Coordination of bistriflimide and triflate to the uranyl bis(diphenylphosphino)methane dication, {UO2(DPPMO2)2}2+

The {UO2(DPPMO2)2}2+ dication (where DPPMO2 = bis(diphenylphosphino)methane) contains the linear uranyl group, {UO2}2+, with two bidentate PO donor ligands. Previously, we have shown that the weakly coordinating oxoanions [ReO4]− and [TcO4]− (as well as Cl−) will fill a fifth equatorial coordination site yielding complexes of general formula [UO2(DPPMO2)2X][X] (where X = [ReO4]−, [TcO4]− and Cl−), with the X− anion acting in both monodentate coordinated and uncoordinated modes. Seven coordinate pentagonal bipyramidal uranyl complexes with the same general formula have now also been prepared with both the bistriflimide, ((CF3SO2)2N−, NTf2-) and triflate (CF3SO3- OTf−) anions and we report the structural characterisation of both [UO2(NTf2)(DPPMO2)2][NTf2] (1) and [UO2(OTf)(DPPMO2)2][OTf] (2). In the case of 1 the anion is coordinated through a terminal oxygen, representing the first structural characterization of an actinide-bistriflimide complex. Both the solid state uranium-anion bond lengths (for O-donor ligands only) and 31P{1H} NMR solution competition studies indicate that the strength of the uranyl-anion bond decreases along the series Cl− > [ReO4]− > [OTf]− > [NTf2]−. In addition, 31P{1H} NMR competition studies show that both nitrate and excess DPPMO2 will readily displace the weakly coordinating X− anions.

We report the structural characterization of [UO2(NTf2)(DPPMO2)2][NTf2] (NTf2- = bistriflimide) and [UO2(OTf)(DPPMO2)2][OTf] (OTf− = triflate). In addition, a spectroscopic and structural investigation of a series of [UO2(X)(DPPMO2)2]+ complexes indicates that the strength of the uranium to X− ligand bonding interaction decreases along the series [Cl]− > [ReO4]− > [OTf]− > [NTf2-].Figure optionsDownload as PowerPoint slide