Theo Zweifel, D. Scheschkewitz, T. Ott
Dec 1, 2009
Citations
0
Influential Citations
23
Citations
Journal
European Journal of Inorganic Chemistry
Abstract
Bis(olefin)amines (boas) are a new class of ligands for the synthesis of transition metal complexes, which can be used in various homogeneous catalytic reactions. A simple straightforward coupling reaction between 5H-dibenzo[a,d]cyclohepten-5-yl chloride (tropCl) and primary amines allows the synthesis of various chiral boas. Birch reduction of phenylalanine gives (2S)-2-amino-3-cyclohexa-1,4-dien-1-yl propanoate, which is used for the synthesis of the bis(olefin)amine methyl (2S)-3-(cyclohexa-1,4-dienyl)-2-(5H-dibenzo[a,d]cyclohepten-5-yl-amino)propionate. Coupling between cyclohex-3-en-1-ylamine with tropCl gives N-(cyclohex-3′-en-1′-yl)-5H-dibenzo[a,d]cyclohepten-5-ylamine, which was separated into its enantiomers. Bicyclic cyclohexenylamine derivatives like bicyclo[2.2.2]oct-5-en-2-ylamine and 2-(methoxycarbonyl)bicyclo[2.2.1]hept-5-en-3-ylamine were likewise coupled with tropCl to give chiral bis(olefin)amines. Alternatively, 5H-dibenzo[a,d]cyclohepten-5-ylamine (tropNH2) can react with cyclohexenyl ketones to give prochiral bis(olefin)imines, which were reduced to the corresponding bis(olefin)amines. With [Rh2(μ-Cl)2(CO)4] or [Rh2(μ-Cl)2(C2H4)4], a complexation of these compounds was achieved leading to chiral rhodium complexes of the type [Rh(boa)(CO)]OTf or [Rh(boa)(PR3)]OTf. The complexes have a strongly distorted saw-horse-type structure (determined by X-ray diffraction studies) and were tested in transfer hydrogenations with ethanol/2-propanol as hydrogen donor. Only complexes with tightly bound olefinic binding sites and a pronounced saw-horse-type structure give significant activities. Furthermore, a phosphane ligand in trans position to the coordinated amine function has a positive impact of the catalysts performance. None of the investigated catalysts gave an impressive enantiomeric excess (ee < 60 %) in the transfer hydrogenation of acetophenone.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)