Ligand effects in the non-alternating CO–ethylene copolymerization by palladium(ii) catalysis

Abstract

In this paper we report on a comparative study of the non-alternating CO-C(2)H(4) copolymerization catalyzed by neutral Pd(II) complexes with the phosphine-sulfonate ligands bis(o-methoxyphenyl)phosphinophenylenesulfonate and bis(o-methoxyphenyl)phosphino-ethylenesulfonate. The former ligand, featuring a lower skeletal flexibility, has been found to form more active catalysts as well as produce polyketones with higher molecular weight and higher extra-ethylene incorporation. Operando high-pressure NMR studies have allowed us to intercept, for the first time, Pd(II)(phosphine-sulfonate) beta-chelates in the non-alternating copolymerization cycle, while model organometallic reactions have contributed to demonstrate that Pd(II) (phosphine-sulfonate) fragments do not form stable carbonyl complexes. The opening of the beta-chelates has been found to be a viable process by either comonomer, which contrasts with the behaviour of Pd(II) (chelating diphosphine) catalysts for the perfectly alternating copolymerization.

Photodegradable branched polyethylenes from carbon monoxide copolymerization under benign conditions

“…A comparison with the relative monomer reactivities in catalytic copolymerization is instructive. Data for ethylene-CO copolymerizations by neutral Pd(II) phosphinosulfonato catalysts, which are capable of generating non-alternating motifs at high ethylene/CO ratios in the reaction mixture have been reported by different authors [23][24][25] . Compared with polyketones from free-radical copolymerization, catalytically synthesized polymers contain more alternating segments even at comparable CO incorporations around 10%.…”

Synthesis and Applications in Catalysis of Metal Complexes with Chelating Phosphinosulfonate Ligands

“…32 Variation of aryl groups has allowed the preparation of a high diversity of imidazolinium sulfonate zwitterions, precursors of NHC-sulfonate ligands ( Fig. 37 38,39 It should be noted that decomposition of alkyl or hydride palladium(II) complexes containing a ligand such as 1d or 3a also led to the formation of similar cis bis(chelates). 33 Scheme 3.14 Preparation of the enantiomerically enriched imidazoliniumbenzenesulfonate 9e.…”

“…3.4). 37 Ammonium sulfonates generated from the reaction of phosphinosulfonic acids 2a-H and 3a-H with tertiary aliphatic amines reacted with [PdMeCl(COD)] to afford anionic square planar palladium(II) [PdCl(P^O)Me] À complexes where the methyl ligand is located at the cis-position with respect to the phosphorus atom. leading to neutral transition metal complexes with unique properties.…”

“…33 Scheme 3.14 Preparation of the enantiomerically enriched imidazoliniumbenzenesulfonate 9e. 37,41 Under atmospheric pressure of CO, insertion occurred on the anionic palladium to give the corresponding acetyl anionic palladium [PdCl(3a)Ac] À complex. 37 38,39 It should be noted that decomposition of alkyl or hydride palladium(II) complexes containing a ligand such as 1d or 3a also led to the formation of similar cis bis(chelates).…”

“…9 The nonalternating character of the copolymerization of ethylene and CO was shown in reactions carried out at 100-120 C with various C 2 H 4 /CO relative pressures in the presence of O-alkoxydiphenylphosphinobenzene sulfonic acid as phosphinosulfonate ligand precursors (Scheme 3.56). 37,130,131 Nonalternating linear ethylene/CO copolymers have then been prepared with the objective of modifying physical properties as a function of relative contents of each monomer. 39 The multiple insertion of ethylene was understood as the result of the easier insertion of ethylene into the neutral five-membered palladacycle due to its lower stability as compared to cationic palladium diphosphine.…”