  We investigate transport through a mononuclear transition-metal complex with
strong tunnel coupling to two electrodes. The ground state of this molecule is
a singlet while the first excited state is a triplet. We show that a modulation
of the tunnel-barrier due to a molecular distortion which couples to the
tunneling induces a Kondo-effect, provided the discrete vibrational energy
compensates the singlet/triplet gap. We discuss the single-phonon and
two-phonon assisted co-tunneling and possible experimental realization of the
theory.
