Lewis Acid Modification and Ethylene Oligomerization
Behavior of Palladium Catalysts That Contain a Phosphine-Sulfonate-Diethyl
Phosphonate Ancillary Ligand
- Publication date
- Publisher
Abstract
The
multifunctional phosphine-sulfonate-diethyl phosphonate ligand
[1-(P(4-<sup><i>t</i></sup>Bu-Ph)(2-PO<sub>3</sub>Et<sub>2</sub>-5-Me-Ph)-2-SO<sub>3</sub>-5-Me-Ph]<sup>−</sup> ([OP-P-SO]<sup>−</sup>) was used to form complexes of type
[κ<sup>2</sup>-(OP-<i>P</i>-S<i>O</i>)]PdMe(L)
(L = 2,6-lutidine, <b>2b</b>; L = pyridine, <b>2c</b>).
B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> abstracts the Pd-bound sulfonate
group of <b>2b</b> and induces a switch to a phosphine-diethyl
phosphonate coordination mode, affording [κ<sup>2</sup>-(<i>O</i>P-<i>P</i>-SO-B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>)]PdMe(2,6-lutidine) (<b>3</b>). In contrast,
MgCl<sub>2</sub> binds to the sulfonate and diethyl phosphonate units
of <b>2b</b>, generating the dipalladium species [{κ<sup>2</sup>-(OP-<i>P</i>-S<i>O</i>)PdMe}<sub>2</sub>(μ-Cl)][MgCl] (<b>4</b>) by simple self-assembly.
AgB(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub> reacts with <b>4</b> in the presence of THF to selectively abstract the Mg-<i>Cl</i> to form [{κ<sup>2</sup>-(OP-<i>P</i>-S<i>O</i>)PdMe}<sub>2</sub>(μ-Cl)Mg(THF)][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>5</b>). The ethylene
polymerization behaviors of <b>2b</b>, <b>2c</b>, <b>3</b>, and <b>5</b> are quite similar (<i>M</i><sub>n</sub>: 120–1170 Da, activity: 60–290 kg (mol
Pd)<sup>–1</sup> h<sup>–1</sup>). All of these catalysts
produce low-molecular-weight polyethylene with predominantly internal
unsaturation, but little branching. The reaction of <b>4</b> with 2 equiv of AgB(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub> to abstract
both chloride ions generates an active ethylene polymerization catalyst
that produces linear polyethylene with a bimodal molecular weight
distribution
