Copolymerization of Carbon Monoxide with Ethene Catalyzed by Palladium(II) Complexes of 1,3-Bis(diphenylphosphino)propane Ligands Bearing Different Substituents on the Carbon Backbone

Abstract

In this work are described the syntheses of several new dppp-like ligands (dppp =1,3-bis(diphenylphosphino)propane) bearing different substituents on the carbon backbone and of their palladium(II) complexes with acetate or trifluoroacetate coligands (L). The complexes exhibit the general formula Pd(P−P)(L)2 and have been employed as catalyst precursors for the copolymerization of ethene and carbon monoxide in MeOH under experimental conditions that are comparable to those reported in the relevant literature and patents for dppp-based Pd(II) copolymerization catalysts. It has been found that the introduction of alkyl substituents in the 2-position of the carbon backbone of dppp does not significantly improve the performance of the corresponding catalyst precursors (highest productivity value 6.2 kg of copolymer (g of Pd h)-1 vs 5.4 kg of copolymer (g of Pd h)-1 for Pd(dppp)(L)2). In contrast, the productivity increases remarkably when methyl groups are introduced in both 1-positions of the diphosphine ligand, particularly with R,S (S,R) stereochemistry as in meso-CH2(CH3CHPPh2)2 (productivity of 8.0 kg of copolymer (g of Pd h)-1). On the basis of NMR and cyclic voltammetric studies of the catalyst precursors, it is suggested that the increased productivity provided by the C1-substituted ligands is both electronic and steric in nature. In situ high-pressure NMR experiments in sapphire tubes equipped with Ti alloy valves showed that the only phosphorus-containing species visible on the NMR time scale in effective copolymerization conditions are Pd(II) complexes with the formula Pd(diphosphine)X2 (X = p-toluenesulfonate, trifluoroacetate, or MeOH). It has been proposed that these Pd(II) complexes act as a reservoir of [Pd(diphosphine)]2+ moieties which may either be delivered into the catalysis cycle by action of various reagents (MeOH, H+, H2O, H2) or be withdrawn after the termination step and watched over deactivation paths.

Metal‐Catalyzed Synthesis of Alternating Copolymers

“…For instance, Bianchini et al demonstrated that the introduction of alkyl groups in the 2-position of the carbon backbone of dppp does not improve the catalytic activity of the corresponding palladium (II) precursors. [28] By contrast, a considerable increase of the productivity (i.e., more than 50%) was obtained when alkyl groups were introduced in both 1-and 3-position of the dppp backbone, to yield both the meso-2,4-bis(diphenylphosphino)pentane (meso-bdpp, 2, Figure 1) and the rac-bdpp. Under comparable experimental conditions, meso-bdpp has been reported to be more active in the palladiumcatalyzed CO/ethylene copolymerization than dppp or racbdpp.…”

Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study

“…BH 3 (27) gave the boron-protected bidentate phosphine ligands [23][24][25][26]. [61,62] Deboronation of the phosphines 23-26 was achieved by the addition of an excess of tetrafluoroboric acid to give an in situ prepared phosphonium salt that was then reduced to the desired phosphine by the addition of potassium hydroxide.…”

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

“…In the present work the precursor is [PdCl 2 (dppf)], but since it is well known that water is capable of coordinating Pd(II) with the formation of aqua-complexes and also that the monomers are capable to coordinate Pd(II) [41,42], it is plausible to suppose that [PdCl 2 (dppf)] undergoes equilibrium 1 (Scheme 1) [28,43]. Upon increasing the concentration of H 2 O, the formation of a cationic aqua-complex is favored also by the increasing of the dielectric constant of the reaction medium, which favors the separation of the charges.…”