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Tetrakis(triphenylphosphine)platinum(0)

Tetrakis(triphenylphosphine)platinum(0) is the chemical compound with the formula Pt(P(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>)<sub>4</sub>, often abbreviated Pt(PPh<sub>3</sub>)<sub>4</sub>. The bright yellow compound is used as a precursor to other platinum complexes.

Structure and behavior

The molecule is tetrahedral, with point group symmetry of T<sub>d</sub>, as expected for a four-coordinate metal complex of a metal with the d<sup>10</sup> configuration. Even though this complex follows the 18 electron rule, it dissociates triphenylphosphine in solution to give the 16e<sup>−</sup> derivative containing only three PPh<sub>3</sub> ligands:

Pt(PPh<sub>3</sub>)<sub>4</sub> → Pt(PPh<sub>3</sub>)<sub>3</sub> + PPh<sub>3</sub>

Synthesis and reactions

The complex is typically prepared in one-pot reaction from potassium tetrachloroplatinate(II). Reduction of this platinum(II) species with alkaline ethanol in the presence of excess triphenylphosphine affords the product as a precipitate. The reaction occurs in two distinct steps. In the first step, PtCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub> is generated. In the second step, this platinum(II) complex is reduced. The overall synthesis can be summarized as:

K<sub>2</sub>[PtCl<sub>4</sub>] + 2KOH + 4PPh<sub>3</sub> + C<sub>2</sub>H<sub>5</sub>OH → Pt(PPh<sub>3</sub>)<sub>4</sub> + 4KCl + CH<sub>3</sub>CHO + 2H<sub>2</sub>O

Pt(PPh<sub>3</sub>)<sub>4</sub> reacts with oxidants to give platinum(II) derivatives:

Pt(PPh<sub>3</sub>)<sub>4</sub> + Cl<sub>2</sub> → cis-PtCl<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub> + 2 PPh<sub>3</sub>

Mineral acids give the corresponding hydride complexes:

Pt(PPh<sub>3</sub>)<sub>4</sub> + HCl → trans-PtCl(H)(PPh<sub>3</sub>)<sub>2</sub> + 2 PPh<sub>3</sub>

The reaction with oxygen affords a dioxygen complex:

Pt(PPh<sub>3</sub>)<sub>4</sub> + O<sub>2</sub> → Pt(η<sup>2</sup>-O<sub>2</sub>)(PPh<sub>3</sub>)<sub>2</sub> + 2 PPh<sub>3</sub>

This complex is a precursor to the ethylene complex

Pt(η<sup>2</sup>-O<sub>2</sub>)(PPh<sub>3</sub>)<sub>2</sub> + C<sub>2</sub>H<sub>4</sub> → Pt(η<sup>2</sup>-C<sub>2</sub>H<sub>4</sub>)(PPh<sub>3</sub>)<sub>2</sub> + "NaBH<sub>2</sub>(OH)<sub>2</sub>"

References