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Cationic Alkyl Complexes of the Rare‐Earth Metals: Synthesis, Structure, and Reactivity
Author(s) -
Arndt Stefan,
Okuda Jun
Publication year - 2005
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200404269
Subject(s) - chemistry , alkyl , cationic polymerization , lewis acids and bases , reactivity (psychology) , electrophile , polymerization , context (archaeology) , cyclopentadienyl complex , substituent , polymer chemistry , catalysis , medicinal chemistry , organic chemistry , medicine , paleontology , polymer , alternative medicine , pathology , biology
Cationic alkyl complexes of the rare‐earth metals [LnR m (L) n ] (3–m)+ (R=alkyl; m=1, 2; L=Lewis base) were virtually unknown species until recently. Because of their increased Lewis acidity/electrophilicity they should have considerable potential as homogeneous catalysts in olefin polymerization and in organic transformations. They can be generated by treating the neutral rare‐earth metal precursors containing at least two alkyl groups R with suitable Lewis or Brønsted acids in the presence of weakly coordinating anions. Not only monocationic but also dicationic alkyl derivatives have been shown to be accessible. In the context of modeling homogeneous ethylene polymerization using a mixture consisting of LnR 3 /AlR 3 /[NMe 2 HPh][B(C 6 F 5 ) 4 ], such dications were discovered. Some thermally robust examples of mono‐ and dicationic alkyl complexes have been structurally characterized as solvent‐separated ion pairs. Neutral and monoanionic macrocycles such as crown ethers or aza‐crown ethers as well as amidinato, β‐diketiminato, and substituted cyclopentadienyl ligands are suitable ancillary ligands to stabilize the cationic alkyl fragments.