New arene ruthenium complexes with planar chirality

1,2,4-Trimethyl-cyclohexadiene reacts with RuCl₃ • <i>n</i>H₂O in refluxing ethanol to afford quantitatively [RuCl₂(1,2,4-C₆H₃Me₃)]₂ (<b>1</b>), the coordination of 1,2,4-trimethylbenzene to the ruthenium atom introducing planar chirality at the η⁶-arene ligand. The dinuclear complex <b>1</b> reacts with two equivalents of triphenylphosphine (PPh₃) to give quantitatively, as a racemic mixture of enantiomers, [RuCl₂(1,2,4-C₆H₃Me₃)(PPh₃)] (<b>2</b>), the structure of which has been determined by a single-crystal X-ray structure analysis of (rac)-2. Similarly, 1 reacts with two equivalents of the enantiopure phosphine (1S,2S,5R)-(+)-neomenthyldiphenylphosphine (nmdpp) to afford in good yield [RuCl₂(1,2,4-C6H₃Me₃)(nmdpp)] (<b>3</b>) as a mixture of diastereoisomers, from which the isomer <b>3a</b> was isolated by crystallisation. A single-crystal X-ray structure analysis of <b>3a</b> allowed the determination of the absolute configuration at the planar chiral ^η6-arene moiety. Finally, complex 1 reacts with one equivalent of the diphosphine ligand 1,1′-bis(diphenylphosphino)ferrocene (dppfc) to give the heteronuclear complex [RuCl₂(1,2,4-C₆H₃Me₃) (dppfc)RuCl2(1,2,4-C₆H₃Me₃)] (<b>4</b>). All complexes were fully characterised by elemental analysis, mass spectrometry, NMR and IR spectroscopies.