CHARACTERIZATION OF TRANSITION-STATES IN HLORO(1,4,7-TRIAZACYCLONONANE)COPPER(II)-CATALYZED ACTIVATED PHOSPHATE DIESTER HYDROLYSIS

The reaction mechanism for Cu[9]aneN(3)Cl(2)-catalyzed hydrolysis of e thyl it-nitrophenyl phosphate was probed using kinetic isotope effects and isotope exchange experiments. The solvent deuterium isotope effec t ((D)k = 1.14), combined with the absence of O-18 incorporation into 4-nitrophenol, suggests that hydrolysis proceeds through intramolecula r attack of the metal-coordinated hydroxide at the phosphorus center. The secondary N-15 isotope effect ((15)k = 1.0013 +/- 0.0002) implies that loss of the leaving group occurs at the rate-limiting step with a pproximately 50% bond cleavage in the transition state. This study is one of the first applications of the secondary N-15 isotope effect to simple metal-promoted hydrolysis reactions, and the result is consiste nt with concerted bond formation and cleavage. A mechanism consistent with the isotope studies is presented.