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Updated: Apr 30, 2026

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes
Published on: April 10, 2015
Cationic Sulfonium-Based Tripodal Ligand and Its Rh(I) Complexes
Nitsan Barel1, Shrouq Mujahed1, Kamal Uddin Ansari1
1Institute of Chemistry, Edmond Safra Campus, Hebrew University of Jerusalem, Jerusalem, Israel.
Abstract:
Herein we report the first cationic tripodal ligand-consisting of a sulfonium donor embedded in a tripodal scaffold-together with its mono- and bis-cationic Rh(I) complexes. To elucidate the distinctive properties of this new ligand, its Rh(I) carbonyl complex was subjected to comprehensive structural (XRD) and spectroscopic (NMR, IR) analyses, compared to the isostructural analogs with neutral P-based and anionic Si-based ligands. This comparative study revealed systematic trends along the series, including a progressive shortening of the E-Rh bond (E = Si, P, S) and increasing blue shifts of the CO stretching frequencies. These observations were corroborated by DFT calculations, which also indicated a steady negative charge depletion on Rh along the series. Electrochemical studies (CV) further highlighted the effect of the cationic sulfonium donor, revealing an anodic shift of ∼1.4 V in the Rh(I) reduction potential, relative to the P-based analog. Lewis acidity measurements of the coordinatively unsaturated Rh(I) complexes (by the Guttman-Becket method) yielded acceptor numbers approaching those of polyfluoroaryl boranes for the sulfonium complex. Finally, by representative 2:1 condensations of N-methylindole with carbonyl compounds, we demonstrated how the high Lewis acidity of the Rh(I) center, imparted by its sulfonium coordination, can be exploited in Lewis acid catalysis.
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