Lewis Acid Modification and Ethylene Oligomerization Behavior of Palladium Catalysts That Contain a Phosphine-Sulfonate-Diethyl Phosphonate Ancillary Ligand

The multifunctional phosphine-sulfonate-diethyl phosphonate ligand [1-(P­(4-tBu-Ph)­(2-PO3Et2-5-Me-Ph)-2-SO3-5-Me-Ph]− ([OP-P-SO]−) was used to form complexes of type [κ2-(OP-P-SO)]­PdMe­(L) (L = 2,6-lutidine, 2b; L = pyridine, 2c). B­(C6F5)3 abstracts the Pd-bound sulfonate group of 2b and induces a switch to a phosphine-diethyl phosphonate coordination mode, affording [κ2-(OP-P-SO-B­(C6F5)3)]­PdMe­(2,6-lutidine) (3). In contrast, MgCl2 binds to the sulfonate and diethyl phosphonate units of 2b, generating the dipalladium species [{κ2-(OP-P-SO)­PdMe}2­(μ-Cl)]­[MgCl] (4) by simple self-assembly. AgB­(C6F5)4 reacts with 4 in the presence of THF to selectively abstract the Mg-Cl to form [{κ2-(OP-P-SO)­PdMe}2­(μ-Cl)­Mg­(THF)]­[B­(C6F5)4] (5). The ethylene polymerization behaviors of 2b, 2c, 3, and 5 are quite similar (Mn: 120–1170 Da, activity: 60–290 kg (mol Pd)–1 h–1). All of these catalysts produce low-molecular-weight polyethylene with predominantly internal unsaturation, but little branching. The reaction of 4 with 2 equiv of AgB­(C6F5)4 to abstract both chloride ions generates an active ethylene polymerization catalyst that produces linear polyethylene with a bimodal molecular weight distribution.