Determination of the magnitudes and signs of phosphorus–phosphorus coupling (2Jpp) by hydrogen-1{phosphorus-31} internuclear double resonance measurements on some gold(I), iridium(III), mercury(II), palladium(II), platinum-(II) and -(IV), and rhodium(III) complexes containing two, three, or four trialkylphosphine ligands

Abstract

The application of ¹H{³¹P} INDOR spectroscopy to the evaluation of P–P coupling in a number of complexes has been investigated. The sign of ²J_PP(cis) for the complexes cis-[MX₂(PMe₃)₂], cis-[MX₂{P(OMe)₃}₂](M = Pd or Pt; X = Cl, Br, or I), and cis-[PtMe₂(PMe₃)₂] has been determined by comparison of observed and calculated ¹H{³¹P} INDOR spectra. The sign and magnitude of ²J_PP(trans) in the complexes trans-[MX₂(PMe₃)₂](M = Pd or Pt; X = Cl, Br, I, or CN), trans-[MX₂(PEt₃)₂](M = Pd or Pt; X = Cl, Br, or I), trans-[PtX₄(PMe₃)₂], [MX(PMe₃)₃]⁺(M = Pd or Pt), mer-[PtX₃(PMe₃)₃]⁺, mer-[RhX₃(PMe₃)₃], and trans-[PtX₄(PEt₃)₂](X = Cl or Br), trans-[IrCl₄(PMe₃)₂]^–, mer-[IrCl₃(PMe₃)₃], [Hg(PMe₃)₂]²⁺, [Au(PMe₃)₂]⁺, trans-[PtBr₂(PPrⁿ₃)₂], and trans-[Pdl₂{P(OMe)₃}₂] have been obtained using increased irradiating powers. Signs and magnitudes of both ²J_PP(cis) and ²J_PP(trans) have similarly been determined for the complexes trans-[RhX₂(PMe₃)₄]⁺ and trans-[IrX₂(PMe₃)₄]⁺(X = Cl or Br), [Pt(PMe₃)₄]²⁺, and [Pt{P(OMe)₃}₄]²⁺. All the trans-couplings are positive and greater than 250 Hz, whilst the cis-couplings are much smaller and negative except for those of the complex cis-[PdX₂{P(OMe)₃}₂]. Vibrational spectra of the latter complexes have been recorded and it is suggested that there may be something abnormal about their structure. The difference between the values of ²J_PP in corresponding PMe₃ and PEt₃ complexes is discussed.