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Borane and Borohydride Complexes of the Rare‐Earth Elements: Synthesis, Structures, and Butadiene Polymerization Catalysis
Author(s) -
Jenter Jelena,
Meyer Nils,
Roesky Peter W.,
Thiele Sven K.H.,
Eickerling Georg,
Scherer Wolfgang
Publication year - 2010
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.200902923
Subject(s) - chemistry , borohydride , ligand (biochemistry) , lanthanide , coordination sphere , borane , molecule , schiff base , reactivity (psychology) , metal , medicinal chemistry , crystallography , catalysis , inorganic chemistry , stereochemistry , crystal structure , ion , organic chemistry , biochemistry , receptor , medicine , alternative medicine , pathology
The reaction of potassium 2,5‐bis[ N ‐(2,6‐diisopropylphenyl)iminomethyl]pyrrolyl [(dip 2 ‐pyr)K] with the borohydrides of the larger rare‐earth metals, [Ln(BH 4 ) 3 (thf) 3 ] (Ln=La, Nd), afforded the expected products [Ln(BH 4 ) 2 (dip 2 ‐pyr)(thf) 2 ]. As usual, the trisborohydrides reacted like pseudohalide compounds forming KBH 4 as a by‐product. To compare the reactivity with the analogous halides, the dimeric neodymium complex [NdCl 2 (dip 2 ‐pyr)(thf)] 2 was prepared by reaction of [(dip 2 ‐pyr)K] with anhydrous NdCl 3 . Reaction of [(dip 2 ‐pyr)K] with the borohydrides of the smaller rare‐earth metals, [Sc(BH 4 ) 3 (thf) 2 ] and [Lu(BH 4 ) 3 (thf) 3 ], resulted in a redox reaction of the BH 4 − group with one of the Schiff base functions of the ligand. In the resulting products, [Ln(BH 4 ){(dip)(dip‐BH 3 )‐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 BH 4 − anion with the Schiff base function (a BH 3 molecule) is trapped in a unique reaction mode in the coordination sphere of the metal complex. The BH 3 molecule coordinates in an η 2 fashion to the metal atom. The rare‐earth‐metal atoms are surrounded by the η 2 ‐coordinated BH 3 molecule, the η 3 ‐coordinated BH 4 − 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(BH 4 ){(dip)(dip‐BH 3 )‐pyr}(thf) 2 ]. The (DIP 2 ‐pyr) − borohydride and chloride complexes of neodymium, [Nd(BH 4 ) 2 (dip 2 ‐pyr)(thf) 2 ] and [NdCl 2 (dip 2 ‐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.