Genuine Heteroleptic Complexes of Early Rare-Earth Metals: Synthesis, X-ray Structure, and Their Use for Stereospecific Isoprene Polymerization Catalysis

• Published in: Chemistry : a European journal Vol. 10; no. 10; pp. 2428 - 2434
• Main Authors: Bonnet, Fanny, Visseaux, Marc, Barbier-Baudry, Denise, Vigier, Estelle, Kubicki, Marek M.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 17.05.2004; WILEY‐VCH Verlag; Wiley
• Subjects: borohydrides; catalysis; Chemistry; Chemistry, Multidisciplinary; neodymium; Physical Sciences; polymerization; samarium; Science & Technology; borohydrides; polymerization; samarium; HYDRIDES; REACTIVITY; ORGANOLANTHANIDES; catalysis; CRYSTAL-STRUCTURES; MIXED-LIGAND; neodymium; DIKETIMINATE LIGANDS; COPOLYMERIZATION; DERIVATIVES; PRECURSORS
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200305595

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: 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 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)] (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. The real thing! Genuine heteroleptic early rare‐earth metal complexes of general formula [Cp*′Ln{(p‐tol)NN}(X)] (Cp*′ = C5Me4nPr, (p‐tol)NN = (p‐tol)NC(Me)CHC(Me)N(p‐tol), X = BH4, Ln = Sm (1; see structure), Nd; X = Cl, Ln = Nd) have been obtained for the first time. In the presence of an alkylmagnesium activator, 1 behaves as an efficient and highly trans‐specific catalyst for the polymerization of isoprene.