Retracing the evolution of monometallic ruthenium-arene catalysts for C-C bond formation

Preformed or in situ generated monometallic ruthenium-arene complexes with the generic formula RuX2(arene)(L) (L = phosphine or N-heterocyclic carbene) are versatile and efficient catalyst precursors for olefin metathesis and atom transfer radical reactions. Their synthesis is usually accomplished using simple and straightforward experimental procedures starting from the [RuCl2(p-cymene)](2) dimer. This article retraces their evolution over the past 20 years and highlights similarities and differences with the parallel development of well-defined RuX2(=CHR)(L-1)(L-2) ruthenium-alkylidene catalysts.