Unconventional Facile Way to Metallanaphthalenes from Metal Indenyl Complexes Predicted by DFT Calculations: Origin of Their Different Thermodynamics and Tuning Their Kinetics by Substituents

Metallaaromatics have attracted considerable
interest from both
experimentalists and theoreticians over the past three decades. However,
most studies in this field have focused on metallabenzene, in which
a CH group is replaced by a transition metal fragment. In comparison
with monocyclic metallabenzenes, bicyclic metallanaphthalenes are
rather limited. Thus, it is urgent to explore more synthetic approaches
to this less developed system. One of the difficulties in the synthesis
of metallanaphthalenes could be due to its low thermodynamic stability
relative to the metal indenyl complexes. Here we present a thorough
theoretical investigation by quantum chemical calculations to explore
the possibility of realizing traditionally “unstable”
metallanaphthalenes by an isomerization of traditionally “stable”
metal indenyl complexes. We systematically investigated how different
substituent(s) at different position(s) on the metallacycle affect
such a rearrangement. Our results indicate that although indenyl complexes
are known to be thermally robust, it should be possible to shift the
thermodynamic and kinetic balance toward the metallanaphthalene complexes
by choosing proper ancillary substituents on the metallabicycle, which
is in sharp contrast to the traditional facile isomerization of metallabenzenes
to cyclopentadienyl (Cp) complexes. Therefore, our findings suggest
a novel avenue to metallanaphthalenes.