SYNTHESIS AND REACTIVITY OF OXOVANADIUM(V) TRIALKOXIDES OF BULKY AND CHIRAL ALCOHOLS

The synthesis and reactivity of a series of stable oxovanadium(V) trialkoxides is reported of alcohols including exo-norborneol, endo-norborneol, 1-adamantanol, 2-adamantanol, (1 R)-endo-(+)-borneol, (IS)-endo-(-)-borneol, and triphenylmethanol. The enantiomerically pure oxovanadium(V) trialkoxides, either all (+) or all (-), are significantly more stable than mixed oxovanadium(V) trialkoxides [(+, +, -) or (-, -, +)]. The reaction between VO(OR)Cl2 and alcohol to form VO(OR)2Cl and HCl was demonstrated to be reversible. The hydrolysis of the oxovanadium(V) trialkoxides was studied in organic solvents using V-51 NMR spectroscopy. In organic solvents a mixture of oxovanadium(V) trialkoxide and H2O is more stable than the corresponding dialkoxide hydroxide and alcohol. It appears that oxovanadium(V) trialkoxides are not inherently unstable as has been suggested by aqueous studies. The redox chemistry of oxovanadium(V) alkoxides was explored, and the derivatives were surprisingly resistant to reduction; reducing reagents such as ascorbic acid and 2-mercaptoethanol were required to reduce the vanadium(V). The unusual stability of these new oxovanadium alkoxides suggests that other derivatives with specific properties can be obtained for structural characterization or use in organic synthesis.