Unique selectivity of rare-earth metal ambiphilic carbenes towards organic molecules and novel reactivity patterns with isonitriles.

Studies on the chemistry of highly active rare-earth (RE) metal ambiphilic carbenes face challenges due to the lack of appropriate model molecular platforms because the corresponding ambiphilic carbenes have empty p-orbitals. Here, the synthesis of novel multi-chelated amidate rare-earth metal pincer complexes bearing ambiphilic carbenes is realized by using indol-2-yl-based ligands. The ambiphilic carbene (indol-2-yl carbon) of these complexes is extremely active and shows unique selective reactivity towards various organic molecules including carbodiimides, imine, diphenyldiazomethane, aluminum alkyls, 9-BBN and isonitriles, which demonstrate a range of unprecedented reactivity patterns such as formal [2 + 2] cyclometallation, [3 + 3] annulation, and aza-[4 + 1] annulation, while unprecedented aza-[4 + 1 + 1] annulation products were isolated from the reactions of the rare-earth metal complexes bearing electrophilic carbenes and strongly polarized metallacyclopropanes with 2,6-dimethylphenylisonitrile. Such reactivities differ sharply from those of common transition-metal complexes with the corresponding substrates. The electronic and steric effects of the ligands and the effects of central metal ions on the reactivity patterns were investigated both computationally and experimentally.