Five-membered all-C- and hetero-metallacycloallenoids of group 4 metallocenes

By the incorporation of metal atoms highly unsaturated small carbocycles with high ring strain are stabilized. After the synthesis of the five-membered metallacyclocumulenes (1-metallacyclopenta-2,3,4-trienes) and metallacycloalkynes (1-metallacyclopent-3-ynes) of group 4 metallocenes was accomplished the formation of analogous metallacycloallenes (1-metallacyclopenta-2,3-dienes) was predicted. This review covers the successful formation and isolation of these compounds. The synthesis of the all-C and hetero-substituted (N, S) variants is examined as well as their structure.75