Ligand Effects on the Oxidative Addition of Halogens to (dpp-nacnac^R)Rh(phdi)

The treatment of (dpp-nacnac^R)­Rh­(phdi) {(dpp-nacnac^R)⁻ = CH­[C­(R)­(N-^<i>i</i>Pr₂C₆H₃)]₂^–; R = CH₃, CF₃; phdi = 9,10-phenanthrenediimine} with X₂ oxidants afforded octahedral rhodium­(III) products in the case of X = Cl and Br. The octahedral complexes exhibit well-behaved cyclic voltammograms in which a two-electron reduction is observed to regenerate the initial rhodium­(I) complex. When treated with I₂, (dpp-nacnac^CH3)­Rh­(phdi) produced a square pyramidal η¹-I₂ complex, which was characterized by NMR and UV–vis spectroscopies, mass spectrometry, and X-ray crystallography. The more electron poor complex (dpp-nacnac^CF3)­Rh­(phdi) reacted with I₂ to give a mixture of two products that were identified by ¹H NMR spectroscopy as a square pyramidal η¹-I₂ complex and an octahedral diiodide complex. Reaction of the square pyramidal (dpp-nacnac^CH3)­Rh­(I₂)­(phdi) with HBF₄ resulted in protonation of the (dpp-nacnac^CH3)⁻ backbone to provide an octahedral rhodium­(III) diiodide species. These reactions highlight the impact that changes in the electron-withdrawing nature of the supporting ligands can have on the reactivity at the metal center.