Carbon Monoxide and Isocyanide Complexes of Trivalent Uranium Metallocenes

[Am(C5Me4H)3]: An Organometallic Americium Complex

“…We observed disorder in 1 that is best described as both the left‐ and right‐handed molecules superimposed, but this was not observed in our structural determination of 2‐Ce . The Am(1)⋅⋅⋅Cp centroid distance of 2.517(8) Å is similar to M⋅⋅⋅Cp centroid distances observed for metals with similar ionic radii (coordination number 6, M 3+ ; Nd, 0.983 Å; U, 1.025 Å; Am 0.975 Å); 2.518(1) Å for Nd and 2.523(2) Å for U . This result, whereby the M⋅⋅⋅Cp centroid distance in both 1 and 2‐Nd are statistically equivalent is expected.…”

The Crucial Role of the f Electrons in the Bent or Linear Configuration of Uranium Cyanido Metallocenes

“…The average UC(Cp*) and UC(CN) bond lengths in 2 are smaller by about 0.1 Å than those in 1 , in agreement with the variation in the radii of the U 4+ and U 3+ ions 6. The UC(CN) bond lengths in 2 are larger than those in [(C 5 H 2 t Bu 3 ) 2 U(OSiMe 3 )(CN)] (2.415(6) Å)3 and in [(C 5 HMe 4 ) 3 U(CN) 0.6 (Cl) 0.4 ] (2.31(4) Å),4 thus reflecting the higher coordination number and negative charge of the anionic compound.…”

“…The cyanide anion was particularly attractive since, like MeCN, its suitable size and shape would permit the complete filling of the equatorial girdle of the {Cp* 2 U} 2+ moiety. The choice of this ligand was also motivated by the possibility of developing the cyanide chemistry of the f elements, which has received little attention2–4 in contrast to that of the d transition metals 5. Herein we report on the U III –U V complexes [Cp* 2 U(CN) 3 ][NR 4 ] n ( n =1, 2) and [Cp* 2 U(CN) 5 ][NR 4 ] n ( n =2, 3), which adopt a bent and linear configuration, respectively.…”

Back-bonding between an electron-poor, high-oxidation-state metal and poor π-acceptor ligand in a uranium(v)–dinitrogen complex

“…14,15 For early actinides, outside of cryogenic matrix isolation conditions 2,3 N 2 derivatives tend to be strongly activated and reduced to side-on-bound (N 2 ) nby polymetallic-mediated reductions, [16][17][18][19] or complete cleavage to nitrides occurs. 20,21 Very few isolable, structurally characterised end-on CO, N 2 , or NO actinide complexes are known, [22][23][24][25][26][27][28][29] and all terminal end-on complexes are supported by tris(cyclopentadienyl) ligand sets. [22][23][24][25][27][28][29] The back-bonding in these systems stems not from metal orbitals but cyclopentadienyl ligand orbitals, 30 reminiscent of transition metal analogues, 11 or in the case of NO formal full reduction to (NO) 1occurs, 29 so these are quite different from the classical metal-to-ligand back-bonding model.…”

“…1 Notably, all uranium complexes with end-on CO or N 2 involve electron-rich 5f 3 uranium(III). [22][23][24][25]28 Although 5f orbitals are radially more expanded than 'core-like' 4f orbitals, they only just penetrate the valence region, so such metal-to-ligand interactions and π-acceptor ligand activation is weak, as evidenced by their reversible coordination and dominance of ligand-to-ligand back-bonding. However, it should be noted that even though actinide-metallocenes represent a non-classical case of donor-acceptor bonding, 30 31 In order to establish the fundamental properties of 1 we have examined its reactivity towards a wide range of substrates.…”