Nickel and Palladium Complexes of New Pyridine-Phosphine Ligands and Their Use in Ethene Oligomerization

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• 作者：Jitte Flapper ; Huub Kooijman ; Martin Lutz ; Anthony L. Spek ; Piet W. N. M. van Leeuwen ; Cornelis J. Elsevier ; Paul C. J. Kamer
• 刊名：Organometallics
• 出版年：2009
• 出版时间：June 8, 2009
• 年：2009
• 卷：28
• 期：11
• 页码：3272-3281
• 全文大小：226K
• 年卷期：v.28,no.11(June 8, 2009)
• ISSN：1520-6041

文摘

New pyridine-phosphine ligands of general structure 2-[2-(diarylphosphino)ethyl]pyridine were developed. The phosphorus substituents in these bidentates are 2-tolyl, 2-anisyl, and mesityl. The ligands could be conveniently synthesized in good yields. The nickel dichloride complexes of the ligands are paramagnetic. The metal centers have a distorted tetrahedral geometry, as was evident from the crystal structures and the magnetic moments in solution. The neutral methylpalladium chloride and the cationic methylpalladium complexes have a distorted square-planar geometry around the metal center. For the complexes of two of the ligands, an anagostic C−H···Pd interaction of a ligand-proton with the palladium atom was observed in the crystal structures and in solution. These interactions probably were related to hindered inversion of the six-membered metallocycle, which was observed in VT-NMR measurements. The complexes of the mesityl-substituted ligand show neither hindered inversion of the metal chelate ring nor a sign of Pd···H interactions. The nickel complexes form active catalysts for the oligomerization of ethene after MAO activation. The bulky 2-tolyl and mesityl groups suppress isomerization of the growing chain, reflected in a high 1-butene selectivity. For the complex made from the ligand with the most bulky (mesityl) substituents, this selectivity was 90%. The anisyl substituents induced a different catalytic behavior of the corresponding nickel complex. Selectivity for 1-butene was lower, but the productivity was higher, with a turnover frequency of 65 × 10³ (mol C₂H₄)·(mol Ni·h)⁻¹. The cationic palladium complexes showed a very low activity in ethene oligomerization. Butenes were the major product, but significant amounts of higher olefins were formed as well.