Control of chain transfer and chain walking by tailored metal–π interactions in polymerization catalysis

Suppression of Chain Walking and Chain Transfer in Ethylene (Co)Polymerization with Iminodibenzyl Substituents Containing Second Coordination Spheres

“…In a further comparison of the reported catalyst ( Pd-Hp ) with the nonazide dibenzosuberyl substituents, Pd2 with iminodibenzyl substituents was able to substantially suppress chain walking and promote chain transfer during ethylene polymerization, resulting in significantly less branched polyethylene with lower molecular weight (Figure ). The reason for the apparent decrease in the degree of branching may be consistent with the mechanism occurring in the corresponding nickel system (Figure ). Further 13 C NMR spectral analysis reveals that although the polyethylene obtained is relatively poorly branched, long-chain branching is still dominant in the composition of the branching types and a branch-on-branch structure exists as indicated by the existence of sec -butyl groups (Figure ).…”

“…In a further comparison of the reported catalyst (Ni-Hp) with nonazide dibenzosuberyl substituents, Ni2 with iminodibenzyl substituents was able to significantly suppress chain walking and, to some extent, chain transfer during polymerization, yielding significantly lower branched and relatively higher molecular weight polyethylene (Table 1 and Figure 3). 31 We hypothesize that the nitrogen-or electronrich phenyl group in the iminodibenzyl substituents plays the role of a second coordination sphere in suppressing chain transfer by interacting with β-H during the growing polymer chain and inhibiting it from undergoing elimination reactions (Figure 4). We performed theoretical simulations and calculations for the key intermediate Ni2-PE (Figure 4b).…”

Noncovalent Interactions in Late Transition Metal-Catalyzed Polymerization of Olefins

“…In α-diimine nickel and palladium catalysts 33 (Figure 13), weak metal−π interactions between the dibenzosuberyl substituents and the metal center are proposed to suppress β-H elimination and promote the chain transfer process during polymerization catalysis. 120 This leads to significant reductions in the molecular weight and branching density of the resultant products in ethylene (co)polymerization. Dai reported a series of flexible monoarylmethyl α-diimine nickel catalysts 34 (Figure 13).…”

Direct synthesis of poly(α-olefin) thermoplastic elastomers via controlled chain straightening using bulky α-diimine palladium complexes

“…Late-transition-metal catalysts, such as α-diimine nickel( ii ) or palladium( ii ) catalysts (Scheme 1b), exhibit a unique chain-walking process. 30–47 This process involves β-hydride elimination followed by reinsertion with opposite regiochemistry into the olefin hydride (Scheme 1c). Based on this unique process, late-transition-metal catalyzed ethylene homopolymerization has been widely used for the preparation of TPEs.…”