Unusual Ar−H/Rh−H <i>J</i>_HH NMR Coupling in Complexes of Rhodium(III): Experimental Evidence and Theoretical Support for an η¹−Arene Structure

The synthesis and structural properties of three new hydridorhodium(III) complexes are reported. Hydrogenolysis of the cyclometalated rhodium dichloride complexes [RhCl2{(S,S)-benbox(Me2)}] (2a−c) leads to formation of the new complexes [RhCl2(H){(S,S)-ip-benbox(Me2)H}] (3a−c) in 45% to 85% yield. Compounds 3a−c were found to have unusual features by NMR spectroscopy: in particular, downfield shifted aryl proton resonances (8.88−9.03 ppm) that were coupled to the rhodium hydride resonances. Using X-ray crystallographic studies, a variety of solid- and solution-state characterization techniques, and DFT calculations, these features were attributed to the presence of weak π-type η1-arene interactions in 3a−c.