Doubly Stereogenic Sandwich Compounds: Separation and Characterization of 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 = meso-tris[3,5-bis(trifluoromethyl)phenyl]corrolato} and W[TDOMePC]2 [TDOMePC = meso- 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.