The possibility of superconductivity arising from interactions involving nearest neighbor singlet pairs is discussed. It is shown that the strong coupling effective Hamiltonian for the Hubbard model only admits extended s-wave solutions, and it is argued that those are suppressed by the Hubbard U. Neglecting hopping terms in the effective Hamiltonian involving three sites while keeping nearest neighbor superexchange and/or density interactions introduces spurious d- and p-wave solutions. A related but more fundamental interaction describing covalent bonds between polarizable ions can give rise to extended s-wave superconductivity, and the relationship with the resonating valence bond picture is discussed.