Isolation of Enantiomers of a Range of Tris(bidentate)ruthenium(II) Species Using Chromatographic Resolution and Stereoretentive Synthetic Methods

Abstract

A range of chiral building blocks of the type Δ- or Λ-[Ru(pp)²(CO)²]²⁺ {pp = bidentate ligands bpy (2,2'-bipyridine), phen (1,10-phenanthroline) and Me²bpy (4,4'-dimethyl-2,2'-bipyridine)} have been synthesized, and their enantiomeric purity and absolute configurations determined by CD and NMR studies. Decarbonylation using trimethylamine oxide in the presence of the respective pp ligand at room temperature produced the corresponding tris(bidentate) species [Ru(pp)₃]²⁺ with retention of configuration at the ruthenium(II) centre. A general chromatographic technique for resolution of tris-homoleptic complexes of the type [Ru(pp)₃]²⁺ was investigated, with the absolute configurations of the resolved complexes confirmed by CD studies, and the X-ray structural analyses of Δ-(-)-[Ru(Me₂bpy)₃]{(-)-O,O'-dibenzoyl-L-tartrate} and Λ-(+)-[Ru(phen)₃]{(+)-O,O'-di-4-toluoyl-D-tartrate}. Resolution is also reported for the analogous species containing three potential bridging ligands, [Ru(bpm)₃]²⁺ and [Ru(HAT)₃]²⁺ (bpm = 2,2'-bipyrimidine; HAT = 1,4,5,8,9,12-hexaazatriphenylene). The versatility of the chromatographic procedure was demonstrated by the resolution of a series of bis-heteroleptic complexes [Ru(pp)₂(pp')]²⁺ {pp' = dpq (dipyrido[3,2-d:2,3'-f]quinoxaline), dpqc (dipyrido[3,2-a:2,3-d]-6,7,8,9-tetrahydrophenazine), and dppz {dipyrido[3,2-a:2,3'-d]phenazine)}.