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Ligand Effects on the Oxidative Addition of Halogens to (dpp-nacnacR)Rh(phdi)

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posted on 19.11.2012, 00:00 by David W. Shaffer, Scott A. Ryken, Ryan A. Zarkesh, Alan F. Heyduk
The treatment of (dpp-nacnacR)­Rh­(phdi) {(dpp-nacnacR) = CH­[C­(R)­(N-iPr2C6H3)]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-nacnacCH3)­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-nacnacCF3)­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-nacnacCH3)­Rh­(I2)­(phdi) with HBF4 resulted in protonation of the (dpp-nacnacCH3) 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.