Vanadyl bis

The vanadium(IV) complex of salen in zeolite was found to be an effective catalyst for the room temperature epoxidation of cyclohexene using t-butyl hydroperoxide as oxidant.88 Well-characterized vanadyl bis-bipyridine complexes encapsulated in Y zeolite were used as oxidation catalysts.101 Ligation of manganese ions in zeolites with 1,4,7-triazacyclononanes gives rise to a binu-clear complex stabilized by the zeolites but allows oxidation with excellent selectivity (Scheme 7.4). 

A series of oxidative transformations with iodylbenzene as the co-oxidant of vanadyl bis(acetylacetonate) have been reported [1116-1118]. In the presence of VO(acac)2, iodylbenzene oxidizes A -steroids into epoxides a radical mechanism was suggested for this reaction. Epoxidation of cholest-5-ene-3-one occurred with high a-selectivity, while the remaining substrates gave mainly p-epoxides. Oxidation of trans-dehydroepiandrosterone acetate (818) afforded epoxide 819 (Scheme 3.323) [1116]. 

Isomerization of Allylic Alcohols and Formation of 1-Halo-1-alkynes. Isomerization of primary and secondary allylic alcohols to tertiary isomers proceeds in CH2CI2 at 25 °C in the presence of a catalyst that is prepared in situ by activation of vanadyl bis(acetylacetonate) or Mo02(acac)2 with (1) (eq 3). On the other hand, terminal alkynes react with (1) in the presence of copper or zinc halides in THF at —15 °C to afford terminal 1-halo-1-alkynes in 40-85% yields. By the same method, 1-cyano-l-alkynes are obtained in 65% yield by use of copper cyanide. 

Related Reagents. Bis(trimethylsilyl) Peroxide-Vanadyl Bis(acetylacetonate). 

A most striking result is the observation of STRAFI echoes for the quadrupolar (I = ) nuclide in the paramagnetic vanadyl bis(acetonato) compound, which has two unpaired electrons on each vanadium atom. This result opens up the prospects of imaging for quadrupolar nuclides in paramagnetic situations in general. 

Catalyst in Oxidation Reactions. DBTO has been used as a catalyst in Fe -mediated oxidation of thiols to disulfides, even though Tri-n-butyl(methoxy)stannane seems to be better suited for this purpose. Epoxidation of terminal alkenes in a two-phase system (chloroform-water) containing H202/ammonium molyb-date/DBTO has also been reported. A combination of DBTO and t-Butyl Hydroperoxide oxidizes allylic alcohols with moderate regio- and stereoselectivity. Tri- and tetrasubstituted double bonds are most easily oxidized and the selectivities are comparable to those of the corresponding Vanadyl Bis(acetylacetonate) mediated reactions. 

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