Search

Out of the 14 lanthanide (Ln) ions, molecular complexes of Ln(IV) were known only for cerium and more recently terbium. Here we demonstrate that the +IV oxidation state is also accessible for the large praseodymium (Pr) cation. The oxidation of the tetrakis(triphenysiloxide) Pr(III) ate complex, [KPr(OSiPh3)(4)(THF)(3)], 1-Pr-Ph, with [N(C6H4Br)(3)][SbCl6], affords the Pr(IV) complex [Pr(OSiPh3)(4)(MeCN)(2)], 2-Pr-Ph, which is stable once isolated. The solid state structure, UV-visible spectroscopy, magnetometry, and cyclic voltammetry data along with the DFT computations of the 2-Pr-Ph complex unambiguously confirm the presence of Pr(IV).

Synthetic studies of bimetallic uranium nitride complexes with the N(SiMe3)2 ligand have generated a new nitride complex of U(III), which is highly reactive toward C-H bonds and H2. Treatment of the previously reported U(IV)/U(IV) nitride complex [Na(DME)3][((Me3Si)2N)2U(μ-N)(μ-κ2:CN-CH2SiMe2NSiMe3)U(N(SiMe3)2)2] (DME = 1,2-dimethoxyethane), 1, with 2 equiv of HNEt3BPh3 yielded the cationic U(IV)/U(IV) nitride complex, [{((Me3Si)2N)2U(THF)}2(μ-N)][BPh4] (THF = tetrahydrofuran), 3, by successive protonolysis of one N(SiMe3)2 ligand and the uranium-methylene bond. Reduction of 3 with KC8 afforded a rare example of a U(III) nitride, namely, the U(III)/U(IV) complex, [{((Me3Si)2N)2U(THF)}2(μ-N)], 4. Complex 4 is highly reactive and undergoes 1,2-addition of the C-H bond of the N(SiMe3)2 ligand across the uranium-nitride moiety to give the U(III)/U(IV) imide cyclometalate complex, [((Me3Si)2N)2(THF)U(μ-NH)(μ-κ2:C,N-CH2SiMe2NSiMe3)U(N(SiMe3)2))(THF)], 5. Complex 4 also reacts with toluene at -80 °C to yield an inverse sandwich imide complex arising from C-H bond activation of toluene, [{((Me3Si)2N)2U(THF)}2(μ-N)][{((Me3Si)2N)3U(μ-NH)U(N(SiMe3)2)}2(C7H8)], 6. Complex 4 effects the heterolytic cleavage of the C-H of phenylacetylene to yield the imide acetylide [{((Me3Si)2N)2U(THF)}2(μ-N)][((Me3Si)2N)2U(η1-CCPh)(μ2-NH)(μ2-η2:η1-CCPh)U(N(SiMe3)2)2], 7. Complex 4 also reacts with H2 to produce an imide hydride U(III)/U(IV) complex, [{((Me3Si)2N)2U(THF)}2(μ-NH)(μ-H)], 9. These data demonstrate that nitride complexes of U(III) are accessible with amide ligands and show the high reactivity of molecular U(III) nitrides in C-H bond activation.

Electrocatalytic energy conversion with molecular f-element catalysts is still in an early phase of its development. We here report detailed electrochemical investigations on the recently reported trivalent lanthanide coordination complexes [((Ad,MeArO)3mes)Ln] (1–Ln), with Ln = La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and Yb, which were now found to perform as active electrocatalysts for the reduction of water to dihydrogen. Reactivity studies involving complexes 1–Ln and the Ln(II) analogues [K(2.2.2-crypt)][((Ad,MeArO)3mes)Ln] (2–Ln) suggest a reaction mechanism that differs significantly from the reaction pathway found for the corresponding uranium catalyst [((Ad,MeArO)3mes)U] (1–U). While complexes 1−Ln activate water via a radical pathway, only upon a 1 e− reduction to yield the reduced species 2−Ln, the 5f analogue 1−U directly reduces H2O via a 2 e− pathway. The electrocatalytic H2O reduction by complexes 1–Ln is initiated by the respective Ln(III)/Ln(II) redox couples, which gradually turn to more positiv...

Electrocatalytic energy conversion with molecular f-element catalysts is still in an early phase of its development. We here report detailed electrochemical investigations on the recently reported trivalent lanthanide coordination complexes [((