Dinuclear compounds without a metal–metal bond. Dirhodium(III,III) carboxamidates

• Two dirhodium carboxamidates conformational isomers show remarkable thermal stability towards their interconversion.
• The two isomers show negligible differences in their vibrational and electronic absorption spectra.
• The two isomers show substantial differences in their oxidation potentials.
• The dirhodium complexes are stereochemically stable in several oxidation states.

Bis-σ-(phenyl)-tetrakis-μ-(capralactamato)dirhodium(III), formed by oxidative reactions of dirhodium(II) carboxamidates with arylboronic acids promoted by copper(II), exists in two non-interconvertable conformations. In these conformational isomers the caprolactamate ligands are oriented around dirhodium(III) as a propeller with apparent C4 symmetry and in a biplanar array. Cyclic voltammetry and spectroelectrochemistry as well as Raman and resonance Raman spectroscopy of the conformationally distinct Rh26+ carboxamidates have been obtained in order to explore the origin of their non-interconversion. Differences in their vibrational spectra occur only in the low wavenumber spectral region, but there is a 250 mV difference in oxidation potential between conformational isomers consistent with a substantial difference ground state energies. Notably, spectroelectrochemical data show that oxidation does not result in isomerization.

Two thermally stable conformational isomers of a bisphenyldirhodiumcarboxamidate show negligible differences in their vibrational and electronic absorption spectra but substantial differences in their oxidation potentials.Figure optionsDownload as PowerPoint slide