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.