Here's why:

* Copper (Cu) has two common oxidation states: +1 (cuprous) and +2 (cupric).

* Chlorine (Cl) has an oxidation state of -1.

To balance the charges, copper would need to be in the +3 oxidation state to form CuCl3. However, copper does not readily form compounds in the +3 oxidation state.

The most likely compound you're thinking of is CuCl2, which is copper(II) chloride.