The Reaction Chemistry of Plutonyl(VI) Chloride Complexes with Triphenyl Phosphineoxide and Triphenyl Phosphinimine

The reaction between Ph3PO dissolved in acetone and “PuO2Cl2” in dilute HCl resulted in the formation of [PuO2Cl2(Ph3PO)2]. Crystallographic characterization of the acetone solvate revealed the expected axial trans plutonyl dioxo, with trans Cl and Ph3PO in the equatorial plane. Spectroscopic analyses (31P NMR, 1H NMR, and vis/nIR) indicate the presence of both cis and trans isomers in solution, with the trans isomer being more stable. Confirmation of the higher stability of the trans versus cis isomers for [AnO2Cl2(Ph3PO)2] (An = U and Pu) was obtained through quantum chemical computational analysis, which also reveals the Pu−OTPPO bond to be more ionic than the U−OTPPO bond. Slight variation in reaction conditions led to the crystallization of two further minor products, [PuO2(Ph3PO)4][ClO4]2 and cis-[PuCl2(Ph3PO)4], the latter complex revealing the potential for reduction to PuIV. In addition, the reaction of Ph3PNH with [PuO2Cl2(thf)2]2 in anhydrous conditions gave evidence for the formation of both cis- and trans-[PuO2Cl2(Ph3PNH)2] in solution (by 31P NMR). However, the major reaction pathway involved protonation of the ligand with the crystallographic characterization of [Ph3PNH2]2[PuO2Cl4]. We believe that HCl/SiMe3Cl carried through from the small scale preparation of [PuO2Cl2(thf)2]2 was the source of both protons and chlorides. The fact that this chemistry was significantly different from previous uranium studies, where cis-/trans-[UO2Cl2L2] (L = Ph3PO or Ph3PNH) were the only products observed, provides further evidence of the unique challenges and opportunities associated with the chemistry of plutonium.