title: Genuine heteroleptic complexes of early rare-earth metals: synthesis, X-ray structure, and their use for stereospecific isoprene polymerization catalysis.
abstract: Genuine heteroleptic neodymium and samarium complexes of formula [Cp*'Ln[(p-tol)NN](BH4)] (Cp*' = C5Me4(nPr), (p-tol)NN = (p-tol)NC(Me)CHC(Me)N(p-tol), Ln = Sm: 1a, Ln = Nd: 1b) have been synthesized for the first time. These unprecedented homologues of early lanthanocenes are prepared by a metathetic reaction between their monocyclopentadienylbisborohydrido precursors with the corresponding potassium diketiminate. Both complexes were obtained in good yields and were characterized by 1H NMR spectroscopy and elemental analysis. Complex 1 a has an non-solvated dimeric structure, as indicated by its crystallographic data. The chloroneodymium analogue [Cp*'Nd[(p-tol)NN](Cl)] (2b) was only obtained as a part of a mixture. Analysis of crystals of 2b by X-ray diffraction revealed a molecular structure very similar to that of 1a. Preliminary isoprene polymerization experiments were carried out with 1 b in the presence of an alkylmagnesium coactivator. The resulting bimetallic Nd/Mg system behaves as an efficient and highly stereospecific catalyst with the synthesis of trans-1,4-polyisoprene with more than 98% regularity. The control of the polymer structure is related to the steric hindrance around the lanthanide atom.
authors.affiliation: Laboratoire de Synthèse et d'Electrosynthèse Organométalliques, Crystallography Group, CNRS UMR 5188, Université de Dijon, 9 Avenue A. Savary, BP 47870, 21078 Dijon, France.
authors.forename: Fanny
authors.initials: F
authors.lastname: Bonnet
authors.forename: Marc
authors.initials: M
authors.lastname: Visseaux
authors.forename: Denise
authors.initials: D
authors.lastname: Barbier-Baudry
authors.forename: Estelle
authors.initials: E
authors.lastname: Vigier
authors.forename: Marek M
authors.initials: MM
authors.lastname: Kubicki