The Quest for Large Group 13 Metallacalixarenes Based on Benzymidazolyl Ligands and Al and Ga Alkyls

Metallacalix[n]arenes derived from AlMe3 or GaMe3 with either 2‐bromo‐1H‐benzimidazole, 2‐Brbzim, or 2‐ethyl‐1H‐benzimidazole, 2‐Etbzim, were obtained by coordination self‐assembly. SCXRD and 1H and 13C NMR in solution are consistent with the isolation of metallacalix[4]arenes 1 and 2, respectively. SCXRD molecular structures of 2‐Etbzim‐based metallacalix[n]arenes show an aluma[6]calixarene complex, 3, and a gallacalix[5]arene, 4. 1H and 13C NMR for 3 and 4 show three species coexisting in solution. The electronic properties of 1–4 along with previously reported [2‐MebzimAlMe2]4 and [2‐MebzimGaMe2]4 were investigated by DFT single point calculations. For the large aluma‐ and gallametallacalix[n]arenes, the analysis of the electrostatic potential show that charge complementarity along with a more flexible cavity than for metallacalix[4]arenes renders self‐encapsulation. Large Group 13 Metallacalix[n]arenes with n=5, 6 derived from AlMe3 or GaMe3 were afforded employing 2‐ethyl‐1H‐benzimidazole (2‐Etbzim), while smaller species with n=4 were obtained using 2‐bromo‐1H‐benzimidazole (2‐Brbzim). Herein, we present synthetic, spectroscopic, and structural studies of these complexes.