Transition metal dithiocarbamate complexes explained

thumb|193px|Structure of iron tris(diethyldithiocarbamate).

Transition metal dithiocarbamate complexes are coordination complexes containing one or more dithiocarbamate ligand, which are typically abbreviated R₂dtc⁻. Many complexes are known. Several homoleptic derivatives have the formula M(R₂dtc)_n where n = 2 and 3.^[1]

Ligand characteristics

Dithiocarbamates are anions. Because of the pi-donor properties of the amino substituent, the two sulfur centers show enhanced basicity. This situation is represented by the zwitterionic resonance structure that depicts a positive charge on N and negative charges on both sulfurs. This N to C pi-bonding results in partial double bond character. Consequently, barriers to rotational about this bond are elevated. Another consequence of their high basicity, dithiocarbamates often stabilize complexes in uncharacteristically high oxidation state (e.g., Fe(IV), Co(IV), Ni(III), Cu(III)).

Dithiocarbamate salts are easily synthesized. Many primary and secondary amines react with carbon disulfide and sodium hydroxide to form dithiocarbamate salts:^[2]

R₂NH + CS₂ + NaOH → R₂NCS₂⁻Na⁺ + H₂O

A wide variety of secondary amines give the corresponding dtc ligand. Popular amines include dimethylamine (Me₂NH), diethylamine (Et₂NH), and pyrrolidine ((CH₂)₄NH).

Related ligandsDithiocarbamates are classified as derivatives of dithiocarbamic acid. Their properties as ligands resemble the conjugate bases of many related "1,1-dithioacids":

• Xanthates, ROCS₂⁻
• Dithiophosphates, (RO)₂PS₂⁻
• Dithiocarboxylates, RCS₂⁻

Synthetic methods

Commonly, metal dithiocarbamates are prepared by salt metathesis reactions using alkali metal dithiocarbamates:

NiCl₂ + 2NaS₂CNMe₂ → Ni(S₂CNMe₂)₂ + 2NaClIn some cases, the dithiocarbamate serves as a reductant, followed by its complexation.^[3]

A complementary method entails oxidative addition of thiuram disulfides to low-valent metal complexes:

Mo(CO)₆ + 2[S₂CNMe₂]₂ → Mo(S₂CNMe₂)₄ + 6CO

Metal amido complexes, such as tetrakis(dimethylamido)titanium, react with carbon disulfide:

Ti(NMe₂)₄ + 4CS₂ → Ti(S₂CNMe₂)₄

Homoleptic complexes

Bis complexes

• nickel bis(dimethyldithiocarbamate), palladium bis(dimethyldithiocarbamate), platinum bis(dimethyldithiocarbamate),^[4] all square-planar complexes
• copper bis(diethyldithiocarbamate), a square-planar complex^[5]

Tris complexes

• vanadium tris(diethyldithiocarbamate), an octahedral complex^[6]
• chromium tris(diethylditiocarbamate), an octahedral complex^[7]
• manganese tris(dimthylthtiocarbamate), an octahedral complex^[8]
• iron tris(diethyldithiocarbamate), ruthenium tris(diethyldithiocarbamate), osmium tris(diethyldithiocarbamate), all octahedral complexes
• cobalt tris(diethyldithiocarbamate), rhodium tris(diethyldithiocarbamate), iridium tris(diethyldithiocarbamate), all octahedral complexes

Tetrakis complexes

• titanium tetrakis(dimethyldithiocarbamate)^[9]
• molybdenum tetrakis(diethyldithiocarbamate)

Dimetallic complexes

• iron bis(diethyldithiocarbamate), pentacoordinate Fe dimer
• zinc bis(dimethyldithiocarbamate), pentacoordinate Zn dimer
• dicobalt pentakis(diethyldithiocarbamate) cation, with a pair of octahedral Co(III) centers^[10]
• diruthenium pentakis(diethyldithiocarbamate) cation, with a pair of octahedral Ru(III) centers, two isomers

Reactions

Dithiocarbamate complexes do not undergo characteristic reactions. They can be removed from complexes by oxidation, as illustrated by the iodination of the iron tris(diethyldithiocarbamate):

They degrade to metal sulfides upon heating.^[11]

Applications

Dtc complexes find several applications:

• herbicides in the form of the iron and zinc derivatives Ferbam and Zineb, respectively
• vulcanization accelerators, zinc bis(dimethyldithiocarbamate).
• medicine, iron tris(dimethyldithiocarbamate) as a nitric oxide scavenger.
• lubricants. Metal thiocarbamates are also used in metal-to-metal lubrication proposes, mainly as an anti-oxidation or anti-extreme pressure (EP) additive. 1-2% of such compounds can be added to internal combustion engine lubricant to increase extreme pressure performance in high operational temperatures.^{[12] [13]}

