Transition metal thiocarbonyl complex
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A transition metal thiocarbonyl complex is a coordination compound containing the ligand CS. Whereas metal carbonyl complexes are very common, even industrially important, only a few dozen thiocarbonyl complexes are known.[2]
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.[4]
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 (RhCl(PPh3)3):[5]
- RhCl(PPh3)3 + CS2 → RhCl(CS2)(PPh3)3
- RhCl(CS2)(PPh3)3 → RhCl(CS)(PPh3)2 + SPPh3
The reaction of (C5H5)2Ni2(CO)2 with carbon disulfide gives ca 30% yield of (C5H5)3Ni3(CS)2, a trimetallic cluster with a triply bridging thiocarbonyl ligands. Many other thiocarbonyl complexes arise from similarly complicated reactions in modest yield.[2]
A variety of other routes have been developed, including addition of sulfur reagents to metal carbyne complexes.[2]