www.elsevier.nl/locate/jorganchem Journal of Organometallic Chemistry 621 (2001) 120 – 129 Synthesis of achiral, but unsymmetric, seven-membered rhodium(I)-chelates for hydrogenation in the chiral environment of alkyl polyglucoside micelles V. Fehring a , R. Kadyrov a , M. Ludwig a , J. Holz a , K. Haage b , R. Selke a, * a Institut fu ¨r Organische Katalyseforschung an der Uniersita ¨t Rostock, e.V., Buchbinderstr. 5 -6, D18055 Rostock, Germany b Max -Planck -Institut fu ¨r Kolloid - und Grenzfla ¨chenforschung, Abteilung Grenzfla ¨chen, Am Mu ¨hlenberg 2, Golm, D-14424 Potsdam, Germany Received 1 August 2000; received in revised form 14 September 2000; accepted 21 September 2000 Dedicated to Professor H. Brunner on the occasion of his 65th birthday Abstract Chiral rhodium(I) chelates containing a seven-membered ring are well-known active catalysts for the asymmetric hydrogenation of amino acid precursors. A high conformational flexibility allows their enantioselectivity to be strongly influenced by modifiers. Now we show the nature of the counter-ions to have a large influence in apolar solvents. In addition, the presence of micelle forming alkyl polyglycosides as amphiphiles causes a remarkable increase in the enantiomeric excess (%ee). However, on achiral catalysts this enantioselectivity inducing effect scarcely exceeds the standard deviation for the gas chromatographic determination of the enantiomeric ratio. This is also true for the application of unsymmetric P,P -ligands such as 3-phosphinopropyl-phos- phinites or butane-1,4-diyl-bis(phosphines) carrying different P -aryl groups, for which synthetic routes are given. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Alkyl polyglycosides; Asymmetric hydrogenation; Counter-ions; Micelles; Rhodium(I) chelates; Unsymmetric bisphosphines 1. Introduction Following the ideas of Oehme et al. [1] we found by the addition of amphiphiles an impressive increase in the enantioselectivity in water for a large number of chiral rhodium(I) chelates as asymmetric hydrogenation catalysts [2]. Recent investigations of Oehme et al. to try to realize asymmetric hydrogenations using achiral catalysts, relying only on the enantiodifferentiating ac- tion of chiral amphiphiles, led to very small effects [3]. The seven-membered rhodium(I) chelate of butane-1,4- diyl-bis(diphenylphosphines), [Rh(BDPP)(COD)]BF 4 , gave reliable but unsatisfactory enantioselectivities of up to 8%ee when amphiphiles derived from enantiopure carbohydrates or amino acids were applied. In contrast the rhodium complex of propane-1,3-diyl-bis(diphenyl- phosphine), forming a six-membered chelate ring, proved to be unsuccessful in this respect. The background for the preparation of unsymmetric ligands with two coordinatively distinguishable phos- phorus atoms, which are here presented, was to attempt to enable its rhodium complexes to a higher stereodif- ferentiation in the chiral environment formed by mi- celles of alkyl polyglucosides. Considering the strong electronic effects of P -aryl substituents on the enan- tioselectivity of carbohydrate bisphosphinite catalysts found by RajanBabu et al. [4] we supposed that it might be important to differentiate the electronic state of both phosphorus atoms in the newly synthesized ligands to enable the chiral medium to take effect. Seven-membered chelates were chosen because we had already shown that the enantioselectivity of such rhodium(I) chelates, caused by their high conformative flexibility, is strongly susceptible to the influences of solvents, substrates or additives [2,5]. In special cases this covers nearly the whole range of enantioselectivity from about 90%ee (S ) to nearly 90%ee (R ) for one and * Corresponding author. Tel.: +49-381-4669335; fax: +49-381- 4669324. E-mail address: ruediger.selke@ifok.um-rostock.de (R. Selke). 0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0022-328X(00)00845-7