Chelation in Square-Planar Complexes

As with substitution in octahedral complexes, in chelation in square planar complexes the formation of the first bond is usually rate-determining (see (4.101)). 

Compare the ring closure shown in (4.111) with the corresponding process involving only a unidentate ligand in (4.112), rate constants at 25 °C. 

The comparison has to be made between a first-order rate constant for the unimolecular process and a second-order rate constant for the corresponding intermolecular reaction (Sec. 6.1.1). One may arbitrarily decide on a 1 M concentration of reagent NHj, in which 

X and Y may be H2O or halide groups. A number of reactions of Pd(II) appear to fit this scheme.Ring opening and the subsequent slower displacement of single bonded amine are kinetically separable with M = Au(III), and each step proeeeds via a normal nucleophilic attack. 

The interaction of two metal chelates, MAj with NB2, poses interesting mechanistic problems. Depending on the system, nature of chelating molecules A and B etc., complete exchange may occur, 

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