14 March 2013
Prof. Robert Crabtree (Yale University, New Haven, CT, USA)
Organometallic Precatalysts for Oxidation of Water and Alkyl C-H Bonds
With primary oxidants Ce(IV) and NaIO4, precatalysts of the types Cp*Ir(chel)Cl (chel = dipy, 2-pyridylphenyl and related) mediate oxidation of alkyl C-H to C-OH with retention of configuration at carbon. Calculations by David Balcells and Odile Eisenstein suggest a spin state dependence of the pathway (see Figure).1 For example, cis-decalin is converted to cis-9-decalol. In collaboration with Gary Brudvig, we find that these oxidants, as well as anodic oxidation, lead to water being converted to dioxygen by Cp*Ir(chel)Cl and [Cp*Ir(OH2)3]SO4.2 In some cases the catalysis is homogeneous, in others heterogeneous, a distinction that is made from dynamic light scattering and quartz crystal nanobalance measurements.3 In the case of [Cp*Ir(OH2)3]SO4, for example, a blue layer (BL) of electrochromic iridium oxide is deposited on the anode; this is an extremely active water oxidation catalyst.4
- Zhou, M.; Balcells, D.; Parent, A.; Crabtree, R.H.; Eisenstein, O.: Cp* Iridium Precatalysts for Selective C-H Oxidation via Direct Oxygen Insertion. A Joint Experimental/Computational Study, ACS Catalysis, 2012, 2, 208-218.
- a) Blakemore, J.D.; Schley, N.D.; Balcells, D.; Hull, J.F.; Olack, G.; Incarvito, C.D.; Eisenstein, O.; Brudvig, G.W.; Crabtree, R.H.: Half-Sandwich Iridium Complexes for Homogeneous Water-Oxidation Catalysis, J. Am. Chem. Soc., 2010, 132, 16017–16029; b) Brewster, T.P.; Blakemore, J.D.; Schley, N.D.; Incarvito, C.D.; Hazari, N.; Brudvig, G.W.; Crabtree, R.H.: An Iridium(IV) Species, [Cp*Ir(NHC)Cl]+, Related to a Water-Oxidation Catalyst, Organometallics, 2011, 30, 965-973.
- Schley, N.D.; Blakemore, J.D.; Subbaiyan, N.K.; Incarvito, C.D.; D’Souza, F.; Crabtree, R. H.; Brudvig, G.W.: Distinguishing Homogeneous from Heterogeneous Catalysis in Electrode-Driven Water Oxidation with Molecular Iridium Catalysts, J. Am. Chem. Soc., 2011, 133, 10473-10481.
- Blakemore, J.D.; Schley, N.D.; Olack, G.; Incarvito, C.D.; Brudvig, G.W.; Crabtree, R.H.: Anodic Deposition of a Robust Iridium-Based Water-Oxidation Catalyst from Organometallic Precursors, Chem. Sci., 2011, 2, 94-98.