FORMATION AND DISSOCIATION KINETICS OF MONOAZIDOBIS(PENTANE-2,4-DIONATO)CHROMIUM(III) AND DIAZIDOBIS(PENTANE-2,4-DIONATO)CHROMIUM(III) - ANEXAMPLE OF UNUSUALLY STRONG CATALYSIS

Reactions of [Cr(pd)(2)(H2O)(2)](+) (1; Hpd is pentane-2,4-dione) with excess NaN3 in the pH range 3.6-4.8 follow the sequence of reaction : 1 --> [Cr(pd)(2)(N-3)(H2O)]2 reversible arrow [Cr(pd)(2)(N-3)(2)](-) 3. The rate constants as a function of reaction parameters led to a de tailed reaction scheme and provided the equilibrium constant for the r eaction 2 reversible arrow 3, in close agreement with the spectrophoto metric value (25.7 melt dm(-3) at 50.0 degrees, I = 1.0 mol dm(-3)). I t has been observed that the kinetic lability of 1 and 2 are comparabl e, that the acid-catalysed aquation of 3 is unusually efficient and th at the rate of azide anation is substantially faster than that for thi ocyanate anation. Plausible implications have been discussed.