Notes and References

1. Coucouvanis. Dimitri . The Chemistry of the Dithioacid and 1,1-Dithiolate Complexes, 1968–1977. Prog. Inorg. Chem. . Progress in Inorganic Chemistry . 1979 . 26. 301–469 . 10.1002/9780470166277.ch5. 9780470166277 .
2. Encyclopedia: Dithiocarbamic Acid and Derivatives. Ullmann's Encyclopedia of Industrial Chemistry. Rüdiger Schubart. 2000. 10.1002/14356007.a09_001. Wiley-VCH. 3527306730 . Weinheim.
3. 10.1002/9780470132470.ch2 . Dithiocarbamate Complexes of Iron and Cobalt Nitrosyls . Inorganic Syntheses . 1976 . Ileperuma . O. A. . Feltham . R. D. . 16 . 5–8 . 978-0-470-13178-7 .
4. 10.1021/acs.inorgchem.8b00724. Variation of M···H–C Interactions in Square-Planar Complexes of Nickel(II), Palladium(II), and Platinum(II) Probed by Luminescence Spectroscopy and X-ray Diffraction at Variable Pressure. 2018. Poirier. Stéphanie. Lynn. Hudson. Reber. Christian. Tailleur. Elodie. Marchivie. Mathieu. Guionneau. Philippe. Probert. Michael R.. Inorganic Chemistry. 57. 13. 7713–7723. 29893549. 48355413 .
5. 10.1016/j.molstruc.2017.01.021. Synthesis, Structures and Properties of Three Copper Complexes with Dibutyldithiocarbamate Ligand. 2017. Wang. Chen. Niu. Jiao. Li. Jun. Ma. Xiaoxun. Journal of Molecular Structure. 1135. 75–81. 2017JMoSt1135...75W.
6. 10.1107/S0108270196015065. Tris(N,N-diethyldithiocarbamato-S,S')vanadium(III). 1997. Zhu. H.-P.. Deng. Y.-H.. Huang. X.-Y.. Chen. C.-N.. Liu. Q.-T.. Acta Crystallographica Section C Crystal Structure Communications. 53. 6. 692–693.
7. 10.1071/CH9772091. Crystal Structure of Tris(N,N-diethyldithiocarbamato)chromium(III). 1977. Raston. CL. White. AH. Australian Journal of Chemistry. 30. 9. 2091.
8. 10.1107/S0108270186094635. A Second Polymorph of Tris(N,N-diethyldithiocarbamato)manganese(III). 1986. Elliot. R. L.. West. B. O.. Snow. M. R.. Tiekink. E. R. T.. Acta Crystallographica Section C Crystal Structure Communications. 42. 6. 763–764.
9. 10.1039/DT9720001052. Structural studies of metal dithiocarbamates. Part VI. The crystal and molecular structure of tetrakis(NN-diethyldithiocarbamato)titanium(IV). 1972. Colapietro. M.. Vaciago. A.. Bradley. D. C.. Hursthouse. M. B.. Rendall. I. F.. Journal of the Chemical Society, Dalton Transactions. 10. 1052.
10. 10.1039/dt9750002182. Synthesis and Properties of Dimeric Cobalt(III) Dithiocarbamate Complexes [Co₂(R₂dtc)₅]⁺: X-Ray Structural Analysis of Pentakis(diethyldithiocarbamato)dicobalt(III) Tetrafluoroborate. 1975. Hendrickson. Alan R.. Martin. Raymond L.. Taylor. Donald. Journal of the Chemical Society, Dalton Transactions. 21. 2182.
11. 10.1021/acs.chemrev.0c01183. Dithiocarbamate Complexes as Single Source Precursors to Nanoscale Binary, Ternary and Quaternary Metal Sulfides . 2021 . Sarker . Jagodish C. . Hogarth . Graeme . Chemical Reviews . 121 . 10 . 6057–6123 . 33847480 . 233222937 .
12. 10.1007/s11249-011-9855-x . Novel Alkylborate–Dithiocarbamate Lubricant Additives: Synthesis and Tribophysical Characterization . 2012 . Shah . Faiz Ullah . Glavatskih . Sergei . Antzutkin . Oleg N. . Tribology Letters . 45 . 67–78 . 98677629 .
13. 10.22078/jpst.2016.669. 2016. 6. 2. Shekarriz. Marzieh. An Investigation of Antioxidant Properties of Zinc and Molybdenum Dithiocarbamates in Hydrocarbons. Journal of Petroleum Science and Technology.