Doubly Stereogenic Sandwich Frameworks: Diastereomeric Metallobiscorroles

TL;DR

This paper describes the separation of diastereomers in metallobiscorrole compounds and demonstrates their doubly stereogenic nature for the first time.

Contribution

The first demonstration of doubly stereogenic nature in a sandwich compound through diastereomer separation and characterization.

Findings

Diastereomers of Group 6 metallobiscorrole compounds were separated using thin-layer chromatography.

X-ray structures confirmed the 135° diastereomer, while DFT calculations supported the existence of the 45° diastereomer.

Both diastereomers were fully characterized spectroscopically and shown to be chiral.

Abstract

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.

A number of
Group 6 metallobiscorrole sandwich compounds
with square-antiprismatic coordination were separated into diastereomers
by means of careful preparative thin-layer chromatography.

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