Anhydrous Metal Triflate Complexes

The metal aqua triflate complexes are prepared as previously reported. It was found that drying the solids by rotary evaporation is not sufficient to remove aU of the water therefore the samples should be heated for at least 12h at 90°C under vacuum. Prolonged heating should be avoided, as decomposition of the sample occurs. Extended X-ray absorption fine structure (EXAFS) and vibrational spectral data of anhydrous metal triliates have already been reported and can be used to verify the identity of the products. The colors of the anhydrous metal triflate complexes are white for Mn, white/off-white for Fe, pink for Co, and yellow for Ni. 

---

Among the J ,J -DBFOX/Ph-transition(II) metal complex catalysts examined in nitrone cydoadditions, the anhydrous J ,J -DBFOX/Ph complex catalyst prepared from Ni(C104)2 or Fe(C104)2 provided equally excellent results. For example, in the presence of 10 mol% of the anhydrous nickel(II) complex catalyst R,R-DBFOX/Ph-Ni(C104)2, which was prepared in-situ from J ,J -DBFOX/Ph ligand, NiBr2, and 2 equimolar amounts of AgC104 in dichloromethane, the reaction of 3-crotonoyl-2-oxazolidinone with N-benzylidenemethylamine N-oxide at room temperature produced the 3,4-trans-isoxazolidine (63% yield) in near perfect endo selectivity (endo/exo=99 l) and enantioselectivity in favor for the 3S,4J ,5S enantiomer (>99% ee for the endo isomer. Scheme 7.21). The copper(II) perchlorate complex showed no catalytic activity, however, whereas the ytterbium(III) triflate complex led to the formation of racemic cycloadducts. 

Triflates. The synthesis of U02(03SCF3)2(H20) was first reported in 1994, " and involved the treatment of UO3 with triflic acid in water. The molecular structure of the complex U02(03SCF3)2(H20)3 2(15-crown-5) was subsequently reported, " as was the solution spectrum of U02(03SCF3)2(MeCN)3. The metal coordination environment in both complexes are best regarded as pentagonal bipyramidal uranyl units. Anhydrous and solvent free uranyl tiiflate has since been prepared by several routes, but most conveniently by reaction of UO3 with neat tiiflic add or tiiflic anhydride at elevated temperatures. As discussed above, recrystallization of U02(0Tf)2 from pyridine generates the base adduct U02(0Tf)2(py)3. 

---