Acid-Mediated Migration of Bromide in an Antiaromatic Porphyrinoid: Preparation of Two Regioisomeric Ni(II) Bromonorcorroles

The
regioselective halogenation of porphyrinoids is critical for
their selective functionalization, which enables the fine tuning of
their electronic and optical properties. Here we report the synthesis
of two regioisomeric Ni­(II) bromonorcorroles on the basis of the acid-induced
migration of the bromo substituent. Treatment of Ni­(II) dimesitylnorcorrole
with N-bromosuccinimide (NBS) selectively afforded
Ni­(II) 3-bromonorcorrole, which was further converted into Ni­(II)
2-bromonorcorrole upon treatment with hydrogen bromide. In addition,
the reaction of Ni­(II) dimesitylnorcorrole with an excess amount of
NBS afforded the octabrominated product. The reaction mechanism of
the bromination reaction of Ni­(II) dimesitylnorcorrole was investigated
by theoretical calculations.