[Athletexxx]

Is the acidic hydrolysis of cis- or trans-[Co(en)2Cl2]+ an associative mechanism (H20 binds and Cl- leaves) or a dissociative mechanism (Cl- leaves and H20 binds)? Can someone please explain to me the difference between associative and dissociative mechanisms too. The book I am using doesn't explain them and I would like to know.

[Flatbutterfly]

Chemistry Ligand substitutions rxns in classical octahedral cmplxs are more complicated than simple association or dissociation.  It is believed the intermediate involves both bond-breaking and bond-making and termed an Interchange mechanism (I).  If there is more bond-making than bond-breaking in the intermediate it is called an Ia mechanism.  On the other hand if there is more bond-breaking than making it is called an Id mechanism.
See, C. E. Housecroft, A. G. Sharpe, Inorganic 4th ed (2012)  p 987.
The earlier pages describe the A and D mechanisms.