184372-40-5Relevant academic research and scientific papers
Preparation and Protonation Studies of trans-Dioxorhenium(V) Complexes with Imidazoles
Be?langer, Suzanne,Beauchamp, Andre? L.
, p. 7836 - 7844 (1996)
Reacting ReO2I(PPh3)2 with imidazole (ImH) and its methylated derivatives 1-MeIm, 1,2-Me2Im, 2-MeImH, and 4(5)-MeImH yielded salts of the trans-dioxo cation [ReO2L4]+. Pure stable compounds were isolated for X- = I- and L = ImH, 1,2-Me2Im, and 1-MeIm and X- = B(C6H5)4- and L = 1-MeIm, 2-MeImH and 5-MeImH. The νas(O=Re=O) IR bands were observed between 765 and 794 cm-1, whereas the νs Raman band appeared in the 900-925 cm-1 range. The compounds were also characterized by 1H and 13C NMR and UV-vis spectroscopies. Crystal structures were determined for three compounds: [ReO2(2-MeImH)4][B(C6H5) 4]·3CH3-OH, triclinic, P1?, a = 10.696(3) A?, b = 15.128(4) A?, c = 15.497(4) A?, α = 113.57(2)°, β= 97.25(2)°, γ = 95.94(2)°, Z = 2,R = 0.030; [ReO2(1-MeIm)4][B(C6H5) 4]·H2O·0.5CH3OH, monoclinic, P21/n, a = 15.619(2) A?, b = 9.486(2) A?, c = 27.387(4) A?, β= 97.09(1)°, Z = 4, R = 0.057; [ReO2(5-MeImH)4][B(C6H5) 4], orthorhombic, P212121, a = 10.199(2) A?, b = 13.441(5) A?, c = 28.798(10) A?, Z = 4, R = 0.043. The complexes adopt the trans-dioxo geometry, and the octahedra are remarkably regular. Protonation of [ReO2L4]I was studied in methanol and in water. Acid dissociation constants were determined in aqueous solution for the [ReO(OH)L4]2+ (Ka1) and [ReO(OH2)L4]3+ (Ka2) species of 1-MeIm (pKa1 = 2.0, pKa2 = ～-4.0) and 1,2-Me2Im (pKa1 = ～3.8, pKa2 = ～-4.1). Iodide salts of [ReO(OH)L4]2+ were not stable enough to be isolated, but the B(C6H5)4- salt of [ReO(OH)(1,2-Me2Im)4]2+ was obtained in pure form. The crystal structure of [ReO(OH)(1,2-Me2Im)4] (I3)0.5-(ReO4)1.5 (monoclinic, I2/a, a = 23.290(8) A?, b = 10.863(7) A?, c = 25.709(8) A?, β= 94.36(3)°, Z = 8, R = 0.060) showed the presence of octahedral dications in which the oxo and hydroxo groups are trans to one another and the Re-N bonds are displaced to the Re-OH side by the steric effect of the multiple Re-oxo bond. The σ-donor ability of imidazole, greater than that of pyridine, leads to more stable [ReO2L4]+ compounds in which the Re=O double bond character is lower and the oxo groups are better nucleophiles.
