s. The main challenge for the preparation of thiocarbonyl complexes arises from the non-availability of
carbon monosulfide. Thus, the CS ligand is often extruded from thiocarbonyl-containing precursors. One example involves
thiophosgene, which reacts with
disodium tetracarbonylferrate: :Na2Fe(CO)4 + CSCl2 → Fe(CO)4CS + 2 NaCl Instead of thiophosgene, chlorothioformates (ClC(S)OAr) have also been used as a source of CS ligand. The thiocarbonyl analogue of
Vaska's complex is prepared in this way.
Carbon disulfide is another source of thiocarbonyl ligands, although CS2 is less electrophilic than thiophosgene and its alkoxy derivative. Carbon disulfide forms η2-CS2 complexes, which are susceptible to desulfurization. This pattern is illustrated by the reaction of
Wilkinson's catalyst (): : : The reaction of with carbon disulfide gives ca 30% yield of , a trimetallic cluster with a triply bridging thiocarbonyl ligands. Many other thiocarbonyl complexes arise from similarly complicated reactions in modest yield. A variety of other routes have been developed, including addition of sulfur reagents to
metal carbyne complexes. ==Structure and bonding==