Living Polymerization of Ethylene and Copolymerization of Ethylene/Methyl Acrylate Using “Sandwich” Diimine Palladium Catalysts

Abstract

Cationic Pd(II) catalysts incorporating bulky (8-p-tolylnaphthyl) substituted diimine ligands have been synthesized and investigated for ethylene polymerization and ethylene/methyl acrylate copolymerization. Homopolymerization of ethylene at room temperature resulted in branched polyethylene with narrow M w /M n values (ca. 1.1), indicative of a living polymerization. A mechanistic study revealed that the catalyst resting state was an alkyl olefin complex and that the turnover-limiting step was migratory insertion, thus the turnover frequency is independent of ethylene concentration. Copolymerization of ethylene and methyl acrylate (MA) was also achieved. MA incorporation was found to increase linearly with MA concentration and copolymers with up to 14 mol% MA were prepared. Mechanistic studies revealed that acrylate insertion into a Pd-CH 3 bond occurs at -70 °C to yield a four-membered chelate which isomerizes first to a fivemembered chelate then to six-membered chelate. Barriers to migratory insertion of both the (diimine)PdCH 3 (C 2 H 4 ) + (17.2 kcal/mol) and (diimine)PdCH 3 ( 2 -C 2 H 3 CO 2 Me) + (15.2 kcal/mol) were measured by low temperature NMR kinetics.

(α-Diimine)palladium catalyzed ethylene polymerization and (co)polymerization with polar comonomers

“…Recently, Brookhart et al [58] reported living polymerization of ethylene at room temperature using "sandwich" -diimine palladium complexes 7a and 7b. This was also attributed to the increased axial steric bulkiness provided by the capping arene groups.…”

Influence of Ligand Backbone Structure and Connectivity on the Properties of Phosphine-Sulfonate Pd(II)/Ni(II) Catalysts

“…Subsequently, ligands L1-L3 were obtained in 39-47% yields from the reaction of 1 equivalent of n BuLi with the lithium salt in THF (tetrahydrofuran) followed by the addition of R2PCl. These ligands were characterized by by 1 H, 13 C, and 31 The reactions of ligands L1-L3 with (TMEDA)PdMe2 (TMEDA = tetramethylethylenediamine) in DMSO (dimethylsulfoxide) led to the formation of the Pd(II) complexes (Pd1-Pd3) at 41-48% yields (Scheme 2). The reaction of ligands L1-L3 with Na2CO3 and trans-[(PPh3)2Ni(Cl)Ph] afforded the desired Ni(II) complexes (Ni1-Ni3) at 34-76% yields.…”

“…The reaction of ligands L1-L3 with Na2CO3 and trans-[(PPh3)2Ni(Cl)Ph] afforded the desired Ni(II) complexes (Ni1-Ni3) at 34-76% yields. These metal complexes were characterized using 1 H, 13 C, and 31 P NMR (see Supplementary Materials, Figures S10-S20), elemental analysis and MALDI-TOF-MS (Matrix Assisted Laser Desorption Ionization-Time of Flight-Mass Spectrometry). For comparison purpose, the palladium complex Pd2′/Pd2″ and the nickel complex Ni2′/Ni1″ were prepared according to literature procedures [48,49].…”

“…Subsequently, ligands L1-L3 were obtained in 39-47% yields from the reaction of 1 equivalent of n BuLi with the lithium salt in THF (tetrahydrofuran) followed by the addition of R2PCl. These ligands were characterized by by 1 H, 13 C, and 31 P NMR (Nuclear Magnetic Resonance) spectroscopy (Bruker, Karlsruhe, Germany) (see Supplementary Materials, Figures S1-S9), elemental analysis and Mass spectrometry (EI+, Bruker Daltonics Inc., Billerica, MA, USA). The reactions of ligands L1-L3 with (TMEDA)PdMe2 (TMEDA = tetramethylethylenediamine) in DMSO (dimethylsulfoxide) led to the formation of the Pd(II) complexes (Pd1-Pd3) at 41-48% yields (Scheme 2).…”

Group 4 metal complexes bearing the aminoborane motif: origin of tandem ring-opening metathesis/vinyl-insertion polymerization

“…These tailored cyclic olefin copolymers bear the potential for functionalization through polymer-analogous reactions at the double bonds present in the copolymers. [10][11][12][13][14] In terms of polymer synthesis, the ligand system at the group 4 metals as such was designed in a way that it can switch from VIP to ROMP via abstraction of the α-proton from the growing polymer chain by the nitrogen at the pyrid-2-yl moiety. [10][11][12][13][14] In terms of polymer synthesis, the ligand system at the group 4 metals as such was designed in a way that it can switch from VIP to ROMP via abstraction of the α-proton from the growing polymer chain by the nitrogen at the pyrid-2-yl moiety.…”