MULTIPLE BONDS BETWEEN TRANSITION-METALS AND MAIN-GROUP ELEMENTS .124. STRUCTURES AND REACTIVITY OF ACYLPERRHENATES

Two structural types of perrhenic anhydrides result from treatment of Re2O7 with carboxylic anhydrides (RCO)2O in acetonitrile or tetrahydro furan solution. Strongly electron-withdrawing groups, cf. R = CF3, thu s lead to complexes of type RC(O)-O-ReO3.2L (L = CH3CN, thf) exhibitin g eta1-coordinated carboxylato groups and octahedral coordination at r henium(VII), both in solution (IR, O-17 NMR) and in the solid state (X -ray crystal structure of CF3C(O)-O-ReO3.2CH3CN (crystal data: space g roup P2(1)/n (No. 14), a = 10.522(3) angstrom, b = 8.193(1) angstrom, c = 13.094(4) angstrom, beta = 90.59(1)degrees, Z = 4)). Analogous coo rdination is observed in the X-ray crystal structure of Re2O7.2CH3CN ( space group P2(1)/m (No. 11), a = 5.363(1) angstrom, b = 11.763(2) ang strom, c = 8.273(2) angstrom, beta = 94.395(9)degrees, Z = 2)). By way of contrast, anhydrides of weak carboxylic acids, cf. R = CH3, yield mixed anhydrides of general formula RC(O)-OReO3.L (L = CH3CN, thf), th e structures of which compounds display octahedral rhenium(VII) and et a2-coordinated carboxylato groups. These structures are again observed in solution and in the solid state (X-ray crystal structure of CH3C(O )-OReO3.CH3CN (space group C2/m (No. 12), a = 14.818(8) angstrom, b = 6.976(2) angstrom, c = 7.390(4) angstrom, beta = 94.64(2)degrees, Z = 4)). As a result of these structural features, only mixed anhydrides c ontaining strongly electron-withdrawing substituents react cleanly wit h alkyltin compounds to yield the alkylrhenium(VII) oxides of the type alkyl-ReO3.