Complexes with bulky ligands will prevent the metal from having 18 electrons in outer shell available for bonding

Complexes with bulky ligands significantly influence the electronic configuration and steric accessibility of the central metal atom in coordination chemistry. Bulky ligands, while often stabilizing certain oxidation states or configurations, can impede the coordination of additional ligands necessary for achieving the preferred 18-electron rule.

Explanation of the 18-Electron Rule

1. Concept of the 18-Electron Rule: This rule suggests that many transition metal complexes achieve stability when they have a total of 18 valence electrons. This configuration is reminiscent of the electron configuration of noble gases and is generally associated with a stable electronic state.

2. Role of Bulky Ligands: When bulky ligands such as tert-butyl or cyclopentyl groups are present, they occupy more space around the metal center, making it physically difficult for additional ligands to approach and bind to the metal atom. As a result, the electron count may fall short of 18.

3. Steric Hindrance: This phenomenon illustrates steric hindrance, where the spatial requirements of the bulky ligands prevent the coordination of other ligands that could contribute to reaching the 18-electron count. The more significant the steric hindrance, the more challenging it becomes for the metal complex to surround itself with sufficient atoms to attain stability.

In summary, while complexes with bulky ligands may be stable in their own right, they often do not fulfill the 18-electron stability criterion due to restricted ligand coordination that hinders the addition of electrons necessary for that count. This aspect is crucial in designing metal complexes for specific applications in fields such as catalysis and materials science.