CODH, catalytic cycle

Figure 7.2 (a) Active site of O. carboxidovorans CODH. An aqua ligand is weakly bound to the Cu centre but is displaced by CO in the first step of the catalytic cycle, (b) Active site ofi putida 86 QOR. 

Figure 2.29 A catalytic cycle for CODH that avoids formation of a stable thiocar-bonate C-S bonded intermediate in the catalytic cycle (ref. 36). Reproduced by permission of The Royal Society of Chemistry.

Fig. 6 Putative catalytic cycle of CODH involving a Ni - Fe bridging hydride. The bridging hydride is assumed to be stable enough to prevent its fast reaction with a proton. The reaction can be divided into several steps 1) CO2 binds end-on at the axial El site 2) the hydride attacks the bound CO2 forming a transient formate complex 3) the C - OH bond is broken, generating an intermediate that has El occupied by CO and E2 by OH" 4) CO dissociates from Ni as a Ni(II)-bound axial CO is not very stable [135], generating the Credi state that has a bridging hydroxide 5) addition of two electrons via the D- and B-clusters and of two protons via a proton channel leads to dehydration and regeneration of the Cj-ed2 state. The hypothetical Cint form is depicted as having Ni(III). However, an alternative would be a species with Ni(II) and one of the cluster irons oxidized to Fe(III).

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