PREPARATION OF VARIOUS ONIUM TETRAKIS(OXODIPEROXOMOLYBDO)PHOSPHATES .3. STRUCTURE AND REACTIVITY TOWARDS OLEFINS UNDER BIPHASIC CONDITIONS

Several salts of the general formula O3[PMo4O24] were obtained from th e reaction of molybdic oxide, MoO3, or Na2H[PMo12O40].aq with hydrogen peroxide, orthophosphoric acid and the appropriate onium salt, QX, (Q +=[(n-C6H13)4N]+; [n-C4H9)4N]+; {[(C6H5)3P]2N}+; [o-NH2-C5H5N]+; Arqua d 2HT(R)). The structure of [(n-C6H13)4N]3 [PMo4O24] (monoclinic C2,a= 20.485(3) angstrom; b=15.996(2) angstrom;c= 14.822(3) angstrom;beta=91 .42(1)-degrees;Z=2) was refined with R=0.0465 and R(w)=0.0520. The pol yanion has one bridging and one non-bridging peroxo group on each Mo c entre with relatively short O-O bonds (1.46-1.48 angstrom). The struct ural features compare well with those of the previously described comp lex, [(n-C6H13)4N]3[PW4O24], and with a recently isolated hydrogen-bis (oxodiperoxotungsto)phosphate(2-), [(n-C4H9)4N]2[HPW2O14], but the tun gsten complexes have longer O-O bonds than the molybdenum complex. The vibrational (IR and Raman) and P-31 NMR spectra suggest that the stru cture is conserved in a biphasic medium (CHCl3/H2O2-H2O). 1-Octene and (R)-(+)-limonene are stoichiometrically, or catalytically, in the pre sence of hydrogen peroxide, epoxidized by Q3[PM4O24] (M = Mo or W) and Q2[HPW2O14]. The two anionic tungsten (VI) species are about 30 times more active than the Mo(VI) complex. These differences correlate with the O-O bond distances in the peroxo groups and with the observed nu( O-O) frequencies (IR and Raman, both solid state and solution spectra) .