The Unperturbed Oxo−Sulfido Functional Group cis-Mo^VIOS Related to That in the Xanthine Oxidase Family of Molybdoenzymes:  Synthesis, Structural Characterization, and Reactivity Aspects

Abstract

The oxo-sulfido functional group cis-MoVIOS is essential to the activity of the xanthine oxidase family of enzymes but has proven elusive to synthesis in molecules containing no other four-electron ligands. A direct route to molecules containing this group has been achieved. The reaction system [MoO2(OSiPh3)2]/L in dichloromethane yields the complexes [MoVIO2(OSiPh3)2L] (L = phen (1), Me4phen (2), 4,4‘-Me2bpy (3), 5,5‘-Me2bpy (4), 2 py (5)) (74−96%), which are shown to have a distorted octahedral structure of crystallographically imposed C 2 symmetry (1, 5) with cis oxo and trans silyloxy ligands. The related reaction system [MoO3S]2-/2Ph3SiCl/L in acetonitrile affords the complexes [MoVIOS(OSiPh3)2L] (L = phen (6), Me4phen (7), 4,4‘-Me2bpy (8), 5,5‘-Me2bpy (9)) (36−69%). From the collective results of elemental analysis, mass spectrometry, 1H NMR, and X-ray structure determinations (6, 7), complexes 6−9 are shown to contain the cis-MoVIOS group in molecules with the same overall stereochemistry as dioxo complexes 1−5. The crystal structures of 6 and 7 exhibit O/S disorder, which was modeled in refinements with 50% site occupancies. The MoO (1.607(5) (6), 1.645(5) (7) Å) and MoS (2.257(3) (6), 2.203(2) (7) Å) bond distances obtained in this way are somewhat shorter and longer, respectively, than expected. Distances obtained by molybdenum EXAFS analysis using the GNXAS protocol for 6−9 (MoO 1.71−1.72 Å; MoS 2.18−2.19 Å) are considered more satisfactory and are in good agreement with EXAFS values for xanthine oxidase. Molybdenum K-edge data for 1 and 6−9 are reported. Reaction of 7 with Ph3P in dichloromethane results in sulfur abstraction and formation of [MoVOCl(OSiPh3)2(Me4phen)] (10), which has a distorted octahedral structure with cis O/Cl and cis silyloxy ligands. Sulfur rather than oxygen abstraction is favored by relative MoO/MoS bond strengths. Complexes 6−9 should allow exploration of the biologically significant cis-MoVIOS group.

A one-pot synthesis of disiloxy, dihalo and dithiocyanato dioxo complexes bearing a bidentate N-ligand from sodium or potassium molybdate tungstate and perrhenate

“…The bond lengths and angles of the MoO 2 (4,4 0 -tBu-2,2 0 -bipy)(OSiPh 3 ) 2 moiety do not vary significantly and are comparable to those found in other molybdenum compounds with the same units and geometry [21].…”

“…When a methyl group in Me 3 SiCl is replaced by a bulkier group such as tert-butyl or when triphenylchlorosilane is used, the reaction with a metaloxo yields stable siloxy compounds. For example, Ag 2 MoO 4 [7], (g 5 -C 5 Me 5 ) WO 3 [7] bis(diethyldithiocarbamate)MoO 2 [4,8], AgVO 3 [7], Ag 2 MoO 4 [8], bis(dithiolene) 2 WO [5].…”

“…In most cases, however, obtaining a metal-oxo species bearing a chloro or a siloxy group as well as a ligand necessitates at least two separate steps, either the metal-oxo bearing a ligand is synthesized and then treated with the chlorosilane [1][2][3][4][5][6] or the chloro or siloxy compound separately prepared is then complexed with the desired ligand [8].…”

Facets of early transition metal–sulfur chemistry: Metal–sulfur ligand redox, induced internal electron transfer, and the reactions of metal–sulfur complexes with alkynes

“…Eq. (2)), shown between (16) and Other monomeric, octahedral oxosulfido-Mo(VI) complexes include MoOS(OSiPh 3 ) 2 L (L = 1,10-phenanthroline or 2,2 0 -bipyridine derivative), prepared by Holm and coworkers [54].…”

Active transition metal oxo and hydroxo moieties in nature's redox, enzymes and their synthetic models: Structure and reactivity relationships

“…Transfer of the sulfur atom rather than the oxygen atom was interpreted in terms of the Mo VI S bond energies being lower than those of the Mo VI O group (Fig. 17) [114]. The tungsten analogues of Mo VI (O) 2 (S)L and Mo VI (O)(S) 2 L, which are the most accurate models of the xanthine oxidases produced to date, have also recently been isolated by Holm and coworkers (Fig.…”