Synthesis, Structure, and Reactivity of Magnesium Pentalenides.

The first magnesium pentalenide complexes have been synthesized deprotonative metalation of 1,3,4,6-tetraphenyldihydropentalene () with magnesium alkyls. Both the nature of the metalating agent and the reaction solvent influenced the structure of the resulting complexes, and an equilibrium between and was found to exist and investigated by NMR, XRD, and UV-vis spectroscopic techniques. Studies on the reactivity of with water, methyl iodide, and trimethylsilylchloride revealed that the unit undergoes electrophilic addition at 1,5-positions instead of 1,4-positions known for the unsubstituted pentalenide, , highlighting the electronic influence of the four aryl substituents on the pentalenide core. The ratio of / addition was found to be dependent on the size of the incoming electrophile, with methylation yielding a 60:40 mixture, while silylation yielded exclusively the -isomer.