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

C. Zuccaccia, G. Bellachioma, S. Bolaño, L. Rocchigiani, A. Savini, A. MacChioni

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Abstract

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* –C–CH3 moiety. It was shown that 1 underwent double functionalization of the –C–CH3 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 –C–CH3 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.
Original languageEnglish
Pages (from-to)1462-1468
JournalEuropean Journal of Inorganic Chemistry
Volume2012
Issue number9
Early online date30 Nov 2011
DOIs
Publication statusPublished - 1 Mar 2012

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