A molybdenum-dinitrogen complex bearing two ancillary ferrocenyldiphosphine ligands, trans-[Mo(N(2))(2)(depf)(2)] (depf = 1,1'-bis(diethylphosphino)ferrocene), catalyzes the conversion of molecular dinitrogen (N(2)) into silylamine (N(SiMe(3))(3)), which can be readily converted into NH(3) by acid treatment. The conversion has been achieved in the presence of Me(3)SiCl and Na at room temperature with a turnover number (TON) of 226 for the N(SiMe(3))(3) generation for 200 h. This TON is significantly improved relative to those ever reported by Hidai's group for mononuclear molybdenum complexes having monophosphine coligands [J. Am. Chem. Soc.1989, 111, 1939]. Density functional theory (DFT) calculations have been performed to figure out the mechanism of the catalytic N(2) conversion. On the basis of some pieces of experimental information, SiMe(3) radical is assumed to serve as an active species in the catalytic cycle. Calculated results also support that SiMe(3) radical is capable of working as an active species. The formation of five-coordinate intermediates, in which one of the N(2) ligands or one of the Mo-P bonds is dissociated, is essential in an early stage of the N(2) conversion. The SiMe(3) addition to a "hydrazido(2-)" intermediate having the NN(SiMe(3))(2) group will give a "hydrazido(1-)" intermediate having the (Me(3)Si)NN(SiMe(3))(2) group rather than a pair of a nitrido (≡N) intermediate and N(SiMe(3))(3). The N(SiMe(3))(3) generation would not occur at the Mo center but proceed after the (Me(3)Si)NN(SiMe(3))(2) group is released from the Mo center. The flexibility of the Mo-P bond between Mo and depf would play a vital role in the high catalysis of the Mo-Fe complex.
The active oxidant that oxygenates organic substrates is an iron(IV) oxo intermediate, namely, [(tpa)FeIV(O)(CH3CN)]2+ (2), which is formed through OO bond homolysis, according to experimental and computational studies on the reactivity of nonheme iron(III) alkylperoxo complex [(tpa)FeIII(OOtBu)(CH3CN)]2+ (1), which was shown to be a sluggish electrophilic oxidant that is incapable of oxygenating organic substrates. tpa=tris(2‐pyridylmethyl)amine.
Alcohol oxidation by ferrate (FeO(4)(2)(-)) in water is investigated from B3LYP density functional theory calculations in the framework of polarizable continuum model. The oxidizing power of three species, nonprotonated, monoprotonated, and diprotonated ferrates, was evaluated. The LUMO energy levels of nonprotonated and monoprotonated ferrates are greatly reduced by solvent effects, and as a result the oxidizing power of these two species is increased enough to effectively mediate a hydrogen-atom abstraction from the C-H and O-H bonds of methanol. The oxidizing power of these oxidants increases in the order nonprotonated ferrate < monoprotonated ferrate < diprotonated ferrate. The reaction pathway is initiated by C-H bond activation, followed by the formation of a hydroxymethyl radical intermediate or an organometallic intermediate with an Fe-C bond. Kinetic aspects of this reaction are analyzed from calculated energy profiles and experimentally known pK(a) values. The pH dependence of this reaction in water is explained well in terms of a multioxidant scheme.
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