As SYS user, it is not possible to create a database link for another user.
If you want to maintain a different schemas database links, and you don't have the literal password of this user, since you usually maintain it's objects directly as SYS, you can use DBMS_SQL to go forward.
This procudure creates links in a different schema:
create or replace procedure repo_link_creator( |
See also: Oraganism: How to Create a Database Link in Another User’s Schema, Creating database links for another schema