Besides Cyclic Alkyl Amino Carbenes, another emerging family within the group of carbenes are so called abnormal or mesoionic carbenes. One of the most prominent examples for these mesoionic carbenes are 1,2,3-triazole derived 1,2,3-triazolylidenes. In peculiar, these are interesting because of their high σ-donor strength as well because of their modular synthesis based on the copper catalyzed [3+2] cycloadditon reaction between azides and alkynes. Within the last years, metal complexes of late transition metals have already been shown to be prominent catalysts in various transformations, e.g. proton reduction or the catalytic oxygenation of unactivated C-G bonds.
However, despite the recent interest in these carbenes, metal complexes of early transition metals and the lanthanides haven't been investigated until now.