Nickel and Palladium Complexes of Pyridine−Phosphine Ligands as Ethene Oligomerization Catalysts

Abstract

Pyridine−phosphine ligands 1−5 have been used to prepare neutral nickel dichloride complexes, neutral methylpalladium chloride complexes, and cationic methylpalladium complexes. The ligands consist of a diphenylphosphine and a pyridine moiety and differ in the backbone connecting those donor groups. Nickel complexes 9−13 are paramagnetic complexes, and they were characterized by elemental analysis, high-resolution mass spectrometry, and, for 10 and 12, single-crystal X-ray diffraction. Neutral palladium complexes 14−18 were fully characterized. Single-crystal X-ray diffraction was performed on complexes 15 and 16, and variable-temperature NMR demonstrated that 16 exhibits slow inversion of the metallacycle. Cationic palladium species 19−23 were obtained from the neutral complexes after chloride abstraction. Like its neutral precursor, 21 showed slow ring inversion. The nickel species were evaluated as ethene oligomerization catalysts after activation with MAO. All complexes were highly active, with TOFs between 24 × 103 and 85 × 103 (mol C2H4)·(mol Ni·h)−1. Butenes were the major product in all cases, forming 76 to 96 mol % of the product. Selectivities for 1-butene were between 10% and 40%. The cationic palladium species showed a very low productivity for ethene oligomerization, with TOFs ≤16 (mol C2H4)·(mol Pd·h)−1 and 38 to 88 mol % butenes as the main product.