Synthesis of Imido Analogs of the Uranyl Ion

Abstract

Here we describe the synthesis of two imido analogs of the uranyl ion, UO 2+ 2 , in which the oxygens are replaced by divalent alkyl or aryl nitrogen groups: U(N t Bu) 2 I 2 (THF) 2 (1) and U(NPh) 2 I 2 (THF) 3 (2) (where t Bu is tert -butyl and THF is tetrahydrofuran). Both compounds have been fully characterized by standard analytical techniques, including x-ray crystallography, and the chemical bonding between the metal center and the nitrogen ligands was quantified by using hybrid density functional theory calculations. As expected for a uranyl analog, these complexes exhibit linear N-U-N linkages and very short U-N bonds. In addition, the theoretical calculations show strong involvement of the 5f and 6d electrons in the U-N bonding.

Elucidating bonding preferences in tetrakis(imido)uranate(VI) dianions

“…In 2005, a major breakthrough was reported by Boncella and co-workers, who synthesized uranium(VI) trans-bis(imido) species-these feature strong U-N multiple bonds that make them directly analogous to uranyl derivatives 7 . A significant difference between the two classes is that the imido analogues show increased covalency as compared with the parent uranyl compounds, with a greater participation of uranium 5f orbitals involved in bonding as compared with the oxygen congeners 8 .…”

“…In these derivatives, the bond distances along the trans-N ax =U=N ax (ax, axial) axis (1.992(5) Å) are contracted with respect to the corresponding distance for the equatorial imido substituent (2.024(5) Å), which is expected based on the inverse trans influence found in actinide bonding. What was surprising is that a computational analysis showed that a π contribution of the equatorial imido into the σ-bonding orbital of the N ax =U=N ax unit ultimately results in a significant ∼0.1 Å lengthening as compared with U(NR′) 2 I 2 (THF) n (R′, Ph, t Bu) 7 . Subsequent generation of a uranium tris(imido) complex that lacked traditional bulky ancillary ligands, U(NDIPP) 3 (THF) 3 (1) 18 , was accomplished, and structural characterization revealed a facial ( fac)-octahedral uranium ion in which no imido groups were oriented trans to each other (U-N, 1.986(14)-2.010(15) Å), suggesting the preference for the trans orientation was overcome by heavy π donation.…”

Triamidoamine uranium(IV)–arsenic complexes containing one-, two- and threefold U–As bonding interactions

“…Uranium is one actinide that is amenable to routine study, and uranium-ligand multiple-bond complexes have attracted attention because they would be expected to contain some covalency 13-15 . Recently, in addition to the numerous uranium-oxo derivatives, for example uranyl 16 , there have been advances in the synthesis, characterization and understanding of covalent, terminal uraniumcarbene [17][18][19][20][21][22] , -imido [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] , -nitride [38][39][40] , -phosphinidene [41][42][43] and heavier-chalcogenide 44,45 multiple bonds. Nevertheless, carbon, nitrogen and oxygen donor ligands dominate, and post-first-row donor ligands remain relatively rare and sharply decrease in number as the periodic table is descended.…”

Formation of unprecedented actinidecarbon triple bonds in uranium methylidyne molecules

“…Whereas numerous organic and inorganic compounds with multiple bonds are known (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), f elements (lanthanides and actinides) with multiple bonds are relatively rare, except for early actinides. Such bonding has aroused great interest recently in the search for actinide complexes with multiple bonds between two actinide metals (18)(19)(20)(21) and between actinide (An) and main-group ligands (L) (22)(23)(24)(25)(26)(27)(28).…”

“…Among the actinide complexes with An-L multiple bonds, the importance of first-row elements to bond to actinide metal centers has been highlighted by Burns (22), and molecular complexes containing metal-nitride units have been prepared recently (24)(25)(26). Uranium as the leading example forms a plethora of UϭO bonds and a handful of UϭNR and UϭCR 2 (R ϭ organic groups) bonds.…”