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Genuine Heteroleptic Complexes of Early Rare‐Earth Metals: Synthesis, X‐ray Structure, and Their Use for Stereospecific Isoprene Polymerization Catalysis
Author(s) -
Bonnet Fanny,
Visseaux Marc,
BarbierBaudry Denise,
Vigier Estelle,
Kubicki Marek M.
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305595
Subject(s) - isoprene , chemistry , polymerization , stereospecificity , steric effects , lanthanide , samarium , bimetallic strip , catalysis , crystal structure , crystallography , polymer chemistry , stereochemistry , medicinal chemistry , polymer , inorganic chemistry , organic chemistry , copolymer , ion
Abstract Genuine heteroleptic neodymium and samarium complexes of formula [Cp*′Ln{( p ‐tol)NN}(BH 4 )] (Cp*′ = C 5 Me 4 ( n Pr), ( p ‐tol)NN = ( p ‐tol)NC(Me)CHC(Me)N( p ‐tol), Ln = Sm: 1 a , Ln = Nd: 1 b ) 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 1 H 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)] ( 2 b ) was only obtained as a part of a mixture. Analysis of crystals of 2 b by X‐ray diffraction revealed a molecular structure very similar to that of 1 a . 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.