Hydrolysis of bis(p-nitrophenyl)phosphate by tetravalent metal complexes with Klaui's oxygen tripodal ligand.

The treatment of HfCl(4) with NaL(OEt) (L(OEt)(-) = (eta(5)-C(5)H(5))Co{P(O)(OEt)(2)}(3)) in nitric acid afforded L(OEt)Hf(NO(3))(3) (1). Hydrolysis of 1 in acetone/water (4:1, v/v) yielded the hydroxy-bridged dimer [(L(OEt))(2)Hf(2)(H(2)O)(4)(mu-OH)(2)]NO(3) (2). The treatment of (NH(4))(2)[Ce(NO(3))(6)] with 2 equiv of NaL(OEt) in water afforded (L(OEt))(2)Ce(NO(3))(2) (3), whereas that with 1 equiv of NaL(OEt) in CH(2)Cl(2) gave L(OEt)Ce(NO(3))(3) (4). While 4 is stable in organic solvents such as acetone, it was converted completely to 3 in acetone/water. The treatment of 3 with bis(p-nitrophenyl)phosphate (BNPP) afforded (L(OEt))(2)Ceeta(1)-OPO(OR)(2) (5; R = p-NO(2)C(6)H(4)), whereas the reaction of 4 with NaPO(2)(OR)(2) yielded dinuclear L(OEt)Ce(NO(3))(2){mu-O(2)P(OR)(2)} [R = p-NO(2)C(6)H(4) (6), Ph (7)]. The addition of 3 in acetone to an aqueous solution of NaH(2)PO(4) yielded the cerium(IV) dihydrogen phosphate complex (L(OEt))(2)Ce(PO(4)H(2))(2) (8). Complexes 1-5 and 7 have been characterized by X-ray crystallography. The hydrolysis of BNPP with L(OEt)M(NO(3))(3) (M = Zr, Hf, Ce) in acetone/water has been studied by (1)H NMR spectroscopy. At 25 degrees C, with [Ce] = 20[BNPP], in an acetone-d(6)/N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (4:1, v/v) buffer solution (50 mM) (4:1, v/v), the hydrolysis of BNPP with 4 was found to exhibit first-order kinetics with a rate constant of (1.1 +/- 0.1) x 10(-3) s(-1).