Tailoring of pyridylidene amidate (PYA) palladium complexes for ethylene conversion beyond dimerization and for the conversion of higher a-olefins.

Ethylene polymerization with late transition metals offers the possibility to include polar monomers for the generation of functionalized polymers. However, several palladium complexes, including those with pyridyl-functionalized pyridinium amidate (PYA) ligands [Pd(Me)(MeCN)(N,N′)]+ (with N = PYA, N′ = pyridyl) undergo rapid b-hydrogen elimination and form predominantly butene derivatives. Here we have modified a range of elements in the catalyst design, including (i) the PYA substituents (Me, Bu, CH2OCH3), (ii) the chelating imine donor, (iii) the labile neutral ligand L , and (iv) the non-coordinating anion. These variations indicated factors that prevent (L = lutidine) or slow down ethylene conversion (imine = oxalyl, triazolyl, pyrazolyl), and factors that accelerate it. In particular, the absence of MeCN as coordinating ligand and the introduction of BArF as counterion is highly beneficial and leads to efficient ethylene conversion and the formation of oligomers with C20–C30 chain length. Time-dependent reaction monitoring suggests a step-growth rather than the more common chain growth mechanism with the initial formation of butene and subsequent conversion of butene and higher olefins. Indeed, also higher a-olefins such as 1-hexene were oligomerized with this in-situ prepared catalytic PYA palladium system.