An NMR Study of the Oxidative Degradation of Cp*Ir Catalysts for Water Oxidation: Evidence for a Preliminary Attack on the Quaternary Carbon Atom of the -C-CH3 Moiety

作者：Zuccaccia Cristiano; Bellachioma Gianfranco; Bolano Sandra; Rocchigiani Luca; Savini Arianna; Macchioni Alceo^*

来源：European Journal of Inorganic Chemistry, 2012, 2012(9): 1462-1468.

DOI：10.1002/ejic.201100954

• Water oxidation
• NMR spectroscopy
• Hydrogen peroxide
• Iridium
• Cyclopentadienyl ligands

The reaction between H2O2 and two water oxidation catalysts {[Cp*Ir(H2O)3](NO3)2 (1, Cp* = pentamethylcyclopentadienyl) and [Cp*Ir(bzpy)(NO3)] (2, bzpy = 2-benzoylpyridine)} was studied by means of in situ 1D- and 2D-NMR experiments in order to elucidate if catalyst degradation proceeds through the initial functionalization of a quaternary carbon atom (C-attack) or by hydrogen abstraction (H-attack) of the Cp* CCH3 moiety. It was shown that 1 underwent double functionalization of the CCH3 moiety of Cp* leading to the formation of C(OR)CH2OR (R = H or OH) in a strictly analogous manner to that previously observed for the reaction of 1 with Ce4+. On the contrary, two new intermediates associated with the oxidative degradation of 2, which are functionalized only at the quaternary carbon atom(s) of the CCH3 moiety [C(OR)CH3], were intercepted and characterized by NMR spectroscopy. This indicates that the oxidative degradation of water oxidation catalysts, featuring the Cp* ancillary ligand, likely starts with preferential C-attack.

• 出版日期2012-3