Rare earth metal bis(amide) complexes bearing amidinate ancillary ligands: Synthesis, characterization, and performance as catalyst precursors for cis-1,4 selective polymerization of isoprene

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Abstract
A family of rare earth metal bis(amide) complexes bearing monoanionic amidinate [RC(N-2,6-Me2C6H3)2]− (R = cyclohexyl (Cy), phenyl (Ph)) as ancillary ligands were synthesized and characterized. One-pot salt metathesis reaction of anhydrous LnCl3 with one equivalent of amidinate lithium [RC(N-2,6-Me2C6H3)2]Li, following the introduction of two equivalents of NaN(SiMe3)2 in THF at room temperature afforded the neutral and unsolvated mono(amidinate) rare earth metal bis(amide) complexes [RC(N-2,6-Me2C6H3)2]Y[N(SiMe3)2]2 (R = Cy (1); R = Ph (2)), and the “ate” mono(amidinate) rare earth metal bis(amide) complex [CyC(N-2,6-Me2C6H3)2]Lu[N(SiMe3)2]2(μ-Cl)Li(THF)3 (3) in 61–72% isolated yields. These complexes were characterized by elemental analysis, NMR spectroscopy, FT-IR spectroscopy, and X-ray single crystal diffraction. Single crystal structural determination revealed that the central metal in complexes 1 and 2 adopts a distorted tetrahedral geometry, and in complex 3 forms a distorted trigonal bipyramidal geometry. In the presence of AlMe3 , and in combination with one equimolar amount of [Ph3C][B(C6F5)4], complexes 1 and 2 showed high activity towards isoprene polymerization to give high molecular weight polyisoprene (Mn > 104) with good cis-1,4 selectivity (>90%).

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