Multiple Bonds Between Main Group Elements and Transition Metals. 151. Trioxorhenium(VII) Alkoxide Complexes

The reaction of Me₃SiOReO₃ with trimethylsilyl ethers Me₃SiOR (R = Me, CMe₂CMe₂OMe, CMe₂CMe₂OH, CMe₂CMe₂OSiMe₃) yields the trioxorhenium(VII) alkoxide complexes [ReO₃(OMe)(MeOH)]₂ (1), ReO₃(OCMe₂CMe₂OMe) (2), ReO₃(OCMe₂CMe₂OH) (3), and the glycolate complex (Me₃SiO)ReO₂(OCMe₂CMe₂O) (4), respectively. The alkoxides 1−4 have fluxional structures at room temperature in solution on the ¹⁷O NMR time scale. The trigonal bipyramidal structure of 2, in the crystal, is static in solution only at −90 °C. The protic hydrogen of 3 can be abstracted by lithium 2,2,6,6-tetramethylpiperidinate to give the ionic complex Li[ReO₃(OCMe₂CMe₂O)] (5). [ReO₃(OMe)(MeOH)]₂ (1) crystallizes from dichloromethane in the space group P1̄ with unit cell dimensions a = 6.276(3) Å, b = 6.720(3) Å, c = 8.005(4) Å, α = 109.39(3)°, β = 99.48(3)°, γ = 110.31(2)°, V = 238.3 ų, and Z = 1; the structure was refined to R = 0.050 and R_w = 0.056. ReO₃(OCMe₂CMe₂OMe) (2) crystallizes from toluene in the space group Pbca with unit cell dimensions a = 8.263(2) Å, b = 10.884(3) Å, c = 22.963(5) Å, V = 2065 ų, and Z = 8; the structure was refined to R = 0.044 and R_w = 0.028. ReO₃(OCMe₂CMe₂OH) (3) crystallizes from dichloromethane in the space group C2/c with unit cell dimensions a = 12.327(5) Å, b = 10.973(3) Å, c = 14.491(6) Å, β = 90.22(2)°, V = 1960 ų, and Z = 8; the structure was refined to R = 0.047 and R_w = 0.030. (Me₃SiO)ReO₂(OCMe₂CMe₂O) (4) crystallizes from n-pentane in the space group P2₁/c with unit cell dimensions a = 12.042(8) Å, b = 10.782(2) Å, c = 12.485(9) Å, β = 117.44(3)°, V = 1439 ų, and Z = 4; the structure was refined to R = 0.044 and R_w = 0.044. The edge-sharing bioctahedral complex 1 has bridging methoxy and terminal methanol ligands trans to rhenium−oxygen double bonds. The rhenium centers in compounds 2 and 3 are pentacoordinated and located in a distorted trigonal bipyramidal geometry. The alkoxy function of the alkoxy ligand −OCMe₂CMe₂OR (R = H, Me) is located in the equatorial plane, and the Lewis base (−OMe, −OH) is bonded trans to an oxygen atom in an axial coordination site. (Me₃SiO)ReO₂(OCMe₂CMe₂O) (4) has a similar geometry to 2 and 3 with a trimethylsiloxy ligand trans to an alkoxy function in an axial position.