Electrochemistry of monomeric molybdenum(V)-oxo complexes in dimethylformamide

Abstract

The electrochemistry of nine monomeric molybdenum(V)-oxo complexes in dimethylformamide has been investigated by cyclic voltammetry and controlled-potential coulometry at a platinum electrode. MoOC13L (L = o-phenanthroline, ol,a'-bipyridyl), MoOClL2 (L = 8-hydroxyquinoline, 8-mercaptoquinoline), and MoOClL (L = disalicylaldehyde ophenylenediimine, N,N'-dimethyl-N,N'-bis(2-mercaptoethyl)ethylenediamine, N,N'-bis(2-mercapto-2-methylpropyl)-ethylenediamine) are facilely reduced by one-electron reductions to Mo(1V) species. (C2H5)4NMoOC12(salicylaldehyde o-hydroxyanil) is reduced in a two-electron step to an Mo(1II) species. None of the complexes are oxidizable in the voltage range used (+OS0 to -2.50 V vs. SCE) to Mo(V1) complexes. Comparison with reduction peaks for molybdenum(V1)-dioxo complexes indicates the Mo(V) monomers are not obtainable by electrochemical reduction of the Mo(V1) complexes, and are, in some cases, thermodynamically unstable to disproportionation into Mo(1V) and Mo(V1). Implications for redox states in molybdenum enzymes are discussed. IntroductionMolybdenum is now well established as a necessary cofactor for a number of redox and there is considerable current interest in the properties and reactions of its complexes as possible models for these During catalysis, Mo(V) has been identified by electron spin resonance (ESR) spectrometry for the molybdenum enzymes xanthine oxidase, aldehyde oxidase, sulfite oxidase, and nitrate redu~tase.',~*~ The ESR signal appears to arise from a monomeric Mo(V) center as a result of electron transfer to or from the ~u b s t r a t e . '~~~~ Clearly, a knowledge of the structures, properties, and reactions of monomeric Mo(V) complexes is of importance for an understanding of these enzymes.The aqueous chemistry of Mo(V) is dominated by ESR

Sulfur K-edge XAS of WVO vs. MoVO bis(dithiolene) complexes: Contributions of relativistic effects to electronic structure and reactivity of tungsten enzymes

“…First, E o W < E o Mo for strictly analogous redox couples, with potential differences decreasing as bond covalency increases [6,[9][10][11][12][13][14]. Second, in Mo/W enzymes and Mo/W isostructural complexes, oxo transfer from substrate to metal (M IV → M VI ) is faster with tungsten [6,9,[15][16].…”

Synthesis and characterization of rectangular tetranuclear cluster complexes of molybdenum(II) by condensation of quadruply bonded dimers

“…, 22, 1091 Mo4Cl8(MeOH)4 + 8C5H5N = 2Mo2C14(C5H5N)4 + 4MeOH ( 6) UV-visible spectroscopy as the quadruply bonded dimer Mo2C14(C5H5N)4.12 Reactions of Mo4Cl8(MeOH)4 with donor ligands could also be limited to simple ligand substitutions (eq 7). When the amount of trialkylphosphine was Mo4Cl8(MeOH)4 + 4L = Mo4C18L4 + 4MeOH (7) limited to 4 equiv of phosphine/equiv of tetramer, there was nearly quantitative conversion to Mo4C18(PR3)4. Similarly, reactions of the methanol tetramer with weakly coordinating nitriles, RCN, at 25 °C also produced tetrameric clusters, Mo4C18(RCN)4.…”

Electronic properties of thiolate compounds of oxomolybdenum(V) and their tungsten and selenium analogs. Effects of oxygen-17, molybdenum-98, and molybdenum-95 isotope substitution upon ESR spectra

“…15 (iii) The substitution of Se for S or of Mo for W also displaces the band to lower energy (see Figure 2) and the trend is in qualitative agreement with Jorgensen's theory of charge-transfer spectra. 16 This approach utilizes optical electronegativities Xopt (14) (15) Lever, A. B. P. "Inorganic Electronic Spectroscopy"; Elsevier: Am- to predict that energy differences of the first allowed band should be given by AEC1 (cm'1) = 30000|Xopl(S) The absence of these intense absorptions in the spin-paired binuclear analogues [M202(XR)6(0Me)]" (Table II)6 suggests that the singly occupied HOMO b2*(dx>, Mo-X(x*)) is the metal-based orbital involved.…”