1. Homoleptic carbonyl complexes exhibit only one CO band.
The number of carbonyl bands depends on the number of unique carbonyl ligands, which in turn is influenced by geometry and symmetry.
2. What does the Tolman Electronic Parameter measure?
The TEP is the A1 carbonyl stretch in complexes of the type [Ni(CO)3L]. It is therefore directly linked to the amount of backdonation to the carbonyl ligands.
3. Nucleophilic attack of a bound carbonyl occurs at...
Upon donation of the lone pair to the metal, there will be partial positive charge at the carbon atom, which makes it prone to attack by nucleophiles.
4. Carbonyl complexes are favorably formed with low valent metal centers.
Carbonyl ligands are good pi-acceptors. Low valent metal centers provide sufficient electron density for favorable pi-backbonding to bound carbonyl ligands.