Cerium(III) and cerium(IV) nitrate complexes of trialkylphosphine oxides

The reactions of ammonium cerium(IV) nitrate, (NH4)2Ce(NO3)6 (CAN) with trialkylphosphine oxides, R3PO (R = Et, iPropyl, nBu3, iBu3PO, tBu3PO, Cy3PO (Cy = cyclohexyl) and Oct3PO (Oct = n-octyl)) have been investigated by 31-P NMR spectroscopy in a variety of conditions. Reactions with acetone solutions of excess of CAN and R3PO and of solid CAN with chloroform solutions of R3PO and aqueous solutions of CAN with chloroform solutions of R3PO led to the observation of Ce(NO3)4(R3PO)2. 31-P NMR spectroscopy and conductimetric titration of acetone solutions of CAN with R3PO confirm the initial reactions is the formation of Ce(NO3)4(R3PO)2 (R = Et, Bu, Cy, Oct) followed by a slower reaction to form the ionic [Ce(NO3)3(R3PO)3][NO3]. The isolation of pure complexes has not proved possible in most cases but crystals suitable for x-ray analysis were extracted in some instances. The structures of the Ce(IV) complexes [Ce(NO3)4(Cy3PO)2] and [Ce(NO3)3(Et3PO)3][NO3] and the related Ce(III) complexes [Ce(NO3)3(Cy3PO)3] and [Ce(NO3)3(H2O)3(Et3PO)] are reported.