The influence of the boat-to-chair conversion on the demetallation of the nickel(II) complex of an open-chain tetramine containing a piperazine fragment

The nickel(II) complex with an open chain tetramine containing a piperazine fragment (1) displays an unusual
resistance to demetallation in acidic solution and exhibits a lifetime of about five minutes in a solution 0.1 M in
HClO4 and 7.0 M in NaClO4. Sluggishness with respect to the demetallation is ascribed to the occurrence of the
boat-to-chair conformational conversion of the piperazine fragment, which implies the passage through the highly
energetic half-boat transition state. The use of a high concentration of the inert electrolyte induces a ‘salting out’
effect on both thermodynamics (stability of metal complexes is enhanced) and kinetics (resistance to demetallation
is increased).