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Bifunctional rhenium complexes for the catalytic transfer-hydrogenation reactions of ketones and imines


Landwehr, Anne; Dudle, Balz; Fox, Thomas; Blacque, Olivier; Berke, Heinz (2012). Bifunctional rhenium complexes for the catalytic transfer-hydrogenation reactions of ketones and imines. CHEMISTRY-A EUROPEAN JOURNAL, 18(18):5701-5714.

Abstract

The silyloxycyclopentadienyl hydride complexes Re(H)(NO)(PR3)(C5H4OSiMe2tBu)] (R=iPr (3?a), Cy (3?b)) were obtained by the reaction of Re(H)(Br)(NO)(PR3)2] (R=iPr, Cy) with LiC5H4OSiMe2tBu]. The ligandmetal bifunctional rhenium catalysts Re(H)(NO)(PR3)(C5H4OH)] (R=iPr (5?a), Cy (5?b)) were prepared from compounds 3?a and 3?b by silyl deprotection with TBAF and subsequent acidification of the intermediate salts Re(H)(NO)(PR3)(C5H4O)]NBu4] (R=iPr (4?a), Cy (4?b)) with NH4Br. In nonpolar solvents, compounds 5?a and 5?b formed an equilibrium with the isomerized trans-dihydride cyclopentadienone species Re(H)2(NO)(PR3)(C5H4O)] (6?a,b). Deuterium-labeling studies of compounds 5?a and 5?b with D2 and D2O showed H/D exchange at the HRe and HO positions. Compounds 5?a and 5?b were active catalysts in the transfer hydrogenation reactions of ketones and imines with 2-propanol as both the solvent and H2 source. The mechanism of the transfer hydrogenation and isomerization reactions was supported by DFT calculations, which suggested a secondary-coordination-sphere mechanism for the transfer hydrogenation of ketones.

Abstract

The silyloxycyclopentadienyl hydride complexes Re(H)(NO)(PR3)(C5H4OSiMe2tBu)] (R=iPr (3?a), Cy (3?b)) were obtained by the reaction of Re(H)(Br)(NO)(PR3)2] (R=iPr, Cy) with LiC5H4OSiMe2tBu]. The ligandmetal bifunctional rhenium catalysts Re(H)(NO)(PR3)(C5H4OH)] (R=iPr (5?a), Cy (5?b)) were prepared from compounds 3?a and 3?b by silyl deprotection with TBAF and subsequent acidification of the intermediate salts Re(H)(NO)(PR3)(C5H4O)]NBu4] (R=iPr (4?a), Cy (4?b)) with NH4Br. In nonpolar solvents, compounds 5?a and 5?b formed an equilibrium with the isomerized trans-dihydride cyclopentadienone species Re(H)2(NO)(PR3)(C5H4O)] (6?a,b). Deuterium-labeling studies of compounds 5?a and 5?b with D2 and D2O showed H/D exchange at the HRe and HO positions. Compounds 5?a and 5?b were active catalysts in the transfer hydrogenation reactions of ketones and imines with 2-propanol as both the solvent and H2 source. The mechanism of the transfer hydrogenation and isomerization reactions was supported by DFT calculations, which suggested a secondary-coordination-sphere mechanism for the transfer hydrogenation of ketones.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2012
Deposited On:04 Mar 2013 13:29
Last Modified:05 Apr 2016 16:34
Publisher DOI:https://doi.org/10.1002/chem.201103685

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