Synthesis, crystal structure and solution properties of a diastereomeric (p-cymene)ruthenium(II) chiral Schiff base complex

The reaction of [Ru(eta(6)-p-cymene)Cl-2](2) with the chiral Schiff base (S)-(alpha-methylbenzyl)-3,5-di-t-butylsalicylaldimine (HL*) in the presence of NEt3 in CH2Cl2, forms a diastereomeric mixture of (R-Ru, S-C)- and (S-Ru , S-C)-[Ru(eta(6)-p-cymene)(L*)Cl] (1a, 1b). The crystal structure of the complex shows the presence of both the diastereomers in 1:1 ratio in the triclinic space group P1. Both the structures exhibit the presence of a non-covalent CH-pi interaction involving two p-cymene ring protons and the phenyl group attached to the chiral carbon. The H-1 NMR spectra of the complex in CDCl3 display the presence of two diastereomers in a 88:12 ratio at room temperature. The absolute configuration of the major diastereomer in solution has been determined by 2D NOE measurements. Observation of NOE cross peaks involving the C*-H and the p-cymene ring protons indicates a (R-Ru - S-C)configuration of the major diastereomer in solution. (C) 2002 Elsevier Science Ltd. All rights reserved.