Multiple bonds between main-group elements and transition metals .164. Alkylrhenium(VI) oxides - Synthesis and characterization

Most alkylrhenium(VII) oxides, e.g. ((cyclo)-C3H5)ReO3 (2) are rather sensitive to temperature and moisture with the prominent exception of methyltrioxorhenium (1). The corresponding alkylrhenium(Vl) oxides of formula [RR'(O)-Re(mu-O)](2) [R = R' = (cyclo)-C3H5 (3), iPr (4); R = CH3, R' = C2H5 (5), R = CH3, R' = iPr (6)] are much more stable in this regard. They can be handled in air at room temperature. They were synthesized from Re,O, and dialkylzinc precursors, fully characterized and are available in much higher yields than their Re-VII congeners. Mixed tetraalkyltetraoxodirhenium(VI) complexes (R not equal R') synthesized from 1 and dialkylzinc compounds form as a mixture of cis/trans isomers. They are oily Liquids at room temperature. The Re=O and Re-Re stretching force constants as a measure of the bond strengths, were determined from IR and Raman data.