Identification of the stereochemistry of square planar bis-triethylphosphine complexes by infrared spectroscopy

Abstract

The infrared spectra of cis-(Me₃P)₂PtBr₂, trans-(Me₃P)₂Ptl₂, and Et₃P are discussed with a view to assisting in the identification of platinum–phosphorus stretching frequencies in triethylphosphine complexes. For trans-(Et₃P)₂PtCl₂, the infrared-active metal–phosphorus stretching frequency is found at 415 cm.^–1 while the symmetrical stretching frequency was observed in the Raman spectrum with a shift of 443 cm.^–1. For cis-(Et₃P)₂PtCl₂, the two infrared-active stretching frequencies are found at 442 and 427 cm.^–1. This distinction has been used to determine the stereochemistry of a number of derivatives (Et₃P)₂PtX₂(X = Br, I, NCS, CN, Ph, or C₆F₅).

It is found that the infrared-active metal–phosphorus stretching frequencies in nickel and palladium compounds are within 6 cm.^–1 of the stretching frequencies for the corresponding platinum compounds. By this means, a cis-bistriethylphosphine derivative of palladium, cis-(Et₃P)₂Pd(C₆F₅)₂, has been identified for the first time. All the other palladium and nickel derivatives were shown to have the trans-configuration.

Some unsymmetrical derivatives, (Et₃)₂MXY (M = Ni, Pd, or Pt; X = Cl, Br, I, or Me; Y = Ph or C₆F₅), have also been investigated. In spite of the fact that the trans-derivatives are not centrosymmetric, only one metal–phosphorus absorption could be identified.