Structure−Reactivity Relationships of Amido-Pyridine-Supported Rare-Earth-Metal Alkyl Complexes

Treatment of rare-earth-metal dialkyl complexes with group 13 cocatalysts is a prominent approach to generate homogeneous catalysts active in olefin polymerization. Reaction of Ln(CH2SiMe3)3(THF)2 with monovalent imino-amido-pyridine [2-{(2,6-iPr2C6H3)NCMe}-6-{(2,6-iPr2C6H3)NHCMe2}C5H3N] (HL2) gives donor solvent-free discrete dialkyl compounds [L2]Ln(CH2SiMe3)2 (Ln = Sc, Y, Lu). In the solid state the scandium derivative is isostructural to the previously reported lutetium complex (Gordon et al.). Activation by borate cocatalysts [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4] produces ion pairs that polymerize ethylene in moderate yields (activity: Sc > Lu). Cationization with N-[tris(pentafluorophenyl)borane]-3H-indole gives inactive species. 1H/13C/11B/19F NMR spectroscopy is applied to examine the interaction of the rare-earth-metal dialkyl complexes with the boron cocatalysts. In contrast to the monoalkyl diamido-pyridine compounds [L1]Ln(CH2SiMe3)(THF)x (HL1 = [2,6-{(2,6-iPr2C6H3)NHCH2}C5H3N], the dialkyl imino-amido-pyridine complexes do not polymerize methyl methacrylate.