New arene ruthenium complexes with planar chirality

1,2,4-Trimethyl-cyclohexadiene reacts with RuCl3 · nH2O in refluxing ethanol to afford quantitatively [RuCl2(1,2,4-C6H3Me3)]2 (1), the coordination of 1,2,4-trimethylbenzene to the ruthenium atom introducing planar chirality at the η6-arene ligand. The dinuclear complex 1 reacts with two equivalents of triphenylphosphine (PPh3) to give quantitatively, as a racemic mixture of enantiomers, [RuCl2(1,2,4-C6H3Me3)(PPh3)] (2), 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)] (3) as a mixture of diastereoisomers, from which the isomer 3a was isolated by crystallisation. A single-crystal X-ray structure analysis of 3a 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)] (4). All complexes were fully characterised by elemental analysis, mass spectrometry, NMR and IR spectroscopies.