Borane and Borohydride Complexes of the Rare‐Earth Elements: Synthesis,Structures, and Butadiene Polymerization Catalysis |
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| Authors: | Jelena Jenter Dipl‐Chem Nils Meyer Dr Peter?W Roesky Prof?Dr Sven K‐H Thiele Dr Georg Eickerling Dr Wolfgang Scherer Prof?Dr |
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| Institution: | 1. Institut für Anorganische Chemie, Karlsruher Institut für Technologie (KIT), Engesserstr. 15, 76131 Karlsruhe (Germany), Fax: (+49)?721‐608‐4845;2. Institut für Chemie und Biochemie, Freie Universit?t Berlin, Fabeckstrasse 34–36, 14195 Berlin (Germany);3. Dow Olefinverbund GmbH, Synthetic Rubber Business, Site Schkopau, Building F 7, 06258 Schkopau (Germany);4. Institut für Physik, Universit?t Augsburg, Universit?tsstr. 1, 86159 Augsburg (Germany), Fax: (+49)?821‐598‐3227 |
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| Abstract: | The reaction of potassium 2,5‐bisN‐(2,6‐diisopropylphenyl)iminomethyl]pyrrolyl (dip2‐pyr)K] with the borohydrides of the larger rare‐earth metals, Ln(BH4)3(thf)3] (Ln=La, Nd), afforded the expected products Ln(BH4)2(dip2‐pyr)(thf)2]. As usual, the trisborohydrides reacted like pseudohalide compounds forming KBH4 as a by‐product. To compare the reactivity with the analogous halides, the dimeric neodymium complex NdCl2(dip2‐pyr)(thf)]2 was prepared by reaction of (dip2‐pyr)K] with anhydrous NdCl3. Reaction of (dip2‐pyr)K] with the borohydrides of the smaller rare‐earth metals, Sc(BH4)3(thf)2] and Lu(BH4)3(thf)3], resulted in a redox reaction of the BH4? group with one of the Schiff base functions of the ligand. In the resulting products, Ln(BH4){(dip)(dip‐BH3)‐pyr}(thf)2] (Ln=Sc, Lu), a dinegatively charged ligand with a new amido function, a Schiff base, and the pyrrolyl function is bound to the metal atom. The by‐product of the reaction of the BH4? anion with the Schiff base function (a BH3 molecule) is trapped in a unique reaction mode in the coordination sphere of the metal complex. The BH3 molecule coordinates in an η2 fashion to the metal atom. The rare‐earth‐metal atoms are surrounded by the η2‐coordinated BH3 molecule, the η3‐coordinated BH4? anion, two THF molecules, and the nitrogen atoms from the Schiff base and the pyrrolyl function. All new compounds were characterized by single‐crystal X‐ray diffraction. Low‐temperature X‐ray diffraction data at 6 K were collected to locate the hydrogen atoms of Lu(BH4){(dip)(dip‐BH3)‐pyr}(thf)2]. The (DIP2‐pyr)? borohydride and chloride complexes of neodymium, Nd(BH4)2(dip2‐pyr)(thf)2] and NdCl2(dip2‐pyr)(thf)]2, were also used as Ziegler–Natta catalysts for the polymerization of 1,3‐butadiene to yield poly(cis‐1,4‐butadiene). Very high activities and good cis selectivities were observed by using each of these complexes as a catalyst in the presence of various cocatalyst mixtures. |
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| Keywords: | boron chelates N ligands polymerization rare earths |
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