts the catalytic cycle, and that alternating insertions of the monomers followed by protonolysis of a Pd-C bond of a Pd-CH 2 -CH 2 -(CO-C 2 H 4 ) n -H growing chain yields the polymer with only keto ending groups and a Pd-OH species; a reaction closely related to the WGS reproduces the starting Pd-hydride; deprotonation of this species to inactive Pd(0) is prevented by the acid.

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Chain-Transfer Mechanisms of the Alternating Copolymerization of Carbon Monoxide and Ethene Catalyzed by Palladium(II) Complexes: Rearrangement to Highly Reactive Enolates

Cited by 105 publications

References 32 publications

Terpolymerization of propene and ethene with carbon monoxide catalyzed by [PdCl2(dppf)] in HCOOH–H2O as a solvent [dppf=1,1′-bis(diphenylphosphino)ferrocene]

Terpolymerization of propene and ethene with carbon monoxide catalyzed by [PdCl2(dppf)] in HCOOH–H2O as a solvent [dppf=1,1′-bis(diphenylphosphino)ferrocene]

Synthesis, characterization and X-ray structure of [Pd(SO4)(dppp)]·H2O, a catalyst for the CO-ethene copolymerization [dppp=1,3-bis(diphenylphosphino)propane]

Highly active [Pd(AcO)2(dppp)] catalyst for the CO-C2H4 copolymerization in H2O-CH3COOH solvent [dppp = 1,3-bis(diphenylphosphino)propane]

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