Mechanism of hydroxo-bridge cleavage in dicobalt(III) complexes

Taylor, R. S.; Sykes, A. G.

doi:10.1021/ic50140a047

Cited by 3 publications

(1 citation statement)

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“…Mononuclear metal-aqua ion chemistry is well-established even for the less oxophilic late transition metals, , and polynuclear oxy-bridged aqua-clusters are also known . Several μ-oxy dimers of d 6 metal centers, that is, those of Co III , − Rh III , − and Ir III , have been reported, but only one Ir IV μ-oxy-dimer has been characterized so far. 17 O NMR is the method of choice to probe the solution chemistry of such aqua- and polyoxo-ions, but has rarely been used to investigate functional water-oxidation catalysts. , The quadrupole-broadened resonances and the large shift range of the 17 O nucleus (>1000 ppm) make it virtually insensitive to paramagnetic effects in solution, providing a convenient probe for metal-oxo compounds across different oxidation states.…”

Section: Resultsmentioning

confidence: 99%

Precursor Transformation during Molecular Oxidation Catalysis with Organometallic Iridium Complexes

et al. 2013

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We present evidence for Cp* being a sacrificial placeholder ligand in the [Cp*Ir(III)(chelate)X] series of homogeneous oxidation catalysts. UV-vis and (1)H NMR profiles as well as MALDI-MS data show a rapid and irreversible loss of the Cp* ligand under reaction conditions, which likely proceeds through an intramolecular inner-sphere oxidation pathway reminiscent of the reductive in situ elimination of diolefin placeholder ligands in hydrogenation catalysis by [(diene)M(I)(L,L')](+) (M = Rh and Ir) precursors. When oxidatively stable chelate ligands are bound to the iridium in addition to the Cp*, the oxidized precursors yield homogeneous solutions with a characteristic blue color that remain active in both water- and CH-oxidation catalysis without further induction period. Electrophoresis suggests the presence of well-defined Ir-cations, and TEM-EDX, XPS, (17)O NMR, and resonance-Raman spectroscopy data are most consistent with the molecular identity of the blue species to be a bis-μ-oxo di-iridium(IV) coordination compound with two waters and one chelate ligand bound to each metal. DFT calculations give insight into the electronic structure of this catalyst resting state, and time-dependent simulations agree with the assignments of the experimental spectroscopic data. [(cod)Ir(I)(chelate)] precursors bearing the same chelate ligands are shown to be equally effective precatalysts for both water- and CH-oxidations using NaIO4 as chemical oxidant.

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