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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]
Preparation
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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:[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 other complicated reactions in modest yield.[2]
A variety of other routes have been developed, including addition of sulfur reagents to metal carbyne complexes.[2]
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Structure and bonding
According to the Covalent bond classification method, terminal CS is classified as an L ligand, i.e., a charge-neutral Lewis base. With respect to HSAB theory, it is classified as soft. According to spectroscopic measurements, CS is a superior pi-acceptor relative to CO, as indicated by the shortness of M-CS vs M-CO bonds.[2]
Selenocarbonyl and tellurocarbonyl complexes
Several complexes of CSe and CTe have been characterized.[6] The first examples were prepared from the osmium dichlorocarbene complex.[7]
- OsCl2(CCl2)(PPh3)2(CO) + 2 EH− → OsCl2(CE)(PPh3)2(CO) + 2 Cl− + H2E (E = Se, Te; Ph = C6H5)
References
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