Cation assisted binding and cleavage of dinitrogen by uranium complexes

Abstract

The role of alkali promoters in N2 cleavage by metal complexes remains poorly understood despite its relevance to the industrial production of ammonia from N2. Here we report a series...

Multimetallic Uranium Nitride Cubane Clusters from Dinitrogen Cleavage

“…Molecular nitride compounds were identified as important intermediates in the biological and industrial conversion of dinitrogen into ammonia and N-containing organic compounds, but the mechanism of N 2 cleavage to nitride remains unclear. − Because of their relevance as a precursor and model of inorganic uranium nitrides and in the understanding of uranium-ligand multiple bonding, the chemistry of molecular uranium nitride compounds has witnessed significant advances in the last 10 years. , The synthesis of molecular cluster analogs of uranium mononitride (UN) is important for modeling the properties of bulk UN, but most molecular uranium nitrides reported so far show a low nitride content (1 or 2 N 3– ligands) − with only two larger U 4 N 4 and U 8 N 4 clusters containing four nitride ligands. , Moreover, despite inorganic uranium compounds being reported to be efficient catalysts for N 2 conversion to ammonia, , only a few examples of multimetallic uranium nitrides were so far prepared from dinitrogen cleavage (clusters A–D in Figure ) ,,,, and only in one case intermediates containing less reduced N 2 species could be isolated …”

A trinuclear metallasilsesquioxane of uranium(iii)

“…Only a few examples of complexes showing unambiguous magnetic coupling between U( iii ) centres have previously been reported. 3,9,49,50 These results provide a rare example of structure-magnetic properties relation in uranium chemistry 51 showing that structural changes lead to dramatic differences in the magnetism of polynuclear U( iii ) complexes.…”

“…The design of polymetallic assemblies is attracting high interest in uranium chemistry because of their ability to promote small molecule activation, [1][2][3][4][5][6][7][8][9][10] and their interesting magnetic properties, [11][12][13][14][15] yet synthetic routes to such assemblies remain elusive. Moreover, the recent identification of the first example of actinide metal-metal bonding interactions in a trinuclear thorium complex 16,17 suggests that trinuclear assemblies may be used to promote metal-metal interactions in uranium compounds.…”

Progress in the chemistry of molecular actinide-nitride compounds

“…39,67 In a more recent study, Jori, Mazzanti and co-workers reported the reactivity of the analogous rubidium (Rb) and cesium (Cs) complexes, [M 2 (U III (OSi(O t Bu) 3 ) 3 ) 2 (μ-O)] (M = Rb ( 2-O ), Cs ( 3-O )) with N 2 (Scheme 2a). 61 The three alkali cations (K, Rb, Cs) display differences in the ability to bind N 2 , which are not correlated to differences found in the redox potentials of the three complexes, 61 but instead, a decrease with increasing size and decreasing Lewis acidity of the alkali ion binding to the U III –O–U III complex. Complex 1-O irreversibly reduces N 2 at ambient conditions, while N 2 is reversibly reduced by the Rb 2 U III –O–U III complex 2-O in the same conditions.…”

“…1,2 The N 2 chemistry of actinides is signicantly less developed, and typically involves labile N 2 binding, the 2e − reduction of N 2 , or more recent examples demonstrating the 4e − reduction by two U(III) complexes or dinuclear U(III)/U(III) species. 35,48,[54][55][56][57][58][59][60][61] Based on the structure of the nal nitride complex, multimetallic cooperation of transition metals and Lewis acids, potassium (K) in particular, was invoked to be crucial in the 6e − cleavage of N 2 to nitride involving alkali ions as reducing agents. 62,63 Notably, the rst actinide-nitride complex isolated in any signicant quantity was synthetized in 2002 by Gambarotta and co-workers via full reductive cleavage of N 2 , promoted by the reaction of the trivalent uranium complex, [K(DME)][(Et 8 -calix [4]tetrapyrrole) U III (DME)], with [K(naphthalenide)] under N 2 (A, Scheme 1).…”