Salary cap issues notwithstanding, that’s not a good trade for either team without more pieces being switched. Clippers get yet another undersized guard/wing player (they need a big wing not another Redick/Crawford-sized one) and lose a big man from their already thin big man rotation. OKC adds a big man to their already crowded front court and loses their only starting calibre point guard.
OKC also says no because Westbrook currently >> Blake Griffin.
Clippers also say no because they already have one ball dominant guard, have no salary cap flexibility to make a workable roster around the trade you proposed.
The only way this is even remotely plausible is if Westbrook says he wants to go to LA, and Griffin says he wants to go to OKC. Even then, OKC would hold out for than just Griffin (and would need more than just Griffin just to make salaries work).