Kinetics of base hydrolysis of [Co(tetren)dmf]3+ and [Co(tetren)-dmso]3+ (tetren=1,11-diamino-3,6,9-triazaundecane)

The complexes [Co(tetren)dmf](ClO4)3 and [Co(tetren)-dmso](ClO4)3 have been prepared from alpha alpha-[Co(tetren)-Cl](ClO4)Cl (tetren=1,11-diamino-3,6,9-triazaundecane). 1H-n.m.r. and i.r. measurements confirm that the complexes contain O-bonded dmf and dmso. A biphasic reaction is observed in the base hydrolysis of the dmf derivative, monitored by the pH-stat method, with the fast reaction having kOH=1.2*104dm3mol-1s-1 and the slower reaction kOH=1.9*102dm3mol-1s-1 at 25degC and I=0.1moldm3. The fast reaction is assigned to the hydrolysis of the alpha beta(R)-[Co(tetren)dmf]3+ and the slower reaction to that of the alpha The reaction appears to proceed predominantly by a DCB pathway without parallel hydrolysis of coordinated dmf, which has been observed in the hydrolysis of [Co-(NH3)5dmf]3+. Base hydrolysis of [Co(tetren)dmso]3+ was monitored spectrophotometrically over the pH range 4.2 to 5.0. A single reaction was observed with kOH=1.9*106dm3mol-1 s-1 at 25°C and I=0.1 moldm-3. The rapid base hydrolysis is attributed to hydrolysis of the alpha beta(R)- or the alpha beta(S)-[Co(tetren)-dmso]3+ isomer rather than the alpha alpha-isomer.