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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 a zinc dithiophosphate complex.[1]

Important members are zinc dialkyldithiophosphates, which are oil additives.[2][3]

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Preparation

Dithiophosphate complexes are usually prepared by salt metathesis from preformed ligands. Dialkoxydithiophoric acid reacts with many metal oxides, chlorides, and acetates:[4]

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:

2 NH4[(S2P(OC2H5)2] + NiCl2·(H2O)6 → Ni(S2P(OC2H5)2) + 6 H2O + 2 NH4Cl

Dithiophosphate complexes have also be prepared by oxidative addition of their 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, they are classified as soft. In addition to the conventional representation, they are also described by a zwitterionic resonance structure (RO)2P+(S−)2.

Dithiophosphate ligands are prepared by alcoholysis of phosphorus pentasulfide:[4]

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

Alternatively, the intermediate dialkoxydithiophoric acid can be deprotonated to give salts, such as ammonium diethyldithiophosphate, which can also be used to prepare complexes:

(C2H5O)2PS2H + NH3 → NH4[(S2P(OC2H5)2]
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Selected homoleptic complexes

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

  • Ni[S2P(OC6H11)2]2[6] violet[7]
  • Cu[S2P(OC6H4CH3)2]2[8]
  • Pd[S2P(OC2H5)2]2[9]
  • Pt[S2P(OC2H5)2]2[10] yellow, diamagnetic[7]
  • Cri[S2P(OC2H5)2]3[11] violet, paramagneticx
  • Ru[S2P(OC2H5)2]3[12] pink, paramagnetic
  • Ir[S2P(OCH(CH3)2)2]3[13]

References

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