Rare earth metal bis(alkyl) complexes bearing amino phosphine ligands: Synthesis and catalytic activity toward ethylene polymerization

Reactions of neutral amino phosphine compounds HL1–3 with rare earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2, afforded a new family of organolanthanide complexes, the molecular structures of which are strongly dependent on the ligand framework. Alkane elimination reactions between 2-(CH3NH)-C6H4P(Ph)2 (HL1) and Lu(CH2SiMe3)3(THF)2 at room temperature for 3 h generated mono(alkyl) complex (L1)2Lu(CH2SiMe3)(THF) (1). Similarly, treatment of 2-(C6H5CH2NH)-C6H4P(Ph)2 (HL2) with Lu(CH2SiMe3)3(THF)2 afforded (L2)2Lu(CH2SiMe3)(THF) (2), selectively, which gradually deproportionated to a homoleptic complex (L2)3Lu (3) at room temperature within a week. Strikingly, under the same condition, 2-(2,6-Me2C6H3NH)-C6H4P(Ph)2 (HL3) swiftly reacted with Ln(CH2SiMe3)3(THF)2 at room temperature for 3 h to yield the corresponding lanthanide bis(alkyl) complexes L3Ln(CH2SiMe3)2(THF)n (4a: Ln = Y, n = 2; 4b: Ln = Sc, n = 1; 4c: Ln = Lu, n = 1; 4d: Ln = Yb, n = 1; 4e: Ln = Tm, n = 1) in high yields. All complexes have been well defined and the molecular structures of complexes 1, 2, 3 and 4b–e were confirmed by X-ray diffraction analysis. The scandium bis(alkyl) complex activated by AlEt3 and [Ph3C][B(C6F5)4], was able to catalyze the polymerization of ethylene to afford linear polyethylene.

Graphical abstractA series of amido phosphine ligated rare earth metal mono-, bis-(alkyl) and homoleptic complexes have been prepared. The molecular structures and catalytic activity of the resultant complexes have shown significant dependence on rigidity and sterics of the ligand framework. The scandium bis(alkyl) complex upon activation with cocatalyst [Ph3C][B(C6F5)4]/aluminum triethyls, has exhibited various activity toward ethylene polymerization under different polymerization conditions to afford linear polyethylene.Figure optionsDownload full-size imageDownload as PowerPoint slide