Reactivity of Mo−O_t Terminal Bonds toward Substrates Having Simultaneous Proton- and Electron-Donor Properties:  A Rudimentary Functional Model for Oxotransferase Molybdenum Enzymes

Abstract

In order to study the reactivity pattern of Mo-O t bonds associated with anionic sulfur ligands, precursor complexes MoO 2 L‚D (H 2 L ) S-methyl 3-(2-hydroxyphenyl)methylenedithiocarbazate; D ) CH 3 OH (1), H 2 O (2)) were synthesized. Complex 2 crystallizes in the orthorhombic space group P2 1 2 1 2 1 , with a ) 6.079(1) Å, b ) 11.638-(2) Å, c ) 17.325(2) Å, V ) 1225.7(4) Å 3 , and Z ) 4. In its reaction with PhNHOH, 1 forms a seven-coordinate oxaziridine compound [MoO(η 2 -ONPh)L‚CH 3 OH] (3) by oxo-rearrangement (elimination-substitution) without a change in the molybdenum oxidation state. The crystal data for 3 are a ) 9.573(3) Å, b ) 9.859(2) Å, c ) 10.604(3) Å, R ) 95.90(2)°, β ) 95.81(2)°, γ ) 112.12(2)°, V ) 911.5(4) Å 3 , Z ) 2, and triclinic space group P1 h. In contrast to that of the precursor compound 1 (Mo-O t ) 1.700(4) Å), the terminal Mo-O t distance in 3 (1.668(2) Å) is typical of Mo-O bonds of order 3, which drives the formation of an apparently unstable threemembered metallacycle Via spectator oxo stabilization (Rappe ´, A. K.; Goddard, W. A., III. J. Am. Chem. Soc. 1982, 104, 448). With thioglycolic acid, 1 undergoes an oxo-transfer reaction through a coupled electronproton transfer mechanism involving two steps, each having first-order dependence on H 2 tga concentration. The system offers an interesting reactivity model for the oxo-transfer pathway of oxidoreductase Mo enzymes.+IV Via a short-lived mononuclear EPR-active Mo(V) (S ) 1 / 2 ) intermediate during the turnover. 5a,8,9 This information has prompted several recent reports on oxomolybdenum complexes of biomimetic ligands. 7d,10-25 Numerous reactions that replicate the primary oxygen atom transfer † Indian Association for the Cultivation of Science.

Synthesis, Structure, and Reactivity of a New Mononuclear Molybdenum(VI) Complex Resembling the Active Center of Molybdenum Oxotransferases

“…Even the length of the metalϪoxygen double bond (Moϭ O) axial to the coordinated pyridine ligand, which is known to be highly influenced by axial coordination in many (oxo)metal complexes and is thought to be a measure of σ-donor capacity of the coordinated ligand, remains practically unchanged. [12,14,20,21] The length of the relevant bond [N(3)ϪMo] is found to be longer than the other type of molybdenumϪnitrogen (azomethine) bond N(1)ϪMo, and indicates rather weak attachment of the pyridine ligand to the MoO 2 2ϩ moiety. This is substantiated by TG and DTA studies of 4, which reveal rather easy loss of the pyridine ligand on controlled heating.…”

“…The lengths of the MoϭO, MoϪO and MoϪN bonds are unexceptional. [12,14,20,21] The Mo acceptor center is displaced from the average equatorial plane described by O(1)ϪO (3) fovibrio gigas. [22,23] This displacement, naturally, makes the Mo VI acceptor center somewhat inaccessible to the donor approaching from the opposite direction.…”

cis-Dioxomolybdenum(VI) complexes of sterically encumbered phenol-based tetradentate N2O2 ligands: Structural, spectroscopic, and electrochemical studies

“…Electrospray ionization (ESI) mass spectra were recorded on a QTOF Model YA263 Micro Mass Spectrometer. UV-Vis and IR spectra (as KBr pellet) were obtained as described elsewhere [15,19]. Electrochemical measurements were carried out using a BAS 100 B/W electrochemical workstation.…”

“…For quite some time, we have an ongoing project on the reactivity of Mo-O t bonds of cis-MoO 2 compounds, specially in sulfur-rich coordination environments [15]. Herein, we report the syntheses, structural, and spectroscopic characterization of two cis-MoO 2 compounds in a phenol-based sterically encumbered N 2 O 2 ligand environment.…”

Ab initio and semiempirical computational studies on 1‐{(2E)‐2‐[(aminocarbonothioyl)hydrazono]‐2‐(3‐mesityl‐3‐methylcyclobutyl)ethyl}‐pyrrolidine‐2,5‐dione

“…The biological activity of thiosemicarbazones is related to their chelating ability with transition metal ions, bonding through N, N, and S atoms [3] or O, N and S atoms [4][5][6]. The presence of substituents at the 4-position has been shown to affect the activity of thiosemicarbazones and their metal complexes [7].…”