Most of von Neumann’s mathematics—rings of operators, continuous geometries, matrices of high finite order—was undertaken to find a satisfying philosophy upon which to found quantum theory.
(Boolean algebra over sets is incompatible with Heisenberg uncertainty.)
von Neumann confessed to Ulam that he had failed to find a philosophically satisfying basis for QM.
Gian-Carlo Rota, Husserl and the reform of logic
(reworded by me)