Synthesis and Reactivity of Palladium(II) Alkyl Complexes that Contain Phosphine-cyclopentanesulfonate Ligands

The synthesis of the phosphine-cyclopentanesulfonate pro-ligands Li/K[2-PPh(2)cyclopentanesulfonate] (Li/K[2a]), Li/K[2P(2-OMe-Ph)(2)-cydopentanesulfonate] (Li/K[21,]), and H[2b], and the corresponding Pd(II) alkyl complexes (K-2-P,O-2a)PdMe(pyridine) (3a) and (K-2-P,O-2b)PdMe(pyridine) (3b) is described. The sulfonate-bridged base-free dimer {(2b)PdMe}(2) (4b) was synthesized by abstraction of pyridine from 3b using B(C6F5)(3). The borane-coordinated base-free dimer [{2b center dot B(C6F5)(3)}PdMe](2) (5b), in which B(C6F5)(3) binds to a sulfonate oxygen, was prepared by addition of 1 equiv of B(C6F5)(3) per Pd to 4b or addition of 2 equiv of B(C6F5)(3) to 3b. Compounds 3b, 4b, and 5b polymerize ethylene with low activity (up to 210 kg mol(-1) h(-1) at 250 psi and 80 degrees C) to linear polyethylene (M-n = 1950-5250 Da) with predominantly internal olefin placements. 3b and 4b copolymerize ethylene with methyl acrylate to linear copolymers that contain up to 11.7 mol % methyl acrylate, which is incorporated as -CH2CH(CO2Me)CH2- (80%) in-chain units and -CH2CH(CO2Me)Me (8%) and -CH2CH=CH(CO2Me) (12%) chain-end units. 3b and 4b also copolymerize ethylene with vinyl fluoride to linear copolymers that contain up to 0.41 mol % vinyl fluoride, which is incorporated as -CH2CHFC2-, (similar to 80%) in-chain units and -CH2CF2H (7%), -CH2CHFCH3 (5%), and -CH2CH2F (8%) chain-end units. Complexes 3b and 4b are more stable and active in ethylene polymerization than analogous (PAr2-CH2CH2SO3)PdR catalysts, but are less active than analogous (PAr2-arenesulfonate)PdR catalysts. Low temperature NMR studies show that 4b reacts with ethylene below -10 degrees C to form the ethylene adduct cis-P,R(2b)PdMe(ethylene) (7b), which undergoes ethylene. insertion at 5 degrees C. DFT calculations for a model (PMe2-cyclopentanesulfonate)Pd(Pr)(ethylene) species show that ethylene insertion proceeds by cis-P,R/trans-P,R isomerization followed by migratory insertion, and that the lower activity of 3b and 4b vis-a-vis analogous (PAr2-arenesulfonate)PdR catalysts results from a higher barrier for migratory insertion of the trans-P,R isomer.