In contrast to traditional diimine-palladium complexes, sterically hindered "sandwich" diimine-palladium adducts act as olefin-isomerization catalysts. Terminal olefins are selectively converted to 2-olefins by a sequence of migratory insertion,,6-hydride elimination, and olefin displacement. The reaction is performed at 0 degrees C with 1 mol % of an air-stable precatalyst and tolerates functional groups such as ketones, silyl ethers, and halogens. The isomerization may be used to produce silyl enol ethers from protected allylic alcohols.
Secondary Alkene Insertion and Precision Chain-Walking: A New Route to Semicrystalline “Polyethylene” from α-Olefins by Combining Two Rare Catalytic Events
摘要:
While traditional polymerization of linear alpha-olefins (LAOs) typically provides amorphous, low T-g polymers, chain-straightening polymerization represents a route to semicrystalline materials. A series of alpha-diimine nickel catalysts were tested for the polymerization of various LAOs. Although known systems yielded amorphous or low-melting polymers, the "sandwich" alpha-diimines 3-6 yielded semicrystalline "polyethylene" comprised primarily of unbranched repeat units via a combination of uncommon regioselective 2,1-insertion and precision chain-walking events.