Enhancement of Chain Growth and Chain Transfer Rates in Ethylene Polymerization by (Phosphine-sulfonate)PdMe Catalysts by Binding of B(C6F5)3 to the Sulfonate Group

Binding of B(C6F5)(3) to a sulfonate oxygen of (orthophosphino-arenesulfonate)PdR catalysts results in a 3-4 fold increase in the rate of chain growth and a larger increase in the rate of chain transfer. The reaction of (PO-Et)PdMe(py) (1a, [PO-Et](-) = ortho-{(2-Et-Ph)(2)P}-para-toluenesulfonate) with 1 equiv of B(C6F5)(3) yields the base-free dimer {(PO-Et)PdMe}(2) (2a), in which the (PO-Et)PdMe units are linked through an eight-membered [PdSO2](2) ring. The reaction of ((PO-3,5-'Bu-2)PdMe}(2)(TMEDA) (4b; [PO-3,5-Bu-t(2)](-) = ortho-{(3,5-(Bu2-Ph)-Bu-t)(2)P}-para-toluenesulfonate, TMEDA = N,N,N',N'-tetramethylethylenediamine) with BF3.Et2O yields the soluble base-free dimer {(PO-3,5-Bu-t(2))PdMe}(2) (2b), in which the (PO-3,5-Bu-t(2))PdMe units are linked through a four-membered Pd2O2 ring. 2b reacts with 2 equiv of B(C6F5)(3) to yield {[PO.B(C6F5)(3)-3,5-Bu-t(2)]PdMe}(2) (5b, [PO.B(C6F5)(3)-3,5-Bu-t(2)](-) = [2-{(3,5-Bu-t(2)-Ph)(2)P}-4-Me-C6H3SO2OB(C6F5)(3)](-)), which crystallizes from Et2O as the monomeric complex [POB(C6F5)(3)-3,5-Bu-t(2)]PdMe(Et2O) (6b). In both 5b and 6h, the B(C6F5)(3) binds to a sulfonate oxygen. In toluene solution at 60 degrees C, 2h polymerizes ethylene (80 psi) to linear polyethylene with M-n = 3,000, while the B(C6F5)(3) adducts 5b and 6h yield ethylene oligomers (M-n = 160-170). 5b and 6h are 3-4 times more active than 2h. Similarly, la polymerizes ethylene to linear polyethylene with M-n = 29,300 (toluene, 80 degrees C, 435 psi), while la-4 B(C6F5)(3) yields polymer with M-n = 2,520 with a 4 fold increase in activity. 2b reacts with ethylene at 7 degrees C to form the ethylene adduct (PO-3,5-Bu-t(2))PdMe(CH2=CH2) (7b) followed by multiple insertions to generate (PO-3,5-Bu-t(2))Pd(CH2CH2)(n)CH3 species. In contrast, 5b reacts with ethylene to form [POB(C6F5)(3)-3,5-Bu-t(2)]PdMe(CH2=CH2) (8b) followed by insertion and, beta-H transfer to yield propene with subsequent catalytic formation of 1-butene and higher olefins. The rate of ethylene insertion of 8b is 3 times greater than that of 7b, consistent with the batch polymerization results. The polymer yield and molecular weight data show that binding of B(C6F5)(3) to 2b and la increases the chain transfer rates by a factor of 80 and 42, respectively.