Synthesis, structural characterisation and solution behaviour of high symmetry lanthanide triflate complexes with the sterically demanding phosphine oxides Cy3PO and tBu3PO

The synthesis and characterisation of lanthanide trifluoromethane sulfonate (Ln(OTf)3) complexes with tricyclohexylphosphine oxide, (Cy3PO) and tritert-butylphosphine oxide, (tBu3PO) is described. The structures of [Ln(H2O)5(Cy3PO)2].2R3PO.[OTf]3 (Ln = Pr, Tm R = Cy Ln = Nd R = tBu) are pentagonal bipyramidal with an equatorial plane of five H2O and two axial Cy3PO. The remaining Cy3PO molecules are hydrogen bonded to the coordinated water molecules as are the triflate anions. Solution NMR spectroscopy shows the triflate ions remain associated with the complexes in CDCl3 solution. Lanthanide induced shifts in the 19-F and 31-P NMR spectra confirm that one structure is present for all the lanthanides with an additional structure for the heavier metals. The acidity of the complexes has been examined by 31-P NMR spectroscopy of the reactions between [Ln(H2O)5(Cy3PO)2].2Cy3PO.[OTf]3 (Ln = La, Eu, Er, Lu) and phosphines PR3 (R = Ph, mesityl and Cy) and Ph2PC2H4PPh2 and Ph2PC3H6PPh2 . Protonation of the more basic phosphines and H-bonding to the less basic phosphines is observed.