Water-Soluble Palladium(II) Catalysts for the Alternating Co- and Terpolymerization of CO and Olefins in Aqueous Phase

Abstract

The water-soluble diphosphine (NaO3S(C6H4)CH2)2C(CH2PPh2)2 (Na2DPPPDS) was employed to prepare the bis-trifluoroacetate Pd(II) complex Pd(Na2DPPPDS)(CO2CF3)2·2THF (1). The catalytic performance of 1 in the co- and terpolymerization of CO and ethene and propene in water has been studied in different experimental conditions. In combination with both a protic acid, commonly p-toluenesulfonic acid, and an organic oxidant such as 1,4-benzoquinone, 1 forms the most efficient catalyst systems ever reported for the copolymerization of CO and ethene in water. Under comparable conditions, the activity of 1 is similar to that of the industrial Pd(II) 1,3-bis(diphenylphosphino)propane catalysts in MeOH. Unlike the latter which yield a mixture of copolymers bearing diketone, keto-ester, or diester end groups, the copolymers and terpolymers produced with the Na2DPPPDS-based catalysts have exclusively ketonic end groups for average molecular weights ranging from 10 to 30 kg mol-1 depending on the reaction conditions. In situ high-pressure NMR (HPNMR) studies have been performed in actual copolymerization conditions using D2O as solvent. The only palladium complex visible on the NMR time scale contains the diphosphine ligand and TsO- or water groups. It is suggested that this palladium complex acts as a reservoir of “(diphosphine)Pd(II)” moieties which are delivered into the catalysis cycle as Pd−H species by reaction with water and/or H+. A catalysis cycle is proposed on the basis of HPNMR experiments, the structure of the copolymers, and the occurrence of the water-gas-shift reaction.

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

“…For the water-soluble catalyst [Pd(CF 3 COO) 2 (Na 2 dppp-s)] 2THF/TsOH (TsOH/Pd = 20-300) it has been reported that after 3 h the catalytic activity, measured by plotting the consumption of the gaseous monomers versus time for 3 h reactions, is reduced to about 1/10 of the maximum value that is reached after ca. 30 s, even in the presence of benzoquinone (BQ/Pd = 80) [17]. The fact in the present case the activity remain almost constant after 3 h suggests that CH 3 COOH efficient by reoxidizes Pd(0) with formation of a Pd-H species which starts the catalytic cycle (see the proposed catalytic cycle of Scheme 1, equilibrium a).…”

“…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].…”

“…of free ligand are added (6.8 kg polyketone/g Pd * h compared to 4.8 kg polyketone/g Pd * h [17]), the addition of dppp to [Pd(AcO) 2 (dppp)] has a detrimental effect (Table 1, entries 11 and 12), as found for the system Pd(AcO) 2 /dppp/TsOH in MeOH (Table 1, entries 1 and 2) [10]. The decrease in productivity suggests that [Pd(dppp)] 2+ is (partially) converted to less active [Pd(dppp) 2 ] 2+ [28].…”

“…The activity of water-soluble Pd(II) catalysts based on the hydrophile bidentate phosphines is also significantly influenced by the nature of the anion [14][15][16][17][18][19][20]. Thus, for example employing the catalyst formed in situ from [PdX 2 L n ], dppp-s (dppp-s = 1,3-C 3 H 6 (P(C 6 H 4 -m-SO 3 Na) 2 ) 2 , the metasulphonated analogous of dppp) and an acid, under conditions close to the ones above reported, but in water as solvent and with an excess of acid (acid/ Pd = 500/1), the productivity is ca.…”

The Catalytic Copolymerization of Ethene with Carbon Monoxide Efficiently Carried out in Water-Dichloromethane-Sodium Dodecylsulfate Emulsion

“…These are mainly obtained by sulfonation of the diphosphine ligands (ca. 7 kg PK/(gPd·h) [22][23][24][25][26][27][28]), but also by fitting the phosphorus atoms with hydroxyl alkyl groups [29,30], or generally by using tenside phosphorus ligands [31].…”