Abstract
Molecules containing actinide-nitrogen multiple bonds are of current interest as simple models for new actinide nitride nuclear fuels, and for their potential for the catalytic activation of inert hydrocarbon C-H bonds. Complexes with up to three uranium-nitrogen double bonds are now being widely studied, yet those with one thorium-nitrogen double bond are rare, and those with two are unknown. A new, simple mono(imido) thorium complex and the first bis(imido) thorium complex, K[Th(═NAr)N″3] and K2[Th(═NAr)2N″2], are readily made from insertion reactions (Ar = aryl, N″ = N(SiMe3)2) into the Th-C bond of the cyclometalated thorium amides [ThN″2(N(SiMe3)(SiMe2CH2))] and K[ThN″(N(SiMe3)(SiMe2CH2))2]. X-ray and computational structural analyses show a "transition-metal-like" cis-bis(imido) geometry and polarized Th═N bonds with twice the Wiberg bond order of the formally single Th-N bond in the same molecule.
Highlights
S trong and covalent multiple bond formation between actinide cations and oxo groups is a ubiquitous feature of actinide chemistry, most famously represented by the linear O U O unit in the uranyl dication [UO2]2+, in which the ligating atoms strongly donate electron density to the metal through one σ bond and two π bonds in an unreactive and formally triple bond.[1]
Their bonding has been studied in terms of proving molecular analogues of actinide nitride nuclear fuels,[6] and their reactivities have been studied in the search for catalytic properties which might differ from those of the d-block complexes.[7]
An intramolecular ligand C−H bond addition reaction was initiated by diazoalkane binding to a UVI NR bond in the complex (C5Me5)2U( NC6H2tBu3)(N2CPh2),[8] the strong donation of the N(2p) orbitals and involvement of the uranium 5f orbitals is not conducive to the most desirable intermolecular hydrocarbon C−H bond addition chemistry, for which the more polar transition metal M N bonds have been celebrated.[9]
Summary
Communication thorium complex, [K2(S)x][Th( NDipp)2N′′2] (3), are both readily accessible from the simple, well-known thorium amidometallacycle, Th{N(Si′)(SiMe2CH2)}N′′2 (A) and a doubly metalated analogue, K[Th{N(Si′)(SiMe2CH2)}2N′′] (1) These are the first thorium-imido-containing complexes to be isolated without the support of the sterically constraining, clam-shellshaped bis(cyclopentadienyl) ligand set. The Th N bond orders calculated by DFT (Wiberg) methods are twice the value of the single Th−N amido bonds in the same molecule, suggesting a much more polar Th N bond than compared with uranium analogues, more like some of the most reactive early d-block M N complexes Both experiments and calculations suggest the potential for reactivity closer to the transition-metal imido complexes that can activate hydrocarbon C−H bonds.
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