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Electronic Influences in Phosphinesulfonato Palladium(II) Polymerization Catalysts

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posted on 26.08.2013, 00:00 by Philipp Wucher, Verena Goldbach, Stefan Mecking
To study the influence of electronics on catalytic polymerization properties independent from sterics, phosphinesulfonato Pd­(II) complexes bearing remotely located substituents on the nonchelating P-bound aryls [κ2-(P,O)-(4-R-2-anisyl)2PC6H4SO2O]­Pd­(Me)­(dmso) (1ae-dmso: 1a, R = CF3; 1b, R = Cl; 1c, R = H; 1d, R = CH3; 1e, R = OCH3) were prepared. The electron-poor complex 1a-dmso (4-CF3) undergoes the fastest insertion of methyl acrylate (MA) and is the most active for ethylene polymerization. The polyethylene molecular weight increases by a factor of 2 for the more electron rich complex 1e-dmso (4-OCH3) (Mn = 17 × 103 vs 8 × 103 for 1a-dmso (4-CF3)). MA/ethylene copolymerization experiments revealed that the MA incorporation ratio and copolymer molecular weights are largely independent of the electronic nature of the remote substituents. These trends were further confirmed by studies of two mixed P-aryl/-alkyl complexes 1f-dmso ([κ2-(2,4,6-(OMe)3C6H2)­(tBu)PC6H4SO2O]­Pd­(Me)­(dmso)) and 1g-dmso ([κ2-(C6H5)­(tBu)PC6H4SO2O]­Pd­(Me)­(dmso)). In ethylene/MA copolymerization, 1f-dmso affords a significantly higher molecular weight polymer with reasonable MA incorporation (Mn = 12 × 103 and 7.7 mol % MA) and activities similar to those observed for complexes 1ae-dmso.