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Transition metal dithiophosphate complex

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Transition metal dithiophosphate complex
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Transition metal dithiophosphate complexes are coordination compounds containing dithiophosphate ligands, i.e. ligands of the formula (RO)2PS−
2. The charge-neutral complexes tend to be soluble in organic solvents, especially when R is branched. Dithiophosphates are available with a wide variety of alkoxy groups. The range of complexes is similar to those for dithiocarbamate complexes.

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Structure of nickel bis(dimethyldithiophosphate).[1] Color code: green = Ni, yellow = S, orange = P, red = O. Selected distance and angles: P-S =198, P-O = 156, Ni-S = 222 pm and S-P-S = 103°, S-Ni-S = 88°.
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Preparation

Dithiophosphate ligands are prepared by alcoholysis of phosphorus pentasulfide:[2]

P4S10 + 8 C2H5OH → 4 (C2H5O)2PS2H + 2 H2S

Dialkoxydithiophoric acids react with many metal oxides, chlorides, and acetates:[2]

3 (C2H5O)2PS2H + CrCl3(H2O)6 → Cr[S2P(OC2H5)2]3 + 3 HCl + 6 H2O

Alternatively, salts, such as ammonium diethyldithiophosphate, can be used to prepare complexes by salt metathesis reactions:[3]

2 NH4[S2P(OC2H5)2] + NiCl2·(H2O)6 → Ni(S2P(OC2H5)2) + 6 H2O + 2 NH4Cl
3 NH4[S2P(OCH3)2] + MoCl3(thf)3 → Mo[S2P(OCH3)2]3 + 3 NH4Cl + 3 thf (thf = tetrahydrofuran)

Oxidation of dithiophosphoric acid gives the disulfide.[4] Dithiophosphate complexes have also be prepared by oxidative addition of these disulfides:[5]

[S2P(OC2H5)2]2 + Ni(P(OC6H5)3)4 → Ni(S2P(OC2H5)2)2 + 4 P(OC6H5)3
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Ligand properties

Dithiophosphates, when bidentate, are classified as L-X ligands in the Covalent bond classification method. In the usual electron counting method, they are three-electron ligands. With respect to HSAB theory, dithiophosphates are classified as soft ligands. In addition to the conventional representation, they are also described by a zwitterionic resonance structure (RO)2P+(S−)2. Phosphorus is tetrahedral.

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Selected homoleptic complexes

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Structure of an ligand (L) adduct of a typical zinc bis(dithiophosphate) complex. Such zinc dithiophosphate complexes are usually pentacoordinate.[6]

Homoleptic complexes have formulas M[S2P(OR)2]4, M[S2P(OR)2]3, and M[S2P(OR)2]2.

  • Zr[S2P(OC3H7)2]4[7]
  • V[S2P(OC2H5)2]3, red-brown,[8]
  • Cr[S2P(OC2H5)2]3, violet[9]
  • Mo[S2P(OCH3)2]3, red[3]
  • Fe[S2P(OC3H7)2]3[10]
  • Ru[S2P(OC2H5)2]3[11] pink, paramagnetic
  • Ir[S2P(OC3H7)2]3[12]
  • Ni[S2P(OC6H11)2]2[13] violet[14]
  • Pd[S2P(OC2H5)2]2[15]
  • Pt[S2P(OC2H5)2]2[4] yellow, diamagnetic[14]
  • Cu[S2P(OC6H4CH3)2]2[16]
  • poly-Zn[S2P(OC2H5)2]2[17]

These complexes are almost always solids at room temperature.

Applications

Zinc dialkyldithiophosphates are components of oil additives.[18][19] Dithiophosphate complexes are also implicated as intermediates in froth flotation, e.g. for the purification of copper from slag.[20]

References

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