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

Abstract

Two series of cationic palladium(II) methyl complexes {[(2-MeOC 6 H 4 ) 2 PC 6 H 4 SO 2 NHC 6 H 3 (2,6-R 1 ,R 2 )]PdMe} 2 [A] 2 ( X 1 + -A: R 1 = R 2 = H: H 1 + -A; R 1 = R 2 = CH(CH 3 ) 2 : DIPP 1 + -A; R 1 = H, R 2 = CF 3 : CF3 1 + -A; A = BF 4 or SbF 6 ) and neutral palladium(II) methyl complexes {[(2-MeOC 6 H 4 ) 2 PC 6 H 4 SO 2 NC 6 H 3 (2,6-R 1 ,R 2 )]PdMe(L)} ( X 1-acetone: L= acetone; X 1-dmso: L= dimethyl sulfoxide; X 1-pyr: L= pyridine) chelated by a phosphine-sulfonamide were synthesized and fully characterized. Stoichiometric insertion of methyl acrylate (MA) into all complexes revealed that a 2,1 regiochemistry dominates in the first insertion of MA. Subsequently, for the cationic complexes X 1 + -A, b-H elimination from the 2,1-insertion product X 2 + -A MA-2,1 is overwhelmingly favored over a second MA insertion to yield two major products X 4 + -A MA-1,2 and X 5 + -A MA . By contrast, for the weakly coordinated neutral complexes X 1-acetone and X 1-dmso, a second MA insertion of the 2,1-insertion product X 2 MA-2,1 is faster than b-H elimination and gives X 3 MA as major products. For the strongly coordinated neutral complexes X 1-pyr, no second MA insertion and no b-H elimination (except for DIPP 2-pyr MA-2,1 ) were observed for the 2,1-insertion product X 2-pyr MA-2,1 . The cationic complexes X 1 + -A exhibited high catalytic activities for ethylene dimerization, affording butenes (C 4 ) with a high selectivity of up to 97.7 % (1-butene: 99.3 %). Differences in activities and selectivities suggest that the phosphine-sulfonamide ligands remain coordinated to the metal center in a bidentate fashion in the catalytically active species. By comparison, the neutral complexes X 1-acetone, X 1-dmso, and X 1-pyr showed very low activity towards ethylene to give traces of oligomers. DFT analyses taking into account the two possible coordination modes (O or N) of the sulfonamide ligand for the cationic system CF3 1 + suggested that the experimentally observed high activity in ethylene dimerization is the result of a facile first ethylene insertion into the O-coordinated PdMe isomer and a subsequent favored b-H elimination from the N-coordinated isomer formed by isomerization of the insertion product. Steric hindrance by the N-aryl substituent in the neutral systems CF3 1 and H 1 appears to contribute significantly to a higher barrier of insertion, which accounts for the experimentally observed low activity towards ethylene oligomerization.

Reversible Insertion of Carbon Dioxide at Phosphine Sulfonamido PdII–Aryl Complexes

“…40 This is in accordance with previous reports on P-oanisyl-substituted phosphine sulfonato compounds 39 as well as 1′-Me. 36 In contrast, carboxylato complexes 1-X show exo 3 configuration in the solid state with both methoxy substituents occupying the space in the z direction of the square-planar coordination sphere. This rather unusual configuration might be enabled by distortion of the square-planar geometry through the κ 2 -O,O′-coordinating carboxylato ligand.…”

“…In analogy to our previous work, , at first a catalytic cycle was computed, involving all necessary elementary reactions, as shown in Scheme . We chose a bidentate phosphine sulfonamido ligand ( L ) that had been reported by Mecking and co-workers, leaving two cis standing coordination sites for catalysis. Anisole was selected as a substrate, due to its highly nucleophilic carbon atom likely facilitating CO 2 insertion .…”

“…To synthesize carboxylato complexes 1-X the known compound 1′-Me was treated with 1 equiv of the corresponding carboxylic acid in dichloromethane at room temperature to achieve compounds 1- p An , 1-Piv , and 1-Ph in high yields as orange solids (Scheme ).…”

“…Compounds L-Na and 1′-Me were synthesized via literature procedures. 36 All other commercially available reagents and starting materials were supplied by Sigma-Aldrich, Acros Organics, or ABCR and used as received. NMR spectra were recorded with a Bruker Avance 300, Bruker Ascend 400, or Bruker Avance 600 spectrometer at the temperatures given.…”

Palladium complexes bearing an N‐heterocyclic carbene–sulfonamide ligand for cooligomerization of ethylene and polar monomers

“…Ethylene polymerization with 4a at 60 °C (Entry 1) and 80 °C (Entry 2) afforded oligoethylenes with polymerization activities of 16.2 and 98.0 kg mol −1 h −1 , respectively. The observed activities are lower than those of typical palladium catalysts such as palladium/phosphine–sulfonate (120–5330 kg mol −1 h −1 ) b, and palladium/IzQO (33–690 kg mol −1 h −1 ) catalysts, a but higher than those of palladium/phosphine–sulfonamide catalysts . Thus, we decided to perform the oligomerization at 80 °C for the following entries.…”