Methylnickel compounds containing 2-phosphinylethanolato ligands – Syntheses, properties, and ethene coupling reactions

Combining dimethylphosphinylethanols HO(R1R2)CCH2PMe2 (1: R1 = R2 = C6H5; 2: R1 = R2 = 4-OMe–C6H4; 5: R1 = R2 = 4-NMe2–C6H4) with methyl(methoxo)(trimethylphosphine)nickel gave mononuclear methyl(trimethylphosphine)nickel(chelate) compounds 7–9. Ligand 6 (R1 = Me, R2 = 4-OMe–C6H5) afforded a dinuclear methylnickel compound 14. By reacting (TMEDA)lithium-dimethylphosphinylmethanide with ketones OC(R1R2), the dimethylphosphinylethanols HO(R1R2)CCH2PMe2 (3: R1R2 = 9-fluorenyl; 4: R1 = H, R2 = C6H5) were synthesized as prechelate ligands. Under otherwise similar conditions, the fluorenyl substituted anion in 3 gave rise to a mononuclear complex 10 which was found to act as a source of trimethylphosphine forming dinuclear 11 and at the same time to act as an acceptor of trimethylphosphine forming pentacoordinate 10 · PMe3. Ni(COD)(PMe3)2 was used as a scavenger of PMe3 in converting 8 or 9 to the dinuclear methylnickel compounds 12 and 13, respectively. Modifying the P,O chelating unit of a methyl nickel compound by introducing 2-phosphinylethanolato ligands leads to novel single-component catalysts for ethene oligomerization showing moderate reactivity and thermal stability.

Anionic [P,O]-ligands derived from dimethylphosphinylethanols in methylnickel complexes form five-membered nickelacycles in square planar geometry, which catalyze the polymerization of ethene with moderate activity. Supporting trimethylphosphine ligands are dissociated by switching to the [P,μ-O]-coordination mode in dinuclear compounds. The first dinickel complex acting as a source of a single-component catalyst was characterized by X-ray analysis.Figure optionsDownload as PowerPoint slide