Nucleophilic Reactivity and Oxo/Sulfido Substitution Reactions of M^VIO₃Groups (M = Mo, W)

Abstract

The nucleophilic reactivity of oxo ligands in the groups M(VI)O(3) in the trigonal complexes [(Me(3)tacn)MO(3)] (M = Mo (1), W (10)) and [(Bu(t)(3)tach)MO(3)] (M = Mo (5), W (14)) has been investigated. Complexes 1/10 can be alkylated with MeOTf to give [(Me(3)tacn)MO(2)(OMe)](1+) (2/11), silylated with Pr(i)(3)SiOTf to form [(Me(3)tacn)MO(2)(OSiPr(i)(3))](+) (3/12), and protonated with HOTf to yield [(Me(3)tacn)MoO(2)(OH)](+) (4). Similarly, complexes 5/14 can be silylated to [(Bu(t)(3)tach)MO(2)(OSiPr(i)(3))](+) (6/15) and protonated to [(Bu(t)(3)tach)MO(2)(OH)](+) (7/16). Products were isolated as triflate salts in yields exceeding 70%. When excess acid was used, the dinuclear mu-oxo species [(Bu(t)(3)tach)(2)M(2)O(5)](2+) (8/17) were obtained. X-ray structures are reported for 2-4, 6-8, 12, and 15-17. All mononuclear complexes have dominant trigonal symmetry with a rhombic distortion owing to a M[bond]OR bond (R = Me, SiPr(i)(3), H), which is longer than M[double bond]O oxo interactions; the latter exert a substantial trans influence on M[bond]N bond lengths. Oxo ligands in 5/14 undergo replacement with sulfide. Lawesson's reagent effects formation of [(Bu(t)(3)tach)MS(3)] (9/18), 14 with excess B(2)S(3) yields incompletely substituted [(Bu(t)(3)tach)WOS(2)] (20), and 5 with excess B(2)S(3) yields [(Bu(t)(3)tach)Mo(IV)O(S(4))] (19). The structures of 9, 19, and 20 are reported. Precedents for M(VI)S(3) groups in five- and six-coordinate molecules are limited. This investigation is the first detailed study of the behavior of M(VI)O(3) groups in nucleophilic and oxo/sulfido substitution reactions and should be useful in synthetic approaches to the active sites of the xanthine oxidase enzyme family and of certain tungstoenzymes. (Bu(t)(3)tach = 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane, Me(3)tacn = 1,4,7-trimethyl-1,4,7-triazacyclonane; OTf = triflate).

Specific Incorporation of Chalcogenide Bridge Atoms in Molybdenum/Tungsten-Iron-Sulfur Single Cubane Clusters

“…44 We make several brief observations. (i) Mo-S and W-S distances in the entire set of clusters occur in the range 2.29–2.35 Å, and are substantially longer that the Mo VI -S distance of 2.173(6) Å in 1a , 39 a behavior consistent with reduction to the M III/IV level in reactions 1–3. (ii) N-M-N angles are nearly invariant at 59.5–61.3° and correspond closely to those in other M 0,IV,VI complexes (58–61°) with the same 3 ligand.…”

“…(ii) N-M-N angles are nearly invariant at 59.5–61.3° and correspond closely to those in other M 0,IV,VI complexes (58–61°) with the same 3 ligand. 39,52,53 These angles, dictated by the 6-membered ring of t Bu 3 tach, suggest chelate ring strain larger than that in the less trigonally distorted, generally robust complexes of the type [M III–VI (Me 3 tacn)L 3 ] z in which the ligand is a 9-membered ring with N-M-N angles in the range 73–79° (M = Mo, W). 39,54–57 Ring detachment owing to strain may occur during synthesis but the binding is sufficient to allow serviceable yields.…”

“…39,52,53 These angles, dictated by the 6-membered ring of t Bu 3 tach, suggest chelate ring strain larger than that in the less trigonally distorted, generally robust complexes of the type [M III–VI (Me 3 tacn)L 3 ] z in which the ligand is a 9-membered ring with N-M-N angles in the range 73–79° (M = Mo, W). 39,54–57 Ring detachment owing to strain may occur during synthesis but the binding is sufficient to allow serviceable yields. (iv) Structurally comparable pairs of clusters 4ab , 8ab , 9ab , and 10ab differ only in atom Q and afford the bond length and angle orders Fe-Se > Fe-S and Fe-S-Fe > Fe-Se-Fe for individual and mean values.…”

“…To a suspension of [( t Bu 3 tach)MoS 3 ] 39 (45 mg, 0.10 mmol) in 1 mL of methanol was added a solution of NaSPh (27 mg, 0.20 mmol) in 2 mL of methanol followed by a solution of FeCl 2 (25 mg, 0.20 mmol) in 5 mL of methanol. The reaction mixture was stirred for 12 h. The red-brown solution was evaporated to dryness, the solid was extracted with 5 mL of THF, and the extract was filtered.…”

“…The preceding method on the same scale but with use of [( t Bu 3 tach)WS 3 ] 39 was followed. The product was isolated as a black crystalline solid (28 mg, 30%).…”