Hydrolysis of Bis(p-nitrophenyl)phosphate by Tetravalent Metal Complexes with Kläui's Oxygen Tripodal Ligand

The treatment of HfCl 4 with NaL OEf (L OEt ― = [(η 5 -C 5 H 5 )Co{P(O)(OEt) 2 } 3 ] ― ) in nitric add 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 (μ-OH) 2 ][NO 3 ] 4 (2). The treatment of (NH 4 ) 2 [Ce(NO 3 ) 6 ] with 2 equiv of NaL OEf in water afforded (L OEt ) 2 Ce(NO 3 ) 2 (3), whereas that with 1 equiv of NaL OEt in CH 2 CI 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 Ce[η 1 -OPO(OR) 2 ] 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 {μ-O 2 P(OR) 2 }] 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 °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) × 10 ―3 s ―1 .