1. Role of the Entering Group
rate is proportional to the nucleophilicity of entering group
element specific
nPt scale is the relative index of nucleophilicity obtained from the reaction
of the standard complex trans-[Pt(py)2Cl2] in methanol, nPt is defined
according to Eqn:
snPt = Log(ky/ks)
No correlation of nPt scale with other properties of the nucleophiles, such
as basicity, redox potentials, or pH.
E.g. strongly basic ligands such as OH- or OMe- do not
react with Pt(II) substrates.
For the reactivity series I- > Br- >
Cl- the most important factor seems to be the polarizability or
"softness" resulting from the existence in low lying excited states.
PR3 > AsR3 > SbR3 >> NR3
-Notable exceptions to this series are NO2-,
SeCN-, which are "biphilic"
"Biphilic" ligands exhibit different reactivities depending on the charge on
thecomplex.
Biphilic Ligands:
Biphilic properties originate from 
-acceptor properties from
non-bondingelectrons
Availability of non-bonding electrons is dependent on ligand environment