Acetylenic Carbon-Containing Stable Five-Membered Metallacycles

Abstract

Due to the linear property around an acetylenic carbon, the introduction of such an atom to a small cycle would result in high ring strain. Currently, the smallest isolated rings are five-membered, including metallacycloalkynes and metallapentalynes. Both types contain at least one unusual small bond angle around the acetylenic carbon, thus exhibiting abnormal reactivities. This feature article gives a comprehensive overview on these two kind complexes. The synthesis and reactivities are extensively described, the source of stability is presented, and the future prospect is discussed. The article aims to provide a better development for the chemical diversity of five-membered metallacycloalkynes and metallapentalynes.

1-Zirconacyclobuta-2,3-dienes: synthesis of organometallic analogs of elusive 1,2-cyclobutadiene, unprecedented intramolecular C–H activation, and reactivity studies

“…Organometallic complexes of early transition metals show great potential for a variety of unusual bond activation reactions and for the stabilisation of exotic bond situations. 1 In this context the study of formation and reactivity of unsaturated, unusual five-membered metallacycles such as 1-metallacyclopent-3-ynes, 2 1-metallacyclopenta-2,3,4-trienes 3 or 1-metallacyclopenta-2,3-dienes 4 has attracted great attention in the past. In these molecules, the metal centre plays an important role for the stability of the seemingly abnormal cyclic geometries, interacting with the central double or triple bond of the metallacyle.…”

Take a “Snapshot” of New Syntheses, Reactions, and Characterizations from Unusual Unsaturated Ring Strained Group 4 Metallacycles

“…In the above mentioned recent review by Hu and Li it was again summarized, that the incorporation of a metal center is an elegant method to reduce the ring strain and to stabilize highly strained acetylenic carbon‐containing compounds. [1l] This article…”