  A new concept is proposed for the paramagnetic metal insulator transition in
the layer perovskite Ca_{2-x}Sr_xRuO_4. Whereas the pure Sr compound is
metallic up to very large Coulomb energies due to strong orbital fluctuations,
structural changes induced by doping with Ca give rise to a interorbital charge
transfer which makes the material extremely sensitive to local correlations.
Using dynamical mean field theory based on finite temperature multi-band exact
diagonalization it is shown that the combination of crystal field splitting and
onsite Coulomb interactions leads to complete filling of the d_xy band and to a
Mott transition in the half-filled d_xz,yz bands.
