Synthesis, Structural Characterization, and Multifrequency Electron Paramagnetic Resonance Studies of Mononuclear Thiomolybdenyl Complexes

Abstract

Reaction of Tp*MoVSCl2 with a variety of phenols and thiols in the presence of triethylamine produces mononuclear, thiomolybdenyl complexes Tp*MoVSX2 [Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; X = 2-(ethylthio)phenolate (etp), 2-(n-propyl)phenolate (pp), phenolate; X2 = benzene-1,2-dithiolate (bdt), 4-methylbenzene-1,2-dithiolate (tdt), benzene-1,2-diolate (cat)]. The complexes have been characterized by microanalysis, mass spectrometry, IR, EPR, and UV-visible spectroscopic data, and X-ray crystallography (for the etp, pp, bdt, and cat derivatives). The mononuclear, six-coordinate, distorted-octahedral Mo centers are coordinated by terminal sulfido (MoS = 2.123(1)-2.1368(8) A), tridentate facial Tp*, and monodentate or bidentate O/S-donor ligands. Multifrequency (S-, X-, Q-band) EPR spectra of the complexes and selected molybdenyl analogues were acquired at 130 K and 295 K and yielded a spin Hamiltonian of Cs symmetry or lower, with gzz < gyy < gxx < ge and Az'z' > Ax'x' approximately Ay'y', and a noncoincidence angle in the range of beta = 24-39 degrees . Multifrequency EPR, especially at S-band, was found to be particularly valuable in the unambiguous assignment of the spin Hamiltonian parameters in these low-symmetry complexes. The weaker pi-donor terminal sulfido ligand yields a smaller SOMO-LUMO gap and reduced g-values for the thiomolybdenyl complexes compared with molybdenyl analogues, supporting existing crystallographic and EPR data for an apically coordinated oxo group in the active site of xanthine oxidase.

Spectroscopic and Electronic Structure Studies Probing Covalency Contributions to C–H Bond Activation and Transition-State Stabilization in Xanthine Oxidase

“…51 Furthermore, C s Tp*MoO(bdt) (bdt = benzene-2,3-dithiolate), also displays large rotations (~45°) of the g-tensor relative to A Mo in the mirror plane of this molecule. 52,53 We note that in C s symmetry, one component of the g-tensor and A Mo -tensor are collinear (x-direction). 50 All of our EPR simulations for Inhibited were obtained with Euler rotations (i.e.…”

Spectroscopic Characterization of YedY: The Role of Sulfur Coordination in a Mo(V) Sulfite Oxidase Family Enzyme Form

“…Both Mo(x 2 −y 2 )-S dithiolene and Mo(x 2 −y 2 )-S Cys sulfur covalency contributions are anticipated to increase g 1 . 17 We have shown that deviations from an O oxo -Mo-S thiolate -C dihedral angle of 90° lead to an increase in Mo(x 2 −y 2 )-S v covalency (see Figure 3) in mono-oxo molybdenum thiolate model complexes. 18–20 In contrast, the Mo(x 2 −y 2 )-S σ contribution is anticipated to possess a minimal O oxo -Mo-S Cys -C dihedral angle dependence due to the fact that this is a σ bonding interaction.…”

Scorpionate Complexes as Models for Molybdenum Enzymes

“…The derivatization of [Tp*MoSCl 2 ] has also been reported since 2000 and this has permitted structural and spectroscopic studies of sulfido‐Mo V species, [Tp*MoSX 2 ] {X = phenolate derivative; X 2 = catecholate (cat 2– ), bdt 2– , tdt 2– }, and their comparison to the oxido analogues above , . The sequence of reactions leading to [Tp*MoSX 2 ] is shown in Equation ; it involves sulfidation of 35 to produce [Tp*MoSCl 2 ] 41 followed by metathesis with the triethylammonium salts of X – /X 2 2– to give desired [Tp*MoSX 2 ] 42 .…”