Cationic Cyclizations and Rearrangements Promoted by a Heterogeneous Gold Catalyst

A heterogeneous gold catalyst with remarkable activity for promoting the electrophilic reactions of aryl vinyl ketones and aryl dienyl ketones is described. The catalyst is easy to prepare, is robust, and can be recycled. Low loadings are effective for different types of cationic reactions, including Nazarov cyclizations, lactonizations, and [1,2] shifts

Controlled Chain Walking for the Synthesis of Thermoplastic Polyolefin Elastomers: Synthesis, Structure, and Properties

Thermoplastic elastomers are attractive materials because of their ability to be melt-processed, reused, and recycled, unlike chemically cross-linked elastomers such as rubber. We report the synthesis and mechanical properties of polyolefin-based thermoplastic elastomer block copolymers. A simple one-pot procedure is employed, using a living arylnaphthyl-α-diimine Ni­(II) “sandwich” complex to generate high crystallinity hard blocks from 1-decene and low crystallinity soft blocks from ethylene. Various block structures are accessed, ranging from a diblock up to a heptablock copolymer. Statistical copolymers of 1-decene and ethylene are also synthesized for comparison. All resulting polymers behave as elastomers, with properties that modulate with hard and soft block composition, block architecture, and polymerization solvent. Triblock copolymers demonstrate strain at break values up to 750%, with elastic strain recoveries up to 85%. Interestingly, statistical copolymers demonstrate strain at break values upward of 1120% and elastic strain recoveries up to 77%. Creep experiments were performed to determine the resilience of these materials to deformation. It is found that higher block architectures (triblock and above) have greater resistance to strain-induced deformation than lower block architectures (diblock and statistical)

Secondary Alkene Insertion and Precision Chain-Walking: A New Route to Semicrystalline “Polyethylene” from α‑Olefins by Combining Two Rare Catalytic Events

While traditional polymerization of linear α-olefins (LAOs) typically provides amorphous, low <i>T</i>_g polymers, chain-straightening polymerization represents a route to semicrystalline materials. A series of α-diimine nickel catalysts were tested for the polymerization of various LAOs. Although known systems yielded amorphous or low-melting polymers, the “sandwich” α-diimines <b>3</b>–<b>6</b> yielded semicrystalline “polyethylene” comprised primarily of unbranched repeat units via a combination of uncommon regioselective 2,1-insertion and precision chain-walking events

Secondary Alkene Insertion and Precision Chain-Walking: A New Route to Semicrystalline “Polyethylene” from α‑Olefins by Combining Two Rare Catalytic Events

While traditional polymerization of linear α-olefins (LAOs) typically provides amorphous, low <i>T</i>_g polymers, chain-straightening polymerization represents a route to semicrystalline materials. A series of α-diimine nickel catalysts were tested for the polymerization of various LAOs. Although known systems yielded amorphous or low-melting polymers, the “sandwich” α-diimines <b>3</b>–<b>6</b> yielded semicrystalline “polyethylene” comprised primarily of unbranched repeat units via a combination of uncommon regioselective 2,1-insertion and precision chain-walking events

Secondary Alkene Insertion and Precision Chain-Walking: A New Route to Semicrystalline “Polyethylene” from α‑Olefins by Combining Two Rare Catalytic Events

While traditional polymerization of linear α-olefins (LAOs) typically provides amorphous, low <i>T</i>_g polymers, chain-straightening polymerization represents a route to semicrystalline materials. A series of α-diimine nickel catalysts were tested for the polymerization of various LAOs. Although known systems yielded amorphous or low-melting polymers, the “sandwich” α-diimines <b>3</b>–<b>6</b> yielded semicrystalline “polyethylene” comprised primarily of unbranched repeat units via a combination of uncommon regioselective 2,1-insertion and precision chain-walking events

Understanding the Insertion Pathways and Chain Walking Mechanisms of α‑Diimine Nickel Catalysts for α‑Olefin Polymerization: A ¹³C NMR Spectroscopic Investigation

Nickel α-diimine catalysts have been previously shown to perform the chain straightening polymerization of α-olefins to produce materials with melting temperatures (<i>T</i>_m) similar to linear low density polyethylene (<i>T</i>_m = 100–113 °C). Branching defects due to mechanistic errors during the polymerization currently hinder access to high density polyethylene (<i>T</i>_m = 135 °C) from α-olefins. Understanding the intricacies of nickel α-diimine catalyzed α-olefin polymerization can lead to improved ligand designs that should allow production of chain-straightened polymers. We report a ¹³C NMR study of poly­(α-olefins) produced from monomers with ¹³C-labeled carbonsspecifically 1-decene with a ¹³C-label in the 2-position and 1-dodecene with a ¹³C-label in the ω-positionusing a series of α-diimine nickel catalysts. Furthermore, we developed a mathematical model capable of quantifying the resulting ¹³C NMR data into eight unique insertion pathways: 2,1- or 1,2- insertion from the primary chain end position (1°), the penultimate chain end position (2_p^°), secondary positions on the polymer backbone (2°), and previously installed methyl groups (1_m^°). With this model, we accurately determined overall regiochemistry of insertion and overall preference for primary versus secondary insertion pathways using nickel catalysts under various conditions. Beyond this, our model provides the tools necessary for determining how ligand structure and polymerization conditions affect catalyst behavior for α-olefin polymerizations

Understanding the Insertion Pathways and Chain Walking Mechanisms of α‑Diimine Nickel Catalysts for α‑Olefin Polymerization: A ¹³C NMR Spectroscopic Investigation

Nickel α-diimine catalysts have been previously shown to perform the chain straightening polymerization of α-olefins to produce materials with melting temperatures (<i>T</i>_m) similar to linear low density polyethylene (<i>T</i>_m = 100–113 °C). Branching defects due to mechanistic errors during the polymerization currently hinder access to high density polyethylene (<i>T</i>_m = 135 °C) from α-olefins. Understanding the intricacies of nickel α-diimine catalyzed α-olefin polymerization can lead to improved ligand designs that should allow production of chain-straightened polymers. We report a ¹³C NMR study of poly­(α-olefins) produced from monomers with ¹³C-labeled carbonsspecifically 1-decene with a ¹³C-label in the 2-position and 1-dodecene with a ¹³C-label in the ω-positionusing a series of α-diimine nickel catalysts. Furthermore, we developed a mathematical model capable of quantifying the resulting ¹³C NMR data into eight unique insertion pathways: 2,1- or 1,2- insertion from the primary chain end position (1°), the penultimate chain end position (2_p^°), secondary positions on the polymer backbone (2°), and previously installed methyl groups (1_m^°). With this model, we accurately determined overall regiochemistry of insertion and overall preference for primary versus secondary insertion pathways using nickel catalysts under various conditions. Beyond this, our model provides the tools necessary for determining how ligand structure and polymerization conditions affect catalyst behavior for α-olefin polymerizations