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

Abstract

The {UO 2(DPPMO 2) 2} 2+ dication (where DPPMO 2 = bis(diphenylphosphino)methane) contains the linear uranyl group, {UO 2} 2+, with two bidentate P O donor ligands. Previously, we have shown that the weakly coordinating oxoanions [ReO 4] − and [TcO 4] − (as well as Cl −) will fill a fifth equatorial coordination site yielding complexes of general formula [UO 2(DPPMO 2) 2X][X] (where X = [ReO 4] −, [TcO 4] − 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, ((CF 3SO 2) 2N −, NTf 2 - ) and triflate ( CF 3 SO 3 - OTf −) anions and we report the structural characterisation of both [UO 2(NTf 2)(DPPMO 2) 2][NTf 2] ( 1) and [UO 2(OTf)(DPPMO 2) 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 − > [ReO 4] − > [OTf] − > [NTf 2] −. In addition, 31P{ 1H} NMR competition studies show that both nitrate and excess DPPMO 2 will readily displace the weakly coordinating X − anions.