Labile or Inert Complexes
Labile:
A compound that undergoes reactions with a relatively high rate of substitution.
Inert:
A compound that undergoes reactions with a slow rate of substitution Inert is a relative term, t1/2 > 1 min at 25 oC .
Three main factors that affect the whether a complex is labile or inert:
1. Size: Smaller metal ions tend to be more inert as ligands are held more
tightly.
2. Charge on Metal: The greater the charge on a metal ion in a complex,
the greater the tendency towards the complex being inert.
3. Number of d electrons and configuration.
Octahedral geometry d-electron configuration: labile or inert:
Trans-effect vs Trans-influence:-
Trans-influence:
If “A” forms a very strong sigma-bond to the metal, it competes for the metal orbitals with the leaving group, “X,” thus weakening the M–X bond
Trans-influence determined by sigma-donor strength (basicity):
R3Si – > H – > H3C – , NC – > olefin, CO > R3P > NO2– > I – > Br – > Cl – > H3N > HO –> H2O
Trans-effect:
A strongly sigma-donating and/or pi-accepting group “A” will greatly increase the reaction rate relative to a weak sigma-donor/poor pi-acid “A.” Factors that dominate the trans-effect include: 1. Ground state weakening of M–X bond (trans-influence) 2. Stabilization of the presumed 5-coordinate intermediate
Taking into account BOTH trans-influence and pi- effects:
NO+ > CO > CN – > PR3, H – > H3C – > Ph – > NO2 –, I –> Br – > Cl – > py, H2O, HO –, NH3
Inner Sphere Reactivity:-
Metal Centered:
The gain or loss of ligands
1. Ligand substitution 2. Oxidative addition 3. Reductive elimination 4. Nucleophilic displacement
5. Transmetallation.
Ligand Centered:
Modification of ligands
1. Migratory insertion
a) Carbonyl insertion b) 1,2–insertion 2. Hydride elimination 3. Abstraction.
Labile and Inert Complexes on the basis of CFT:-
