American Chemical Society
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Synthesis of Copper(I) Complexes Containing Enantiopure Pybox Ligands. First Assays on Enantioselective Synthesis of Propargylamines Catalyzed by Isolated Copper(I) Complexes

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journal contribution
posted on 2009-12-07, 00:00 authored by María Panera, Josefina Díez, Isabel Merino, Eduardo Rubio, M. Pilar Gamasa
Dinuclear [Cu2(R-pybox)2][X]2 [X = PF6, R-pybox = 2,6-bis[4′-(S)-isopropyloxazolin-2′-yl]pyridine (S,S)-iPr-pybox (1), 2,6-bis[4′-(R)-phenyloxazolin-2′-yl]pyridine) (R,R)-Ph-pybox (2), 2,6-bis[4′-(S)-isopropyl-5′,5′-difeniloxazolin-2′-yl]pyridine (S,S)-iPr-pybox-diPh (3); X = OTf, (R,R)-Ph-pybox (4)] and mononuclear complexes [Cu(R-pybox)2][PF6] [R-pybox = (S,S)-iPr-pybox (5), (R,R)-Ph-pybox (6)] have been diastereoselectively prepared by reaction of [Cu(MeCN)4][PF6] or CuOTf·0.5C6H6 and the corresponding pybox ligand. The reaction of CuX (X = I, Br, Cl) with substituted pybox in a 2:1 molar ratio allows us to synthesize tetranuclear complexes [Cu4X4(R-pybox}2] [R-pybox = (S,S)-iPr-pybox, X = I (7), Br (8); (R,R)-Ph-pybox, X = I (9), Br (10), Cl (11); (S,S)-iPr-pybox-diPh, X = I (12), Cl (13)]. Dinuclear complexes [Cu2(μ-Cl)(R-pybox)2][CuCl2] [R-pybox = (S,S)-iPr-pybox (15), (R,R)-Ph-pybox (16)] have been prepared by reaction of CuCl with iPr-pybox or Ph-pybox in 3:2 molar ratio. The structures of the complexes 1, 2, 7, 15, 16 and that of the polymeric species [Cu43-Br)3(μ-Br)(iPr-pybox)]n (14) have been determined by single-crystal X-ray diffraction analysis. Diffusion studies using 1H and 19F-DOSY experiments provide evidence that the different nuclearity of compounds 1 and 5 is maintained in the solution state and confirm that these ionic compounds exist in solution as stable, discrete, cationic complexes. The complexes 14, 6, 9, 10, and 16 as well as the previously reported [Cu2{(S,S)-iPr-pybox}2][OTf]2 have been assayed as catalysts in the enantioselective synthesis of propargylamines. The dinuclear complexes [Cu2{(R,R)-Ph-pybox}2][X]2 (2, 4) were found to be the most efficient catalysts (up to 89% e.e.).