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)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 η(1)-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 (1)H NMR spectroscopy as a square pyramidal η(1)-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.