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

Abstract

The reaction of [Ru(η⁶-p-cymene)Cl₂]₂ with the chiral Schiff base (S)-(α-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(η⁶-p-cymene)(L)Cl] (1a, 1b). The crystal structure of the complex shows the presence of both the diastereomers in a 1:1 ratio in the triclinic space group P1. Both the structures exhibit the presence of a non-covalent CH-∏ interaction involving two p-cymene ring protons and the phenyl group attached to the chiral carbon. The ¹H 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.