The keys of a hash are strings. Any value that you use as the key of a hash is converted to a string. Therefore, if you use a reference as the key to a hash then it loses its "reference-ness" and can no longer be used as a reference.

This is almost certainly a clue that you're trying to do the wrong thing. As GrandFather said, if you step back and explain what you're trying to achieve, we can probably help you achieve it without fighting against Perl.