Synthesis and characterization of a platinum(II) complex of camphenylphosphonic acid

Abstract

Camphenylphosphonic acid RPO₃H₂, prepared by the literature reaction of PCl₅ with camphene, has been characterized by a single-crystal X-ray diffraction study. The compound crystallizes with a double chain structure formed by connected eight-membered hydrogen-bonded rings. Reaction of RPO₃H₂ with cis-[PtCl₂(PPh₃)₂] and excess silver(I) oxide in refluxing dichloromethane gives the platinum(II) phosphonate complex [Pt{O₃PR}(PPh₃)₂]. ³¹P{¹H} NMR spectroscopic characterization of [Pt{O₃PR}(PPh₃)₂] shows that the two PPh₃ ligands are inequivalent due to asymmetry of the camphenyl group. An X-ray diffraction study on the platinum complex shows that the PC–H bond is directed toward the four-membered ring, resulting in the terpene group pointing away from the ring, in contrast to the previously reported structure of the saturated camphanylphosphonate complex. The differences are discussed in terms of steric interactions involving the phosphonate ligands.

Keywords:

• Phosphonic acids
• Phosphonate complexes
• Terpenes
• Platinum complexes
• X-ray structure determinations

Acknowledgments

We thank the University of Waikato for the financial support of this work and Steven Alley for the preparation of camphenylphosphonic acid. We also thank Pat Gread for mass spectrometry support, Dr Jan Wikaira (University of Canterbury) for the collection of the X-ray data set of 3, and Dr Tania Groutso (University of Auckland) for the collection of the X-ray data set of 4.