Which of the following cannot be used as Lewis acid in the electrophilic substitution of benzene?
- $\ce{BF3}$
- $\ce{SbCl3}$
- $\ce{FeCl3}$
- $\ce{PF3}$
My Attempt:
- $\ce{BF3}$ and $\ce{FeCl3}$ are Lewis acids.
- $\ce{PF3}$ though it has a filled s and p orbitals it can accept electrons from donors and expand its coordinate number up to six due to vacant d orbitals. It acts as a mild Lewis acid.
- $\ce{SbCl3}$ has a completely filled s,p,d orbitals so it can no longer accept electrons, hence doesn't act as a Lewis acid.
My answer is option (2) but the answer provided is (4), where am I going wrong?