P-31 AND W-183 NMR SPECTROSCOPIC EVIDENCE FOR NOVEL PEROXO SPECIES IN THE H3[PW12O40]YH2O/H2O2 SYSTEM - SYNTHESIS AND X-RAY STRUCTURE OF TETRABUTYLAMMONIUM (MU-HYDROGEN PHOSPHATO)BIS(MU-PEROXO)BIS(OXOPEROXOTUNGSTATE)(2-) - A CATALYST OF OLEFIN EPOXIDATION IN A BIPHASE MEDIUM

Both the ''H-3[PW12O40].yH2O'' and the ''H2WO4/H2O2-H2O/H3PO4'' systems show several P-31 and W-183 NMR signals which may be assigned to new phosphatooxoperoxotungstate species, [PW(x)O(y)]omega-, (x = 1-4). Among these complexes, the novel ''PW2'' anion was studied in the crystalline state and in solution. Several salts of the general formula Q2[HPO4{WO(O2)2)2] were obtained by the reaction of tungstic acid, ''H2WO4'', or H-3[PW12O40].YH2O with hydrogen peroxide, orthophosphoric acid, and the appropriate onium salt, QX (Q+ = [(n-C4H9)4N]+; [{(C6H5)3P}2N]+;[{(C18H37)75%+(C16H33)25%}2N(CH3)2]+. The structure of[(n-C4H9)4N]2[HPO4{WO(O2)2}2] (triclinic P1BAR, a - 10.660(3) angstrom, b = 12.662(3) angstrom, c = 17.723(3) angstrom, alpha = 74.92(2)-degrees, beta = 77.57(2)-degrees, gamma = 86.65(2)-degrees, Z - 2) was refined to R = 0.060 and R(w) = 0.065. The polyanion has one nonbridging and one bridging peroxo group on each W center with slightly elongated peroxo bonds (1.53(3) and 1.56(4) angstrom) in the former case. The structural features compare well with those of previously described complexes, [(n-C6H13)4N]3[PM4O24] (M - MO or W). The vibrational (IR and Raman) and P-31 with W-183 NMR spectra suggest that the overall structure is maintained in organic solvents at room temperature. (R)-(+)-Limonene is stoichiometrically epoxidized at this temperature. The two tungsten(VI) compounds [(n-C4H9)4N]2[HPO4{WO(O2)212] and [(n-C4H9)4N]3[PW4O24], are about 30 times more active than [(n-C4H9)4N]3[PMo4O24]. These differences can be related to the observed nu(O-O) frequencies (IR and Raman, both solid-state and solution spectra).