Uranium versus Thorium: Synthesis and Reactivity of [η⁵‐1,2,4‐(Me₃C)₃C₅H₂]₂U[η²‐C₂Ph₂]

Abstract

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η5‐1,2,4‐(Me3C)3C5H2]2U=P‐2,4,6‐tBu3C6H2 (1) yields the stable uranium metallacyclopropene, [η5‐1,2,4‐(Me3C)3C5H2]2U[η2‐C2Ph2] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U‐(η2‐C=C) moiety increases significantly compared to the related ThIV compound [η5‐1,2,4‐(Me3C)3C5H2]2Th[η2‐C2Ph2], which also results in more covalent bonds between the [η5‐1,2,4‐(Me3C)3C5H2]2U2+ and [η2‐C2Ph2]2− fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low‐valent uranium(II) metallocene [η5‐1,2,4‐(Me3C)3C5H2]2UII when reacted with Ph2E2 (E=S, Se), alkynes and a variety of hetero‐unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five‐membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones.

Influence of the 1,2,4-Tri-tert-butylcyclopentadienyl Ligand on the Reactivity of the Uranium Bipyridyl Metallocene [η5-1,2,4-(Me3C)3C5H2]2U(bipy)

“…A more elegant approach relies on well-defined organometallic actinide compounds, that do not possess a divalent oxidation state but serve as An­(II) synthons in the presence of suitable substrates. This allows the reactivity of An­(II) compounds to be evaluated, while evading the synthetic challenges associated with these difficult to access oxidation states . Redox-active ligands with energetically relatively low-lying acceptor orbitals such as 2,2′-bipyridine, 1,4-diazabutadiene, pyridine diimine, and arenes are particularly well suited for the latter approach since they may “store” or deliver electrons when needed.…”

Progress of Azametallacyclopentadienes in the New Century

“…[38] Later, they also found that the comparable uranacyclopropene 7 b could undergo similar insertion of nitrile to afford azauranacyclopentadiene 8 b. [40] Interestingly, when more sterically encumbered nitriles, such as CyCN and Ph 2 CHCN were employed, the alkyne dissociation and nitrile-nitrile coupling occurred to give the diazauranacyclopentadienes. In 2021, we reported the reaction of lutetacyclopropene 9 towards nitriles to give azalutetacyclopentadienes 10.…”

“…For example, when the reaction between uranacyclopropene 8 b and benzyl nitrile (PhCH 2 CN) was conducted, uranacyclic enamine 15 was obtained, instead of azauranacyclopentadiene 14. [40] The formation of 15 probably proceeds through the insertion of PhCH 2 CN into the UÀ C(sp 2 ) bond of 8 b to give 14, and the following tautomerization via intramolecular 1,3-H shift providing 15 (Scheme 3b). Similarly, the reactions of lutetacyclopropene 9 towards one equiv.…”

Selective C–C coupling of two nitriles affording rare-earth diazametallacyclopentadienes: synthesis, cooperative reactivity and mechanistic studies

“…To realize the assembly of two nitriles into diazametallacyclopentadienes, a suitable two-electron reductant of rare-earth species should be considered. [19][20][21][22][23]33,34 Because of the strong reducing ability of the reduced naphthalene ligand, the reduced naphthalene complexes of rare-earth metals were deemed as the precursors. [35][36][37][38][39][40][41][42][43][44] Herein, the selective C-C coupling of nitriles promoted by rare-earth metal reduced naphthalene complexes G was realized, affording the first rare-earth diazametallacyclopentadienes D via azametallacyclopropene intermediates I (Scheme 1c).…”