Synthesis, characterisation and substitution kinetics of unusually labile trans-[Co(tmen)(diamine)Cl2]+ complexes

The mixed diamine complexes trans-[Co(tmen)(diamine)Cl2]+ have been synthesised (tmen = NH2C(Me)2C(Me)2NH2; diamine = en = NH2(CH2)2NH2, and ibn = NH2C(Me)2CH2NH2). Replacement of one en ligand in trans-[Co(en)2Cl2]+ by one tmen ligand engenders an enormous rate enhancement (2000-fold) for acid hydrolysis. Solvolysis rates have been measured in Me2SO and DMF for these complexes and also trans-[Co(tmen)2Cl2]+ which is more reactive again (104-fold). The measured reactivities in DMF at 2 °C establish that the kinetic effect of replacing each en by tmen is incremental, and the extreme base catalysed racemisation rate for (+)-[Co(tmen)3]3+ can now be explained on this basis.