Electronic Influences in Phosphinesulfonato Palladium(II) Polymerization Catalysts

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) (1a–e-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 1a–e-dmso.