Experimental and theoretical study of a truly functional biomimetic molybdenum oxotransferase analogue system

Density functional theory (DFT) computations at the B3LYP/Lanl2DZ level were used to elucidate the oxygen atom transfer (OAT) and coupled electron proton transfer (CEPT) reaction steps involved in the biomimetic catalytic cycle performed by polymer-supported Mo(VI)O(2)(NN')(2) complexes [NN' = phenyl-(pyrrolato-2-ylmethylene)-amine] with water as oxygen source, trimethyl-phosphane as oxygen acceptor and one-electron oxidising agents. The DFT method employed has been validated against experimental data [X-ray crystal structures of a NN' ligand and a Mo(VI)O(2)(NN')(2) Complex as well as kinetic data]. The rate-limiting step in the forward-OAT from [Mo(VI)O(2)] to PMe(3) is the attack of PMe(3) at an oxo ligand with Delta G(not equal) (298 K) = 64.6 kJ mol(-1). Dissociation of the product OPMe(3) is facile with Delta G(not equal) (298 K) = 26.3 kJ mol(-1) giving a mono-oxo [Mo(IV)O] complex which fills its coordination sphere with a further PMe(3) substrate with Delta G(not equal) (298 K) = 39.2 kJ mol(-1). One-electron oxidation to a Mo(V) phosphane complex precedes the coordination of water/hydroxide. Additionally, the comproportionation of [Mo(VI)O(2)] and [Mo(IV)O] to dinuclear oxo-bridged [O=Mo(V)-O-Mo(V)=O] species has been calculated as the thermodynamic sink in this system and the back-OAT from dmso to mono-oxo [Mo(IV)O] to give [MO(VI)O(2)] has been shown to involve an equilibrium between stereoisomeric [MO(VI)O(2)] complexes with an activation barrier of Delta G(not equal) (298 K) = 113.1 kJ mol(-1). (C) 2008 Elsevier Inc. All rights reserved.