A Single Small-Scale Plutonium Redox Reaction System Yields Three Crystallographically-Characterizable Organoplutonium Complexes

Abstract

An approach to obtaining substantial amounts of data from a hazardous starting material that can only be obtained and handled in small quantities is demonstrated by the investigation of a single small-scale reaction of cyclooctatetraene, C8H8, with a solution obtained from the reduction of Cp′3Pu (Cp′ = C5H4SiMe3) with potassium graphite. This one reaction coupled with oxidation of a product has provided single-crystal X-ray structural data on three organoplutonium compounds as well as information on redox chemistry thereby demonstrating an efficient route to new reactivity and structural information on this highly radioactive element. The crystal structures were obtained from the reduction of C8H8 by a putative Pu­(II) complex, (Cp′3PuII)1−, generated in situ, to form the Pu­(III) cyclooctatetraenide complex, [K­(crypt)]­[(C8H8)2PuIII], 1-Pu, and the tetra­(cyclopentadienyl) Pu­(III) complex, [K­(crypt)]­[Cp′4PuIII], 2-Pu. Oxidation of the sample of 1-Pu with Ag­(I) afforded a third organoplutonium complex that has been structurally characterized for the first time, (C8H8)2PuIV, 3-Pu. Complexes 1-Pu and 3-Pu contain Pu sandwiched between parallel (C8H8)2– rings. The (Cp′4PuIII)− anion in 2-Pu features three η5-Cp′ rings and one η1-Cp′ ring, which is a rare example of a formal Pu–C η1-bond. In addition, this study addresses the challenge of small-scale synthesis imparted by radiological and material availability of transuranium isotopes, in particular that of pure metal samples. A route to an anhydrous Pu­(III) starting material from the more readily available PuIVO2 was developed to facilitate reproducible syntheses and allow complete spectroscopic analysis of 1-Pu and 2-Pu. PuIVO2 was converted to PuIIIBr3(DME)2 (DME = CH3OCH2CH2OCH3) and subsequently PuIIIBr3(THF) x , which was used to independently synthesize 1-Pu, 2-Pu, and 3-Pu.

Cyclopentadienyl coordination induces unexpected ionic Am−N bonding in an americium bipyridyl complex

“…The synthesis of Cp′ 3 Am was achieved by means of established synthetic methods for the dehydration of actinides using Me 3 Si−Br followed by the salt metathesis reaction with KCp′ to form a putative Cp′ 3 Am residue 17 , 20 , 38 . Modeled on the structure of Mehdoui’s (Cp′ 3 U) 2 ( μ -4,4′-bpy), the addition of 4,4′-bpy to Cp′ 3 M in toluene results in an immediate precipitate 39 .…”

“…Deviations from an equidistant interaction such as in the M−Cp bonds are observed when a fourth ligand coordinates and/or a Cp derivative is used. The classic arrangement for the coordination of three Cp′ ligands to f -block ions corresponds to two – SiMe 3 groups facing up and the third facing down 20 . Therefore, the combination of coordinating Cp’ ligands and a fourth bulky ligand such as 4,4′-bpy makes the number of BCPs <5 (Supplementary Fig.…”

“…Historically, cyclopentadienide (Cp − = C 5 H 5 ) was used to synthesize the first transuranic organometallic complexes, and its derivatives, Cp tet (C 5 Me 4 H), Cp′ (C 5 H 4 SiMe 3 ), and Cp′′ [C 5 H 3 (SiMe 3 ) 2 ] have paved the way for solving the unusual bonding and redox chemistry observed in these elements 17 , 19 – 36 . Recent advances in transuranic synthesis have yielded the structural characterization of organometallic plutonium and americium complexes 17 , 19 , 20 . Single-crystal characterization of an organoamericium complex, [(C 5 Me 4 H) 3 Am], was obtained in 2019, and there is no published organometallic single-crystal characterization for elements heavier than americium to date 17 .…”

Structural and Spectroscopic Comparison of Soft‐Se vs. Hard‐O Donor Bonding in Trivalent Americium/Neodymium Molecules

“…Attempting to understand more subtle Am/Ln differences in a comparable study has been impeded by a lack of well‐developed Am synthetic chemistry methods along with radiological and isotope availability considerations. Recent advances in air‐/moisture‐free Am chemistry now permit us to compare hard O‐ and soft Se‐donor complexes, [12d, 14] [Am{N(E=PPh 2 ) 2 } 3 ] (E=Se, 1‐Am ; O, 2‐Am ), to their isoradial Nd congeners [Nd{N(E=PPh 2 ) 2 } 3 ] ( 1‐Nd , 2‐Nd ). We have examined the bonding and electronic structure in these complexes by single crystal X‐ray diffraction, UV‐vis‐NIR spectroscopy, multi‐nuclear NMR spectroscopy, and ab initio calculations.…”

Synthesis, characterization, and high-pressure studies of a 3D berkelium(iii) carboxylate framework material

“…Bk), 23 An III 2 (HPO 3 ) 3 (H 2 O) (An = Pu, Am), 24 and An III 2 (C 4 O 4 ) 3 (H 2 O) 4 (An = Am, Cf). 25 The opposite effect is found in softer donor systems such as An III (dtc) 3 (phen) (dtc À = diethyldithiocarbamate; phen = 1,10-phenanthroline, An = Am, Cm, Cf), 26 [K(crypt)][Pu III (COT) 2 ] (crypt = 2.2.2-cryptand, COT 2À = cyclooctatetrenide), 27 and An IV L 2 (H 2 L = N,N 0 -bis[(4,4 0 -diethylamine)salicylidene]-1,2-phenylenediamine, An = Th, U, Np, Pu) 28,29 where the actinide bond lengths fall significantly below the lanthanide-ligand bond trendline meaning the actinide bond lengths are shorter than expected based on their ionic radii.…”