A highly reduced cyanogen ligand derived from cyanide reductive coupling.

The synthesis, structure, and spectroscopic features of a bimetallic cyanogen complex obtained from the reductive coupling of cyanide by a niobium(IV) precursor are described, and a mechanism for the coupling reaction is proposed based on DFT calculations.

A bimetallic uranium mu-dicarbide complex: synthesis, X-ray crystal structure, and bonding.

The synthesis, spectroscopy, structure, and bonding of the molecular uranium dicarbide complex (mu,eta(1):eta(1)-C(2))[U(N[t-Bu]Ar)(3)](2) (Ar = 3,5-Me(2)C(6)H(3)) is described.

Uranium-nitrogen multiple bonding: isostructural anionic, neutral, and cationic uranium nitride complexes featuring a linear U=N=U core.

Reaction of the uranium(III) tris(anilide) complex (THF)U(N[t-Bu]Ar)(3) (1, THF = tetrahydrofuran; Ar = 3,5-Me(2)C(6)H(3)) with MN(3) (M = Na, [N(n-Bu)(4)]) results in the formation of the bimetallic diuranium(IV/IV) complexes M[(mu-N)(U(N[t-Bu]Ar)(3))(2)] (M[3]), which feature a single nitride ligand engaged as a linear, symmetric bridge between two uranium centers. The stability of the U=N=U core across multiple charge states is illustrated by stepwise chemical oxidation of Na[3] to the diuranium(IV/V) complex (mu-N)(U(N[t-Bu]Ar)(3))(2) (3) and the diuranium(V/V) complex [(mu-N)(U(N[t-Bu]Ar)(3))(2)][B(Ar(F))(4)] {[3][B(Ar(F))(4)]; Ar(F) = 3,5-(CF(3))(2)C(6)H(3)}. M[3], 3, and [3][B(Ar(F))(4)] were characterized by NMR spectroscopy, single-crystal X-ray diffraction, and elemental analysis. The cyclic voltammogram of 3 reveals two clean, reversible one-electron electrochemical events at E(1/2) = -1.69 and -0.67 V, assigned to the [3](-)/3 and 3/[3](+) redox couples, respectively. The X-ray crystal structures of [N(n-Bu)(4)][3], 3, and [3][B(Ar(F))(4)] reveal a linear U=N=U core that contracts by only approximately 0.03 A across the [3](n) (n = -1, 0, +1) series, an effect that is rationalized as being primarily electrostatic in origin. [3][B(Ar(F))(4)] reacts with NaCN, eliminating Na[B(Ar(F))(4)] and forming the known diuranium(IV/IV) cyanoimide complex (mu-NCN)(U(N[t-Bu]Ar)(3))(2), suggesting that the U=N=U core has metallonitrene-like character.

Uranium-nitrogen multiple bonding: the case of a four-coordinate uranium(VI) nitridoborate complex.

Reaction of the azidoborate salt [N(n-Bu)(4)][(C(6)F(5))(3)B(N(3))] ([N(n-Bu)(4)][1]) with the uranium(III) tris(anilide) complex (THF)U(N[t-Bu]Ar)(3) (2; THF = tetrahydrofuran; Ar = 3,5-Me(2)C(6)H(3)) results in formation of the paramagnetic uranium(V) nitridoborate complex [N(n-Bu)(4)][(C(6)F(5))(3)BNU(N[t-Bu]Ar)(3)] ([N(n-Bu)(4)][3]). Chemical oxidation of [N(n-Bu)(4)][3] is facile and provides the diamagnetic uranium(VI) nitridoborate complex (C(6)F(5))(3)BNU(N[t-Bu]Ar)(3) (3). [N(n-Bu)(4)][3] and 3 are the first nitridoborate complexes of uranium and were characterized by multinuclear NMR spectroscopy, single crystal X-ray diffraction methods, and elemental analysis. The X-ray crystal structures of [N(n-Bu)(4)][3] and 3 reveal extremely short UN(nitrido) distances (1.916(4) A and 1.880(4) A, respectively). Density functional theory was used to calculate the optimized structure of the truncated model (C(6)F(5))(3)BNU(N[Me]Ph)(3); the procedure was carried out similarly for several other relevant complexes featuring UN multiple bonds. Bond multiplicities based on Nalewajski-Mrozek valence indices were calculated, the results of which suggest that the UN(nitrido) interaction in 3 is close to a full triple bond.

Towards uranium catalysts.

The forefront of research into the complexes of uranium reveals chemical transformations that challenge and expand our view of this unique element. Certain ligands form multiple bonds to uranium, and small, inert molecules such as nitrogen and carbon dioxide become reactive when in complex with the metal. Such complexes provide clues to the catalytic future of uranium, in which the applications of the element extend far beyond the nuclear industry. Most excitingly, the ability of uranium to use its outermost f electrons for binding ligands might enable the element to catalyse reactions that are impossible with conventional, transition-metal catalysts.

Solution behavior and structural properties of Cu(I) complexes featuring m-terphenyl isocyanides.

The synthesis of the m-terphenyl isocyanide ligand CNAr (Mes2) (Mes = 2,4,6-Me 3C 6H 2) is described. Isocyanide CNAr (Mes2) readily functions as a sterically encumbering supporting unit for several Cu(I) halide and pseudo halide fragments, fostering in some cases rare structural motifs. Combination of equimolar quantities of CNAr (Mes2) and CuX (X = Cl, Br and I) in tetrahydrofuran (THF) solution results in the formation of the bridging halide complexes (mu-X) 2[Cu(THF)(CNAr (Mes2))] 2. Addition of CNAr (Mes2) to cuprous chloride in a 2:1 molar ratio generates the complex ClCu(CNAr (Mes2)) 2 in a straightforward manner. Single-crystal X-ray diffraction has revealed ClCu(CNAr (Mes2)) 2 to exist as a three-coordinate monomer in the solid state. As determined by solution (1)H NMR and FTIR spectroscopic studies, monomer ClCu(CNAr (Mes2)) 2 resists tight binding of a third CNAr (Mes2) unit, resulting in rapid isocyanide exchange. Contrastingly, addition of 3 equiv of CNAr (Mes2) to cuprous iodide readily affords the tris-isocyanide species, ICu(CNAr (Mes2)) 3, as determined by X-ray diffraction. Similar coordination behavior is observed in the tris-isocyanide salt [(THF)Cu(CNAr (Mes2)) 3]OTf (OTf = O 3SCF 3), which is generated upon treatment of (C 6H 6)[Cu(OTf)] 2 with 6 equiv of CNAr (Mes2) in THF. The disparate coordination behavior of the [CuCl] fragment relative to both [CuI] and [CuOTf] is rationalized in terms of structure and Lewis acidity of the Cu-containing fragments. The putative triflate species [Cu(CNAr (Mes2)) 3]OTf itself serves as a good Lewis acid and is found to weakly bind C 6H 6 in an eta (1)- C manner in the solid-state. Density Functional Theory is used to describe the bonding and energetics of the eta (1)- C Cu-C 6H 6 interaction.