Intrinsically chiral paddlewheel diruthenium complexes†

A family of heteroleptic paddlewheel diruthenium complexes has been designed to obtain a chiral arrangement of the donor atoms of their equatorial ligands around the metal–metal bond axis. In order to do so, the non-symmetric ligands 2-hydroxy-6-methylpyridinate (hmp) and 2-amino-6-methylpyridinate (amp) were employed to obtain the following four axially chiral compounds: cis-[Ru₂Cl(μ-DPhF)₂(μ-hmp)(μ-OAc)] (Ruhmp), cis-[Ru₂Cl(μ-DPhF)₂(μ-amp)(μ-OAc)] (Ruamp), cis-[Ru₂Cl(μ-DAniF)₂(μ-hmp)(μ-OAc)] (Ru′hmp) and cis-[Ru₂Cl(μ-DAniF)₂(μ-amp)(μ-OAc)] (Ru′amp) (DPhF = N,N′-diphenylformamidinate, DAniF = N,N′-bis(p-methoxyphenyl)formamidinate). All the compounds were studied by single crystal X-ray diffraction, confirming that a racemic mixture containing only one of the two possible regioisomers was obtained in all cases. A general nomenclature system for naming the full configuration of intrinsically chiral paddlewheel molecules is proposed using the C/A convention. In addition, electronic spectroscopy and cyclic voltamperometry data demonstrate the electronic tunable nature of this new platform. Overall, these results provide a novel example of robust and tunable chirality, which is of potential interest to be further exploited.