Harnessing strained ring metal carbenes in transition-metal catalysis

Metal carbenes are versatile motifs that serve not only as catalysts but also as key intermediates in modern organic synthesis. Although considerable attention has been devoted to metal carbenes in non-strained systems, strained metal carbenes, which integrate high-energy strained ring systems with metal carbenes, exhibit distinct reactivity and selectivity in carbene-involved transformations. This feature article systematically reviews recent advances in this emerging field of strained metal carbene chemistry, which are categorized by carbene precursors, including N-sulfonylhydrazones, [1.1.1]propellane, and strained methylenecyclobutane derivatives. It aims to highlight developments and applications of strained metal carbene species, with a particular emphasis on reaction mechanistic insights, selectivity control, and merits and limitations of each strategy, alongside their potential implications for synthetic and medicinal chemistry. We hope that this review will stimulate further innovation among researchers in strained metal carbene chemistry and beyond.