The unperturbed oxo-sulfido functional group cis-Mo{sup VI}OS related to that in the xanthine oxidase family of molybdoenzymes: Synthesis, structural characterization, and reactivity aspects
The oxo-sulfido functional group cis-Mo{sup VI}OS 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 [MoO{sub 2}(OSiPh{sub 3}){sub 2}]/L in dichloromethane yields the complexes [Mo{sup VI}O{sub 2}(OSiPh{sub 3}){sub 2}L] (L = phen (1), Me{sub 4}phen (2), 4,4{prime}-Me{sub 2}bpy (3), 5,5{prime}-Me{sub 2}bpy (4), 2 py (5)) (74--96%), which are shown to have a distorted octahedral structure of crystallographically imposed C{sub 2} symmetry (1, 5) with cis oxo and trans silyloxy ligands. The related reaction system [MoO{sub 3}S]{sup 2{minus}}/2Ph{sub 3}SiCl/L in acetonitrile affords the complexes [Mo{sup VI}OS(OSiPh{sub 3}){sub 2}L] (L = phen (6), Me{sub 4}phen (7), 4,4{prime}-Me{sub 2}bpy (8), 5,5{prime}-Me{sub 2}bpy (9)) (36--69%). From the collective results of elemental analysis, mass spectrometry, {sup 1}H NMR, and X-ray structure determinations (6, 7), complexes 6--9 are shown to contain the cis-Mo {sup VI}OS 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{double{underscore}bond}O (1.607(5) (6), 1.645(5) (7) {angstrom}) and Mo{double{underscore}bond}S (2.257(3) (6), 2.203(2) (7) {angstrom}) 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{double{underscore}bond}O 1.71--1.72 {angstrom}; Mo{double{underscore}bond}S 2.18--2.19 {angstrom}) 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 Ph{sub 3}P in dichloromethane results in sulfur abstraction and formation of [Mo {sup V}OCl(OSiPh{sub 3}){sub 2}(Me{sub 4}phen)] (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{double{underscore}bond}O/Mo{double{underscore}bond}S bond strengths. Complexes 6--9 should allow exploration of the biologically significant cis-Mo {sup VI}OS group.
- Research Organization:
- Harvard Univ., Cambridge, MA (US)
- Sponsoring Organization:
- National Science Foundation (NSF); National Institutes of Health (NIH); Swedish Natural Research Council; USDOE
- OSTI ID:
- 20000073
- Journal Information:
- Inorganic Chemistry, Vol. 38, Issue 18; Other Information: PBD: 6 Sep 1999; ISSN 0020-1669
- Country of Publication:
- United States
- Language:
- English
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