Organometallic chemistry currently stands as one of the most dynamically advancing branches of chemistry. Within this domain, olefin metathesis plays a pivotal role, facilitating wide-ranging functionalisation of compounds containing carbon-carbon double bonds. As a result, its application extends to both industrial sectors such as petroleum and plastics, as well as laboratory settings. One of the current challenges of this methodology is to develop catalytic methods for the synthesis of olefins as a single stereoisomer, since the geometry of double bond has great influence on, for example, biological activity of pharmaceutical ingredients or physical properties of polymers. Grubbs' pioneering research on moisture-and oxygen resistant, well-defined ruthenium complexes (e.g. Gru-I, Figure ) enabled the widespread use of olefin metathesis in the academy. In subsequent years, ruthenium catalysts underwent a series of diverse modifications. Substitution of one of the phosphines with an N-heterocyclic carbene (NHC) ligand yielded a noticeable enhancement in activity (Gru-II, Figure ), while the replacement of ordinary styrene with isopropoxystyrene increased the stability of the catalyst (Hov-II, Figure ). In 2011, Grubbs developed the first Z-selective ruthenium catalysts bearing an adamantyl group (Ru1, Ru2, Figure ). Further contributions were made by Jensen (Ru3, Figure ), who developed complexes with 2,4,6-triphenylbenzenethiolate ligand, as well as by Schrock and Hoveyda introducing a series of molybdenum complexes (e.g. Mo1, Figure ), yielding catalysts that allowed the efficient synthesis of valuable olefins with high Z-stereoisomer content.