Premium
Homoleptic Rare‐Earth Metal(III) Tetramethylaluminates: Structural Chemistry, Reactivity, and Performance in Isoprene Polymerization
Author(s) -
Zimmermann Melanie,
Frøystein Nils Åge,
Fischbach Andreas,
Sirsch Peter,
Dietrich H. Martin,
Törnroos Karl W.,
Herdtweck Eberhardt,
Anwander Reiner
Publication year - 2007
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.200700534
Subject(s) - homoleptic , chemistry , lanthanide , isoprene , polymerization , metathesis , lanthanide contraction , alkyl , carboxylate , catalysis , praseodymium , metal , amide , polymer chemistry , stereochemistry , inorganic chemistry , organic chemistry , polymer , copolymer , ion
The complexes [Ln(AlMe 4 ) 3 ] (Ln=Y, La, Ce, Pr, Nd, Sm, Ho, Lu) have been synthesized by an amide elimination route and the structures of [Lu{(μ‐Me) 2 AlMe 2 } 3 ], [Sm{(μ‐Me) 2 AlMe 2 } 3 ], [Pr{(μ‐Me) 2 AlMe 2 } 3 ], and [La{(μ‐Me) 2 AlMe 2 } 2 {(μ‐Me) 3 AlMe}] determined by X‐ray crystallography. These structures reveal a distinct Ln 3+ cation size‐dependency. A comprehensive insight into the intrinsic properties and solution coordination phenomena of [Ln(AlMe 4 ) 3 ] complexes has been gained from extended dynamic 1 H and 13 C NMR spectroscopic studies, as well as 1D 89 Y, 2D 1 H/ 89 Y, and 27 Al NMR spectroscopic investigations. [Ce(AlMe 4 ) 3 ] and [Pr(AlMe 4 ) 3 ] have been used as alkyl precursors for the synthesis of heterobimetallic alkylated rare‐earth metal complexes. Both carboxylate and siloxide ligands can be introduced by methane elimination reactions that give the heterobimetallic complexes [Ln{(O 2 CAr i Pr ) 2 (μ‐AlMe 2 )} 2 (AlMe 4 )(C 6 H 14 ) n ] and [Ln{OSi(O t Bu) 3 }(AlMe 3 )(AlMe 4 ) 2 ], respectively. [Pr{OSi(O t Bu) 3 }(AlMe 3 )(AlMe 4 ) 2 ] has been characterized by X‐ray structure analysis. All of the cerium and praseodymium complexes are used as precatalysts in the stereospecific polymerization of isoprene (1–3 equivalents of Et 2 AlCl as co‐catalyst) and compared to the corresponding neodymium‐based initiators reported previously. The superior catalytic performance of the homoleptic complexes leads to quantitative yields of high‐ cis ‐1,4‐polyisoprene (>98 %) in almost all of the polymerization experiments. In the case of the binary catalyst mixtures derived from carboxylate or siloxide precatalysts quantitative formation of polyisoprene is only observed for n Ln : n Cl =1:2. The influence of the metal size is illustrated for the heterobimetallic lanthanum, cerium, praseodymium, neodymium, and gadolinium carboxylate complexes, and the highest activities are observed for praseodymium as a metal center in the presence of one equivalent of Et 2 AlCl.