Oxygen Atom Transfer, Sulfur Atom Transfer, and Correlated Electron−Nucleophile Transfer Reactions of Oxo- and Thiomolybdenum(IV) Complexes:  Synthesis of Oxothiomolybdenum(VI) and (Hydroxo)oxomolybdenum(V) Species

Abstract

Reaction of Mo IV O(S 2 PR 2 ) 2 with K{HB(Pr i pz) 3 } [HB(Pr i pz) 3 -) hydrotris(isopropylpyrazol-1-yl)borate] in refluxing toluene affords green L*Mo IV O(S 2 PR 2 -S,S′) complexes [L* ) HB(3-Pr i pz) 2 (5-Pr i pz) -) hydrobis(3-isopropylpyrazol-1-yl)(5-isopropylpyrazol-1-yl)borate; R ) Pr i , Ph], which are converted upon reaction with boron sulfide in dichloromethane to the yellow thio analogues L*Mo IV S(S 2 PR 2 -S,S′). Crystals of L*Mo IV O(S 2 PPr i 2 ) are monoclinic, space group P2 1 /n, with a ) 10.024 (2) Å, b ) 20.999(9) Å, c ) 15.368(5) Å, ) 100.57(2)°, V ) 3180(2) Å 3 , and Z ) 4. Crystals of L*Mo IV S(S 2 PPh 2 ) are monoclinic, space group P2 1 , with a ) 10.801(8) Å, b ) 13.100(5) Å, c ) 12.023(9) Å, ) 99.56(10)°, V ) 1678(2) Å 3 , and Z ) 2. The mononuclear, distortedoctahedral complexes are isostructural and are composed of a terminal chalcogenide ligand [ModO ) 1.671(3) Å, ModS ) 2.126(3) Å], a bidentate dithiophosphinate-S,S′ ligand, and a facial, tridentate L* ligand. In both cases the 5-isopropylpyrazole group is bound trans to the ModE group (E ) O, S). Oxygen atom transfer to L*Mo IV S(S 2 PR 2 ) and sulfur atom transfer to L*Mo IV O(S 2 PR 2 ) produce the oxo-thio-Mo(VI) complexes L*Mo VI -OS(S 2 PR 2 -S). NOESY experiments confirm that the 5-isopropylpyrazole group is trans to the ModO group in these chiral complexes. Ferrocenium oxidation of L*Mo IV E(S 2 PR 2 ) yields the corresponding oxo-and thioMo(V) complexes [L*Mo V E(S 2 PR 2 -S,S′)] + , respectively; the [L*Mo V O(S 2 PR 2 -S,S′)] + complexes react with water to produce (hydroxo)oxo-Mo(V) species, L*Mo V O(OH)(S 2 PR 2 -S), while the thio analogues are decomposed by water. The complex L′Mo V OCl 2 [L′ ) HB(3-Pr i pz) 3 -) hydrotris(3-isopropylpyrazol-1-yl)borate] was prepared by reacting L′Mo VI O 2 Cl with PPh 3 in dichloromethane; this complex does not react with sulfiding agents to produce the analogous thio complex. IntroductionThe simple replacement of a terminal oxo ligand by a terminal thio 2 ligand is a reaction plagued by practical limitations; the facile reduction of high-valent metal centers by sulfide and the formation of polynuclear µ-thio complexes usually conspire to prevent clean reactions. Nevertheless, this reaction has played a vital role in the generation of [Mo VI OS] 2+ , [Mo V -OS] + and [Mo V O(SH)] 2+ complexes, some of which are important models for the molybdenum centers formed during turnover of xanthine oxidase and xanthine dehydrogenase. [3][4][5] Most oxo-thio-Mo(VI) complexes have been produced by sulfidation of oxo complexes; examples include the oxothiomolybdates, [Mo VI O 4-n S n ] 2-, 6 the Wieghardt complexes Mo VI -OS(ONR 2 ) 2 , 7 and the organometallic species (η 5 -C 5 Me 5 )Mo VI -OS(CH 2 SiMe 3 ). 8 Generally, however, sulfidation of oxoMo(VI) complexes does not lead to clean replacement of an

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

“…They are also amenable to conversion into a number of enzyme relevant EPR-active Mo(V) species [38,39]. Related hydrobis(3-isopropylpyrazolyl)(5-isopropylpyrazolyl)borate complexes are also accessible [40].…”

Synthesis and characterization of molybdenum oxo complexes of two tripodal ligands: reactivity studies of a functional model for molybdenum oxotransferases

“…Several model systems for oxotransferases have been developed in order to better understand the reactivity of the molybdenum cofactors and the mechanisms of oxygen atom transfer. [18][19][20][21][22][23][24][25] The general mechanism proposed for the oxygen atom transfer includes a transition state where the molybdenum atom and the substrate are bridged by the oxygen atom that is either entering or leaving the coordination sphere of the molybdenum atom. The redox potentials, and thus potential reactivity/catalytic activity as well as substrate specificity of the enzymes (and model systems) are expected to be considerably influenced by the direct coordination environment of the molybdenum atom.…”

Structural and functional models in molybdenum and tungsten bioinorganic chemistry: description of selected model complexes, present scenario and possible future scopes

“…FDH catalyzes the oxidation of formate to CO 2 and a detailed description of the important biological processes that control the different chemical properties of molybdenum and tungsten to tune the reactivity, substrate specificity and metabolic role of FDHs has appeared recently. 56,57 A re-evaluation 68 of the previous X-ray structural analysis 69 of Mo-FDH active site showed that the [70][71][72][73] The usual problem of redox and hydrolysis reactions of Mo IV S units that leads to the formation of polynuclear complexes was avoided by use of sterically demanding tridentate ligands. However, use of nondithiolene ligands does not mimic the MPT ligand present in the active site.…”