Dangling or tethering the side chain: (η6-(R)-3-phenylbutanol)Ru(II) complexes: Chiral arene ruthenium complexes: Part 5.

The preparation of optically pure ((R)-3-phenylbutanol)Ru(II) complexes is described. Depending on the reaction conditions and the co-ligands, the chiral alcohol side chain may dangle free at the periphery of the η6-co-ordinated arene ligand or be co-ordinated to the metal to result in a η6:η1-chelate ligand system. A key molecule is the dimeric complex [(η6-(R)-3-phenylbutanol)RuCl2]2 (2) with dangling side chains. It is accessible in good yield either by oxidation and COD ligand exchange of the Ru(0) species [(COD)(η6-(R)-3-phenylbutanol)Ru] (1) (COD=1,5-cyclooctadiene) or by complexation and dehydrogenation of (R)-3-cyclohexa-(1,4-dien-1-yl)-butanol (5). 5 is thus accessible in good yield in two steps from a commercially available starting material. Dimer 2 can be split into mononuclear complexes by heating alcohol solutions to afford tethered [(η6:η1-(R)-3-phenylbutanol)RuCl2] (6), or by reaction with an additional ligand L (L=PR3, P(OR)3, pyridine) to furnish [(η6-(R)-3-phenylbutanol)(L)RuCl2] (7a–f). If 7a–d are reacted with silver salts, the side chain is strapped through chloride elimination to form the diastereomeric salts [(η6:η1-(R)-3-phenylbutanol)(L)RuCl]+X− (8X) (X=BF4, PF6). The absolute molecular structures of the complexes have been determined in the solid state. Especially the side chains exhibit interesting conformational features. The CD spectra of 2, 6, and 7a are reported.