Synthesis, characterization and solution behaviour of phosphoryl complexes of tin tetrafluoride

The preparation and characterization of a series of octahedral complexes [SnF4L2] (L = (Me2N)3PO (1), L = (R2N)2P(O)F; R = Me (2); Et (3) or L = R2NP(O)F2; R = Me (4); Et (5)) are described. These new adducts have been characterised by multinuclear (19F, 31P and 119Sn) NMR, IR spectroscopy and elemental analysis. The NMR data particularly the 19F NMR spectra showed that the complexes exist in solution as mixtures of cis and trans isomers. The solution behaviour of the complexes studied by variable temperature NMR in the presence of excess ligand indicated that, unlike in the SnCl4 analogues, the ligand exchange at room temperature is slow for 1–3 and fast only for 4 and 5. The metal–ligand exchange barriers in [SnF4L2] and [SnCl4L2] systems were estimated and compared. The results indicate that in addition to the difference in the Lewis acidity between SnF4 and SnCl4 the nature of the substituents (fluorine atoms) on the phosphorus atom of the ligand can contribute considerably to the lability of the complex obtained.