Model Studies of the Interaction of Vanadium(III) and Oxovanadium(IV/V) with the Carbonyl Amide Oxygen

Abstract

A series of vanadium(III) and oxovanadium(IV/V) compounds with the ligands, N-(2-nitrophenyl)pyridine-2-carboxamide (Hpycan), N-(phenyl)pyridine-2-carboxamide (Hpheca), and N-(2-pyridyl)acetamide (Hpyra), containing the amide functionality, was prepared and characterized both in solution and in solid state. All vanadium compounds contain a vanadium-amide oxygen bond. Crystal data for [VOCl(2)(OC(2)H(5))(Hpheca)] (4) are monoclinic; P2(1)/a; a = 12.668(5) Å, b = 8.084(3) Å, c = 17.222(6) Å, alpha = 108.148(12) degrees; Z = 4. In addition to the synthesis and crystallographic studies, the optical, infrared, and magnetic properties of these compounds are reported. Electron paramagnetic resonance [of oxovanadium(IV) species] and (1)H, (13)C{(1)H}, and (51)V nuclear magnetic resonance [of oxovanadium(V) compounds] properties are reported as well.

Insulin-Enhancing Vanadium(III) Complexes

“…1 They are not usually considered for therapeutic applications 2,3 because of rapid oxidation to V(IV/V) in aqueous solutions of pH >3. 4,5 Physiologically relevant oxidation states of vanadium are thought traditionally to be V(IV), as vanadyl, and V(V), often as vanadate. 2 There are examples of V(III) in biological systems; however, these are not very common.…”

“…Mononuclear coordination complexes of V(III) are generally six-coordinate, hydrolytically stable, and axially symmetric with an octahedral or pseudo-octahedral geometry . They are not usually considered for therapeutic applications , because of rapid oxidation to V(IV/V) in aqueous solutions of pH >3. , Physiologically relevant oxidation states of vanadium are thought traditionally to be V(IV), as vanadyl, and V(V), often as vanadate . There are examples of V(III) in biological systems; however, these are not very common .…”

Monomeric Compounds Containing thecis-[V(O)(OH)]+ Core

“…Possible intramolecular VO⋅⋅⋅HOV hydrogen bond or intermolecular VO⋅⋅⋅HOV, VO⋅⋅⋅H 2 O or VO⋅⋅⋅OV interactions resulting in this elongation are excluded, because of the long calculated VO⋅⋅⋅H distance (3.297 Å) and the absence of relevant short contacts in the crystal lattice of 1 . Such an elongation of the VO bond has not been found in [V V O 2 (bipy) 2 ] + ( 3 ;11 mean d (VO) ≈1.626 Å) or in the closely related alkoxo compounds [V V O(OC 2 H 5 )Cl 2 (Hpheca)] ( 4 )12 (Hpheca= N ‐(phenyl)pyridine‐2‐carboxamide), VO 1.585 Å, VOR 1.746 Å), both adopt the cis orientation of the O‐V‐O moiety. Both 3 and 4 are compounds of vanadium( V ) whereas 1 is vanadium( IV ).…”

“…The O1‐V‐O2 angle, 106.8(2)°, of the cis‐ [V IV O(OH)] + core is almost identical to that observed for the closely related cis‐ [V V O 2 (bipy) 2 ] + ion (106.5(2)°) and very close to other hexacoordinate mononuclear vanadium( V ) compounds (hmvc) containing the cis ‐[V V O 2 ] + unit (∼105°),9e in which the two VO bonds of the cis ‐[V V O 2 ] center do not differ by more than ∼0.02 Å unless there are different donor atoms in positions trans to the oxo ligands. In hmvc containing the cis ‐[V V O(OR)] 2+ core the (O)‐V‐(OR) angles are ≈103° and the V V O and V V OR bonds are ≈1.60 and 1.74 Å, respectively 9e,9f, 11, 12…”