A series of palladium/alkylphosphine-sulfonate catalysts were synthesized and examined in the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. Catalysts with alkylphosphine-sulfonate ligands containing sterically demanding alkyl substituents afforded (co)polymers whose molecular weight was increased by up to 2 orders of magnitude relative to polymers obtained from previously reported catalyst systems. The polymer molecular weight was found to be closely correlated to the Sterimol B5 parameter of the alkyl substituents in the alkylphosphine-sulfonate ligands. Thus, the use of bulky alkylphosphine-sulfonate ligands represents an effective and versatile method to prepare high-molecular-weight copolymers of ethylene and various polar monomers, which are difficult to obtain by previously reported methods.

The mechanism of linear polyethylene formation catalyzed by palladium/phosphine−sulfonate and the effect of the ligand structure on the catalytic performance, such as linearity and molecular weight of the polyethylene, were reinvestigated theoretically and experimentally. We used dispersion-corrected density functional theory (DFT-D3) to study the entire mechanism of polyethylene formation from (R 2 PC 6 H 4 SO 3 )PdMe(2,6-lutidine) (R = Me, t-Bu) and elucidated the key steps that determine the molecular weight and linearity of the polyethylene. The alkylpalladium ethylene complex is the key intermediate for both linear propagation and β-hydride elimination from the growing polymer chain. On the basis of the key species, the effects of substituents on the phosphorus atom (R = t-Bu, i-Pr, Cy, Men, Ph, 2-MeOC 6 H 4 , biAr) were further investigated theoretically to explain the experimental results in a comprehensive manner. Thus, the experimental trend of molecular weights of polyethylene could be correlated to the ΔΔG ⧧ value between (i) the transition state of linear propagation and (ii) the transition state of the path for ethylene dissociation leading to β-hydride elimination. Moreover, the experimental behavior of the catalysts under varied ethylene pressure was well explained by our computation on the small set of key species elucidated from the entire mechanism. In our additional experimental investigations, [o-Ani 2 PC 6 H 4 SO 3 ]PdH[P(t-Bu) 3 ] catalyzed a hydrogen/ deuterium exchange reaction between ethylene and MeOD. The deuterium incorporation from MeOD into the main chain of polyethylene, therefore, can be explained by the incorporation of deuterated ethylene formed by a small amount of Pd−H species. These insights into the palladium/phosphine−sulfonate system provide a comprehensive understanding of how the phosphine−sulfonate ligands function to produce linear polyethylene.

Coordination-insertion copolymerization of allyl monomers with ethylene was developed by using a palladium/phosphine-sulfonate catalyst. A variety of allyl monomers, including allyl acetate, allyl alcohol, protected allylamines, and allyl halides, were copolymerized with ethylene to form highly linear copolymers that possess in-chain -CH(2)CH(CH(2)FG)- units.

Ti (la), M = Zr (lb), M = Hf (lc)), , and Me2C(3-i-Bu-C6H3)-(3-Me-C9H5)ZrCl2 (3) were synthesized and separated into threo and erythro isomers by repeated recrystallization. The molecular structure of MeaCiS-i-BuCaHsXS-i-Bu-CgHelZrCla (threo-lb) was determined by X-ray crystallography. Polymerization of propylene with one of these metallocene complexes (iAreo-lb) coupled with MAO (methylaluminoxane) in toluene was found to afford a highly isotactic polymer of Mw 105 000 with % mm > 99.6 which shows an extremely high melting point of 161 °C.

A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, that is, [κ 2 -(Pd/ BPMO), were synthesized and evaluated as catalysts for the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. X-ray crystallographic analyses revealed that these Pd/BPMO complexes exhibit significantly narrower bite angles and longer Pd−O bonds than Pd/BPMO complexes bearing a phenylene linker, while maintaining almost constant Pd−P bond lengths. Among the complexes synthesized, menthyl-substituted complex 3f (R 1 = (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-yl; R 2 = Me) showed the best catalytic performance in the homo-and copolymerization in terms of molecular weight and polymerization activity. Meanwhile, complex 3e (R 1 = t-Bu; R 2 = Me) exhibited a markedly higher incorporation of comonomers in the copolymerization of ethylene and allyl acetate (≤12.0 mol %) or methyl methacrylate (≤0.6 mol %). The catalytic system represents one of the first examples of late-transition-metal complexes bearing an alkylene-bridged bidentate ligand that afford high-molecular-weight copolymers from the copolymerization of ethylene and polar monomers.