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Nucleophilic Reactivity and Oxo/Sulfido Substitution Reactions of MVIO3 Groups (M = Mo, W)

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posted on 2003-11-05, 00:00 authored by David V. Partyka, Richard J. Staples, R. H. Holm
The nucleophilic reactivity of oxo ligands in the groups MVIO3 in the trigonal complexes [(Me3tacn)MO3] (M = Mo (1), W (10)) and [(But3tach)MO3] (M = Mo (5), W (14)) has been investigated. Complexes 1/10 can be alkylated with MeOTf to give [(Me3tacn)MO2(OMe)]1+ (2/11), silylated with Pri3SiOTf to form [(Me3tacn)MO2(OSiPri3)]+ (3/12), and protonated with HOTf to yield [(Me3tacn)MoO2(OH)]+ (4). Similarly, complexes 5/14 can be silylated to [(But3tach)MO2(OSiPri3)]+ (6/15) and protonated to [(But3tach)MO2(OH)]+ (7/16). Products were isolated as triflate salts in yields exceeding 70%. When excess acid was used, the dinuclear μ-oxo species [(But3tach)2M2O5]2+ (8/17) were obtained. X-ray structures are reported for 24, 68, 12, and 1517. All mononuclear complexes have dominant trigonal symmetry with a rhombic distortion owing to a MOR bond (R = Me, SiPri3, H), which is longer than MO oxo interactions; the latter exert a substantial trans influence on MN bond lengths. Oxo ligands in 5/14 undergo replacement with sulfide. Lawesson's reagent effects formation of [(But3tach)MS3] (9/18), 14 with excess B2S3 yields incompletely substituted [(But3tach)WOS2] (20), and 5 with excess B2S3 yields [(But3tach)MoIVO(S4)] (19). The structures of 9, 19, and 20 are reported. Precedents for MVIS3 groups in five- and six-coordinate molecules are limited. This investigation is the first detailed study of the behavior of MVIO3 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. (But3tach = 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane, Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclonane; OTf = triflate).