Synthesis, characterization, and reactivity studies in ethylene polymerization of cyclometalated palladium(II) complexes containing terdentate ligands with N,C,N-donors

Abstract

The reaction of [Na2PdCl4] with 3,5-bis(2-pyridoxy)toluene (LpyH) in acetic acid yields the cyclometalated complex [PdCl(Lpy-N, C, N)] (1). Complex 1 can be further converted into neutral species by metathesis reaction exchange of chloride by either iodide or thiocyanate to yield [PdX(Lpy-N, C, N)] (X = I (2), SCN (3)). The chloride can be replaced by neutral ligands like pyridine or acetonitrile in the presence of silver tetrafluoroborate to give the corresponding cationic compounds [PdL(Lpy-N, C, N)]BF4 (L = Py (4), MeCN (5)). In contrast, the reaction of [Na2PdCl4] with 3,5-bis(3, 5-dimethylpyrazol-1-ylmethyl)toluene (LpzH) under analogous conditions yields the neutral complex [PdCl2(LpzH-N, N)](6) with the ligand bidentate N,N-donor. The cyclometalated palladium complex [PdCl(Lpz-N, C, N)] (7) was prepared by the reaction of Pd(OAc)2 with LpzH in acetic acid followed by a metathetic reaction with lithium chloride in acetone/water. Complexes 1, 6, and 7 in the presence of methylaluminoxane (MAO) lead to an active catalyst for the polymerization of ethylene.