In your example $key stores the reference as string,so you can't convert
in reply to Problem to store referrence as key value in a hash
string back to reference,it will not returns a hard reference.
There is one special kind of hash Tie::RefHash in which we can store reference as keys.
Below is the code i tried,it may help you to store reference as key in a hash.
tie %hash 'tie::RefHash';
%hash =( ["one","two"] => "numbers",
print "@$keyref has $value\n";