Lithium Hexaphenylrhodate(III) and -Iridate(III): Structure in the Solid State and in Solution

Anionic homoleptic organo-transition metal complexes can be prepared from organolithium reagents and transition metal salts and are key reactive intermediates in C-C bond formation. However, the interaction between the anionic component and cationic counterparts of multianionic homoleptic organo-transition metal complexes in solution remains unclear, unlike well-studied monoanionic complexes such as organo-cuprates. Here we have prepared and structurally characterized Contacted\simulated lithium hexaphenylrhodate(III) and -iridate(III) complexes, [Li-(12-crown-4)(2)][MPh6{Li(thf)}(2)] (M = Rh and Ir), as the first examples of hexaaryl complexes of d(6) metals. In the crystals, two Li cations contact the trianionic MPh6 moiety, while the other exists as a solvent-separated ion pair. In THF, hexaphenylrhodate decomposed within 1 h. In contrast, the Ir analog was stable. Li-7 NMR and X-ray absorption fine structure analysis revealed the solution-phase structure of hexaphenyliridate, which maintained a partially contacted ion pair structure even in THF, a coordinating solvent.