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 VIO2(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 VIO2(NN')2 complex as well as kinetic data]. The rate-limiting step in the forward-OAT from [Mo VIO2] to PMe3 is the attack of PMe3 at an oxo ligand with DeltaG not equal (298 K)=64.6 kJ mol(-1). Dissociation of the product OPMe3 is facile with DeltaG( not equal) (298 K)=26.3 kJ mol(-1) giving a mono-oxo [Mo IVO] complex which fills its coordination sphere with a further PMe3 substrate with DeltaG 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 VIO(2)] and [Mo IVO] to dinuclear oxo-bridged [O=MoV-O-MoV=O] species has been calculated as the thermodynamic sink in this system and the back-OAT from dmso to mono-oxo [Mo IVO] to give [Mo VIO2] has been shown to involve an equilibrium between stereoisomeric [Mo VIO2] complexes with an activation barrier of DeltaG not equal (298 K)=113.1 kJ mol(-1).