An NMR study of a 13C‐labeled hypervalent (10‐C‐5) [1] pentacoordinate carbon species

Removal of two electrons from 1,8‐bis(4‐methylphenylthio)‐9‐(2, 6‐dimethoxyphenyl‐1‐13C)‐10‐phenylanthracene (2) provides stable dication 1. Isotopic enrichment (85%) of 13C at the labeled site of the aromatic carbon, between the two sulfurs, makes possible the observation of spin‐spin coupling constants between this 13C‐carbon and the directly bonded equatorial ligand carbons. The magnitudes of these coupling constants (two 1JC1′C2′ = 61.9 Hz and one 1JC1′C9 = 56.3 Hz) suggest that this carbon is sp2 hybridized, with the postulated trigonal bipyramidal (TBP) geometry about this carbon center. The 13C NMR chemical shifts for the 10‐C‐5 carbon (δ 109.3) and for other carbons provide strong evidence against alternative structures for this dication. The data are consistent with the 10‐C‐5 species, with apical sulfonium ligands and equatorial carbons of the hypervalent TBP carbon species 1.