The coordination chemistry of perfluorovinyl substituted phosphine ligands, a crystallographic and spectroscopic study. Co-crystallisation of both cis- and trans-isomers of [PtCl2{PiPr2(CFCF2)}2] within the same unit cell

Abstract

The coordination chemistry of the perfluorovinyl phosphines PEt₂(CFCF₂), PⁱPr₂(CFCF₂), PCy₂(CFCF₂) and PPh(CFCF₂)₂ to rhodium(I), palladium(II), and platinum(II) centres has been investigated. The electronic properties of the ligands are estimated based on ν(CO) and ¹J(Rh–P) values. X-Ray diffraction data for the square-planar Pd(II) and Pt(II) perfluorovinyl-phosphine containing complexes allow estimates of the steric demand for the series of ligands PPh₂(CFCF₂), PEt₂(CFCF₂), PⁱPr₂(CFCF₂), PCy₂(CFCF₂) and PPh(CFCF₂)₂ to be determined. The (CFCF₂) fragment is found to be more electron withdrawing than (C₆F₅) yet sterically less demanding. These ligands therefore provide a range of electron-neutral to phosphite-like electronic properties combined with a range of steric demands. This study also reveals that short intramolecular interactions from the metal centre to the β-fluorine atom cis to phosphorus of the CFCF₂groups are observed in all-trans square planar complexes of the ligands. Unusually, the complex [PtCl₂{PⁱPr₂(CFCF₂)}₂] crystallises with both cis- and trans-isomers present in the unit cell. It appears that co-crystallisation of both isomers occurs in order to maximise fluorous regions in the crystal packing, and the extended structure displays short fluorine–fluorine contacts. The generation of mixed geometries seems to be a phenomenon of crystallisation, as solution phase NMR studies reveal the presence of only the trans-isomer.