Cationic Palladium(II) Complexes of Phosphine–Sulfonamide Ligands: Synthesis, Characterization, and Catalytic Ethylene Oligomerization

A series of cationic palladium­(II)
complexes bearing phosphine–sulfonamide ligands, [(P,O)­PdMe­(lutidine)]­[SbF6], were synthesized and used for catalytic ethylene oligomerization.
The molecular structure of the complex {[N,N-dicyclohexyl-2-(diphenylphosphanyl)­benzenesulfonamide]­PdMe­(lutidine)}­[SbF6] shows that the phosphorus atom and the oxygen atom coordinate
to the palladium center. The ethylene oligomerization behavior is
greatly influenced by the phosphino substituents, while the substituents
on sulfonamide show only minimal effects. Complexes containing the
diphenylphosphanyl group are highly selective for ethylene dimerization,
affording 1-butene exclusively with moderate activity. The bulkier
bis­(2-methoxyphenyl)­phosphanyl group leads to higher activity and
gives α-olefins containing mainly 1-butene and 1-hexene, with
a 1-hexene content of up to 35%. The palladium complexes bearing alkyl
phosphino substituents give 1-butene and 1-hexene as the major products;
a small amount of 2-butene (<5%) was observed, suggesting the occurrence
of chain walking. The addition of B­(C6F5)3 greatly enhances the catalytic activity. Experimental results
suggest that the increase in activity is likely due to the abstraction
of lutidine, not from the coordination of B­(C6F5)3 to the sulfonamide oxygen atom.