Doubly Stereogenic Sandwich Frameworks: Diastereomeric Metallobiscorroles

A number of Group 6 metallobiscorrole sandwich compounds with square-antiprismatic coordination were separated into diastereomers by means of careful preparative thin-layer chromatography. The diastereomers differ with respect to the relative orientation of the corrole macrocycles, which are rotated approximately ± 45° or ± 135° relative to each other. The most clear-cut results were obtained for two tungsten corroles, W[TBCF₃PC]₂ {TBCF₃PC = <i>meso</i>-tris[3,5-bis(trifluoromethyl)phenyl]corrolato} and W[TDOMePC]₂ [TDOMePC = <i>meso</i>-tris(3,5-dimethoxyphenyl)corrolato], for which single-crystal X-ray structures were obtained for the 135° diastereomer; the existence of the 45° diastereomer was inferred by elimination and with support from DFT calculations. For Mo[TBCF₃PC]₂ and W[TBCF₃PC]₂, both diastereomers were also fully characterized spectroscopically and their ¹H NMR spectra were essentially fully assigned. The fact that each diastereomer is chiral and exists as two enantiomers (which was previously demonstrated for the 135° form of a tungsten biscorrole) establishes the doubly stereogenic nature of the metallobiscorrole framework - to our knowledge, the first such demonstration for a sandwich compound.