Neutral chloromethylpalladium(II) complexes, [Pd(Cl)(CH₃)(L)] (1a–5a) with ligands κ²-N^S-2-((3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl)-6-(phenylthiomethyl)pyridine (L1), κ²-N^S-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenylthiomethyl)pyridine (L2), κ²-N^Se-2-((3,5-di-tert-butyl-1H-pyrazol-1-yl)methyl)-6-(phenylselanylmethyl)pyridine (L3), κ²-N^Se-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenylselanylmethyl)pyridine (L4), and κ²-N^N-2-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-6-(phenoxymethyl)pyridine (L5) have been synthesised and characterised by various spectroscopic techniques. Ligands L1–L4 exhibit N_py^S/Se bidentate coordination whereas L5 shows an N_py^N_pz bidentate coordination mode in their corresponding neutral palladium complexes. Abstraction of chloride in neutral palladium complexes with NaBAr₄ (BAr₄ = tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate) resulted in the formation of the cationic palladium complexes 1b–5b, in which L1–L4 adopt a tridentate N_pz^N_py^X (X = S or Se) coordination mode in their respective cationic palladium complexes (1b–4b) whilst L5 in complex 5b adopts a N_py^N_pz bidentate coordination mode and the palladium centre is stabilized by the weakly coordinating acetonitrile. Compounds 1b–5b readily undergo CO insertion into the Pd–CH₃ bond to form Pd–acyl that determines their ability to catalyse CO/ethylene copolymerisation to polyketones.