There is currently great interest in the nature and reactivity of molecular uranium-ligand multiple bonds. This is because the nature and extent of 5f/6d orbital participation in uranium-ligand bonding is still a topic of debate and the unique orbital-hybridisation patterns available to uranium promises novel applications in atom-efficient catalysis and small molecule activation.Molecular uranium nitrides are of special interest because of their potential as precursors to uranium nitride materials via 'soft' routes, but perhaps more importantly because in contrast to commonly observed U=O, U=NR, and U=CR2linkages the U=N triple bond was prominent for its paucity. For example, the only examples of the U=N triple bond were previously confined to matrix isolation experiments at ~5 K and attempts to prepare molecular species under ambient conditions in exploitable quantities resulted in compounds where the nitride bridges to 2-4 metal atoms or is trapped by a covalently bound borane group. The U=N triple bond was proposed by calculations to be a transient species formed during photolysis of uranium(IV)-azides, but it could not be trapped and instead reacts with ancillary-ligand C-H bonds to give amide derivatives.Recently, we reported that a sterically encumbered uranium(III)-triamidoamine complex [U(TrenTIPS)] [TrenTIPS = N(CH2CH2SiPri3)3] reacts with sodium azide to afford the bridging uranium(V)-nitride complex [{U(TrenTIPS)(�-N)(�-Na)}2]. Abstraction and sequestration of the sodium ion by 12-crown-4 ether results in the separated ion pair complex [U(TrenTIPS)(N)][Na(12-crown-4)2] which contains the terminal U=N triple bond linkage under ambient conditions and in multi-gram quantities.We will discuss this chemistry and the factors that contributed to the success of this relatively simple strategy and will detail more recent work in this area including the isolation and reactivity of the long-sought terminal uranium(VI)-nitride triple bond, general reactivity studies, and magnetic behaviour.

Recent progress in molecular uranium nitride chemistry

247th National Meeting (2014)

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