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IAN Amines:  Chiral C2-Symmetric Zirconium(IV) Complexes from Readily Modified Axially Chiral C1-Symmetric β-Diketimines

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posted on 10.05.2004, 00:00 by Sarah B. Cortright, John C. Huffman, Ryan A. Yoder, Joseph N. Coalter, Jeffrey N. Johnston
A general synthesis of β-diketimines derived from Isoquinoline and AminoNaphthalene components (IAN amines) is reported. Beginning from inexpensive 2-naphthol and isoquinoline, the sequence of reactions leading to R-IAN amines is convergent, short, and high-yielding. Several new derivatives are reported (e.g., R = Bn, iPr, tBu, Ph, 2,6-Me2Ph, 2,6-iPr2Ph, 2-Np). All of these were complexed to zirconium(IV) by transamination with Zr(NMe2)4, and in all cases 1:1 R-IAN:Zr complexes immediately formed at 25 °C. Except in cases of severe steric hindrance (iPr-IAN and 2,6-Me2Ph), the corresponding 2:1 IAN:Zr complexes formed at temperatures ranging from 25 to 100 °C in toluene. A feature conserved among all 2:1 IAN:Zr complexes was a remarkable degree of diastereoselectivity favoring a C2-symmetric bis(β-diketiminate) isomer bearing cis-NMe2 and cis-pyridyl ligands. Although all complexations were performed from rac-IAN, the resulting complexes are composed solely of homochiral ligands. The configurational integrity of Me-IAN and its ability to transfer asymmetry upon metal coordination was demonstrated in the catalyzed enantioselective addition of diethylzinc to benzaldehyde. Given the topographical similarity between these and metallocene complexes, several derivatives were preliminarily evaluated in ethylene polymerization.