Highly Syndiotactic Polymerizationof ortho-Methoxystyrene with β-Diketiminato Rare-earth Metal Complexes
The coordination polymerization of polar monomers encounters the significantly challenging and long standing problem in the academic research field,similar to other olefins bearing polar functional groups.However,the key to polymerization is the design of the catalyst.β-Diketiminate ligands have gained increasing popularity since the mid 1990s due to their suitability as spectator ligands.Additionally,β-diketiminate ligands have become some of the most widely used bidentate N-donor ligands in coordination chemistry nowadays.Interest in β-diketiminate complexes was focused mostly on their application in olefin,notably ethylene,polymerization or on investigations of the ligand coordination mode,which varies between in-plane κ2-coordination and out-of-plane η4/5-coordination.In this work,a series of rare earth metal complexes 1-3 bearing β-diketiminiato ligands featuring aliphatic substituents were designed and synthesized readily.In the presence of cocatalysts[Ph3C][B(C6F5)4]and AliBu3,complexes 2 and 3 were highly active for polymerization of ortho-methoxystyrene(oMOS)to afford syndiotactic polymers(rrrr＞99％).These methoxyl functionalized polystyrenes have melting temperatures around 240 ℃ and a Tg of-90 ℃.Complex 2 showed high 1,4 selectivity(88.6％)for isoprene polymerization.Finally,we demenstrate that the stereoselectivity was determined by the coordination patterns of monomer using density functional theory(DFT)calculations clearly.
Rare-earth metal catalystsSyndiotacticOrtho-methoxystyrene
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