Synthesis and reactivity of oxo-peroxo-vanadium(V) bipyridine compounds.
The vanadium(IV) compound [V(IV)O(OH)((t)Bu(2)bpy)(2)]BF(4) (V(IV)O(OH)) ((t)Bu(2)bpy = 4,4'-di-tert-butylbipyridine) is slowly oxidized by O(2) in ethereal solvents to give the oxo-peroxo compound [V(V)O(O(2))((t)Bu(2)bpy)(2)]BF(4) (V(V)O(O(2))) in excellent yield. This and related compounds were fully characterized by NMR, IR, and optical spectroscopies; mass spectrometry; elemental analyses; and an X-ray crystal structure of the 4,4'-dimethylbipyridine analog, [V(V)O(O(2))(Me(2)bpy)(2)]BF(4). Monitoring the reaction of V(IV)O(OH) with O(2) in THF/acetonitrile mixtures by (1)H NMR and optical spectroscopies surprisingly shows that the initial product is the cis-dioxo compound [V(V)(O)(2)((t)Bu(2)bpy)(2)]BF(4) (V(V)O(2)), which then converts to V(V)O(O(2)). Reaction of V(IV)O(OH) with (18)O(2) gives ca. 60% triply (18)O labeled V(V)O(O(2)). The mechanism of formation of V(V)O(O(2)) is complex and may occur via initial reduction of O(2) at vanadium(IV) to give a superoxo-vanadium(V) intermediate, autoxidation of the THF solvent, or both. That V(V)O(2) is generated first appears to be due to the ability of V(IV)O(OH) to act as a hydrogen atom donor. For instance, V(IV)O(OH) reacts with V(V)O(O(2)) to give V(V)O(2). V(V)O(O(2)) is also slowly reduced to V(IV)O(OH) by the organic hydrogen atom donors hydroquinone and TEMPOH (2,2,6,6-tetramethylpiperidin-1-ol) as well as by triphenylphosphine. Notably, the peroxo complex V(V)O(O(2)) is much less reactive with these substrates than the analogous dioxo compound V(V)O(2).
Waidmann
Christopher R
CR
Department of Chemistry, Campus Box 351700, University of Washington, Seattle, Washington 98195-1700, USA.
DiPasquale
Antonio G
AG
Mayer
James M
JM
D015082:2,2'-Dipyridyl / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D008024:Ligands; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D013057:Spectrum Analysis; D014639:Vanadium / Q000737:chemistry*
D008024:Ligands; D009942:Organometallic Compounds; D009943:Organophosphorus Compounds; D014639:Vanadium; C061896:triphenylphosphine; D015082:2,2'-Dipyridyl; D006859:Hydrogen; D010100:Oxygen