Preparation and reactions of rhenium(VII) trioxo hydrogendiolato complexes and rhenium(VI) oxo bis(diolato) complexes

Abstract

The compound Re₂O₇, Re₂O₇·2H₂O or [ReO₃(OSiMe₃)] reacted with H₂diol to form complexes having the general formula [ReO₃(Hdiol)] where H₂diol = 2,3-dimethylbutane-2,3-diol (H₂pin) or 1,1′-bicyclohexane-1,1′-diol (H₂bicy). In the case of H₂pin the complex [ReO₃(Hpin)]·H₂pin is formed initially in the reaction of rhenium(VII) oxides with an excess of pinacol. The hydrogen bonded free pinacol molecule can be removed by sublimation. The monomethyl derivative of pinacol, HMepin, reacts in a similar way to form the complex [ReO₃(Mepin)]. In the rhenium(VII) compounds the Re atom has a distorted trigonal bipyramidal co-ordination geometry. Pale yellow solutions of [ReO₃(Hdiol)] in CH₂Cl₂ slowly become orange and red crystals having the formula [ReO(diol)₂] may be isolated. The reaction of rhenium(VII) oxides with H₂diol and PPh₃ in the presence of drying agents in CH₂Cl₂ produced the same compounds in high yield. The crystal structures of the rhenium(VI) complexes reveal that the rhenium(VI) cations have square pyramidal co-ordination geometries. The rhenium(VI) oxo bis(diolato) complexes are thermally stable and do not readily undergo oxidation in dry air.