Phosphinsubstituierte Chelatliganden, XXV [1] Diastereoselektive Komplexierung chiraler Phosphinothioformamide mit entferntem Asymmetriezentrum

Abstract

<jats:title>Abstract</jats:title><jats:p> For further studies of the diastereoselective complex formation of ambidentate chiral chelating ligands, we prepared the racemic phosphinothioformamides. Ph<jats:sub>2</jats:sub>P(X )C(S)NHC*HR <jats:sup>1</jats:sup>R<jats:sup>2</jats:sup>, with X = 2e<jats:sup>-</jats:sup> (R<jats:sup>1</jats:sup> = Ph,R<jats:sup>2</jats:sup> = Et: 1a;R<jats:sup>1</jats:sup> = Ph,R<jats:sup>2</jats:sup> = iPr:2a; R<jats:sup>2</jats:sup> = Me,R<jats:sup>2</jats:sup> = Et:3a) and X = O (1b ,2b ) according to a previously reported route. The coordination of 1a -3a to CpM (CO)<jats:sub>3</jats:sub>Cl (M = Mo, W) in m ethanol gives the diastereomeric P.S-chelate complexes, <jats:inline-formula><jats:alternatives><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/Untitled-1.jpg" /></jats:alternatives></jats:inline-formula>(Mo: 4-6, W: 7-9). In solution, epimerisation proceeds to an equilibrium ratio of B/A = 1,5 in case of 4, 5, 7, and 8, but less than 1,1 with 6 and 9. A reduced diastereoselectivity (d.e. 10 -20%) is also observed during the formation of the analogous molybdenum complexes 10a-d with phosphine ligands derived from α-amino acid esters. Ph<jats:sub>2</jats:sub>PC(S)NHC*H(R)COOMe [R = Me (L-Ala), CH<jats:sub>2</jats:sub>Ph (L-Phe). CHMe<jats:sub>2</jats:sub> (L-Val). Ph (D-phenylglycine)]. The results indicate a significant asymmetric induction despite of the four bond distance of the chiral centres.</jats:p>