Fluorophosphine complexes of rhodium(I). Part II. Phosphine exchange studies

Abstract

Trifluorophosphine readily displaces ethylene from [RhCl(C₂H₄)₂]₂ under mild conditions affording high yields of the red, volatile, dimeric complex [RhCl(PF₃)₂]₂, (I). The ¹⁹F n.m.r. spectrum of (I) has been fully analysed as the X part of an [X₃A]₂ spin system (X = fluorine, A = phosphorus). A rapid intermolecular exchange between free and co-ordinated PF₃ has been observed in this system. The binuclear complex [RhCl(C₂H₄)(PF₃)]₂, (II), formed by mixing solutions containing equimolar amounts of [RhCl(C₂H₄)₂]₂ and [RhCl(PF₃)₂]₂ has been shown to have one ethylene and one trifluorophosphine group attached to each rhodium atom. Complex (I) reacts with an excess of carbon monoxide quantitatively forming [RhCl(CO)₂]₂, whereas triphenylphosphine cleaves the halogen bridge affording the square planar complex RhCl(PF₃)(PPh₃)₂, (III). Complex (III) has also been obtained directly from RhCl(PPh₃)₃ and trifluorophosphine. ¹⁹F n.m.r. studies establish the trans-stereochemistry of (III) and indicate that the complex does not dissociate in solution. However (III) does undergo a ready intermolecular exchange of its co-ordinated PF₃ and PPh₃ ligands. Difluorotrichloromethylphosphine completely displaces ethylene or trifluorophosphine from [RhCl(C₂H₄)₂]₂ and [RhCl(PF₃)₂]₂ respectively affording [RhCl(CCl₃PF₂)₂]₂. RhCl(PPh₃)₃ reacts with CCl₃PF₂ to yield RhCl(CCl₃PF₂)(PPh₃)₂.