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

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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.

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