Exploring Electronic and Steric Effects on the Insertion and Polymerization Reactivity of Phosphinesulfonato Pd^II Catalysts

Abstract

Thirteen different symmetric and asymmetric phosphinesulfonato palladium complexes ([{((X)1-Cl)-μ-M}n], M=Na, Li, 1=(X) (P^O)PdMe) were prepared (see Figure 1). The solid-state structures of the corresponding pyridine or lutidine complexes were determined for ((MeO)2)1-py, ((iPrO)2)1-lut, ((MeO,Me2))1-lut, ((MeO)3)1-lut, (CF3) 1-lut, and (Ph)1-lut. The reactivities of the catalysts (X) 1, obtained after chloride abstraction with AgBF4 , toward methyl acrylate (MA) were quantified through determination of the rate constants for the first and the consecutive MA insertion and the analysis of β-H and other decomposition products through NMR spectroscopy. Differences in the homo- and copolymerization of ethylene and MA regarding catalyst activity and stability over time, polymer molecular weight, and polar co-monomer incorporation were investigated. DFT calculations were performed on the main insertion steps for both monomers to rationalize the effect of the ligand substitution patterns on the polymerization behaviors of the complexes. Full analysis of the data revealed that: 1) electron-deficient catalysts polymerize with higher activity, but fast deactivation is also observed; 2) the double ortho-substituted catalysts ((MeO)2)1 and ((MeO)3)1 allow very high degrees of MA incorporation at low MA concentrations in the copolymerization; and 3) steric shielding leads to a pronounced increase in polymer molecular weight in the copolymerization. The catalyst properties induced by a given P-aryl (alkyl) moiety were combined effectively in catalysts with two different non-chelating aryl moieties, such as (cHexO/(MeO)2)1, which led to copolymers with significantly increased molecular weights compared to the prototypical (MeO)1.

Insights into Functional‐Group‐Tolerant Polymerization Catalysis with Phosphine–Sulfonamide Palladium(II) Complexes

“…Under these pseudo‐first‐order conditions, the first insertion of MA into the PdMe bond to give the first insertion product X 2 + ‐A MA is fast at 25 °C for all cationic complexes and is complete within about 30 min. The net rate constants k 1st of the first insertion are in the range (2.0–3.5)×10 −3 s −1 (Table 3, runs 1–6),20 which is close to the rate constant for PSO3 1′‐NaCl ( k 1st =3.2×10 −3 s −1 at 25 °C) 19a. The observed ratios of 2,1 to 1,2 regioselectivity in the first insertion product are about 10:1, 6:1, and 11:1 for H 1 + ‐A , DIPP 1 + ‐ A , and CF3 1 + ‐A respectively.…”

“…19 The electronic and steric effects of the phosphine–sulfonate on the insertion reactions have been studied extensively, but a clear and general picture was not obtained 9b. 18, 19a,b …”

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

“…[60][61][62] Since the seminal applications in copolymerization, it was shown that the combination of various phosphinoarylsulfonic acids with [Pd(dba) 3 ] generated active species for these transformations. It should be noted that in the case of DMF as the L 0 ligand, the resulting complex is unstable and undergoes fast oligomerization.…”

“…Acrylates were initially copolymerized with ethylene at 60-80 C in various solvents in the presence of a catalytic system generated in situ from Pd(OAc) 2 or Pd(dba) 2 and bis(2-methoxyphenyl)phosphinobenzenesulfonic acid. 45,53,58,60,61,[115][116][117] Different polyethylene elastomers with specific physical properties were prepared with this copolymerization protocol starting from ethylene and acrylates featuring epoxide, silicon, or fluorinated functional groups 118 or easily hydrolyzed into the corresponding acids. 41 Copolymerization of ethylene with methyl acrylate was selected as the model reaction to evaluate the general mechanistic features and the influence of the experimental parameters of this reaction.…”

C−H Activation and Olefin Insertion in d8 and d0 Complexes: Same Elementary Steps, Different Electronics

“…d 8 Square planar metal alkyl complexes represent another important class of homogeneous catalysts. In particular, cationic α ‐diimine Ni(II) and Pd(II) methyl complexes and related complexes have been developed as alternative polymerization catalysts to traditional d 0 metallocene or Ziegler ‐type systems, with the advantage of being tolerant towards olefins bearing polar functional groups . The functional group tolerance of these d 8 complexes has allowed for the copolymerization of unfunctionalized α ‐olefins with polar vinyl monomers such as methyl acrylate .…”