Expanding Dinitrogen Reduction Chemistry to Trivalent Lanthanides via the LnZ₃/Alkali Metal Reduction System:  Evaluation of the Generality of Forming Ln₂(μ-η²:η²-N₂) Complexes via LnZ₃/K

Abstract

The Ln[N(SiMe(3))(2)](3)/K dinitrogen reduction system, which mimicks the reactions of the highly reducing divalent ions Tm(II), Dy(II), and Nd(II), has been explored with the entire lanthanide series and uranium to examine its generality and to correlate the observed reactivity with accessibility of divalent oxidation states. The Ln[N(SiMe(3))(2)](3)/K reduction of dinitrogen provides access from readily available starting materials to the formerly rare class of M(2)(mu-eta(2):eta(2)-N(2)) complexes, [[(Me(3)Si)(2)N](2)(THF)Ln](2)(mu-eta(2):eta(2)-N(2)), 1, that had previously been made only from TmI(2), DyI(2), and NdI(2) in the presence of KN(SiMe(3))(2). This LnZ(3)/alkali metal reduction system provides crystallographically characterizable examples of 1 for Nd, Gd, Tb, Dy, Ho, Er, Y, Tm, and Lu. Sodium can be used as the alkali metal as well as potassium. These compounds have NN distances in the 1.258(3) to 1.318(5) A range consistent with formation of an (N=N)(2)(-) moiety. Isolation of 1 with this selection of metals demonstrates that the Ln[N(SiMe(3))(2)](3)/alkali metal reaction can mimic divalent lanthanide reduction chemistry with metals that have calculated Ln(III)/Ln(II) reduction potentials ranging from -2.3 to -3.9 V vs NHE. In the case of Ln = Sm, which has an analogous Ln(III)/Ln(II) potential of -1.55 V, reduction to the stable divalent tris(amide) complex, K[Sm[N(SiMe(3))(2)](3)], is observed instead of dinitrogen reduction. When the metal is La, Ce, Pr, or U, the first crystallographically characterized examples of the tetrakis[bis(trimethylsilyl)amide] anions, [M[N(SiMe(3))(2)](4)](-), are isolated as THF-solvated potassium or sodium salts. The implications of the LnZ(3)/alkali metal reduction chemistry on the mechanism of dinitrogen reduction and on reductive lanthanide chemistry in general are discussed.

Advances in f element reductive reactivity as a paradigm for expanding lanthanide and actinide science and technology

“…(46) was successful with most of the lanthanides, crystals of {[(Me 3 Si) 2 N] 2 Ln} 2 ( -Á 2 :Á 2 -N 2 ) products were not obtainable for Ln = La, Ce, and Pr [102]. Examination of Table 4 shows that this does not correlate with calculated reduction potentials, i.e.…”

“…In efforts to find alternative routes to these reactive "LnZ 2 " intermediates, the reduction of Ln[N(SiMe 3 ) 2 ] 3 with potassium metal was investigated [101,102]. Bradley showed in the 1970s that these Ln[N(SiMe 3 ) 2 ] 3 complexes can be readily synthesized from LnCl 3 and [N(SiMe 3 ) 2 ] 1− salts [103].…”

Beyond Samarium Diiodide: Vistas in Reductive Chemistry Mediated by Lanthanides(II)

“…[108] Finally, while investigating dinitrogen activation using nonclassical lanthanides (Tm, Dy and Nd), Evans et al reported an intriguing approach to other divalent lanthanides by the in situ reduction of their three-valent precursors. [109] In particular, dinitrogen activation occurred when lanthanide-(III) amides, [Ln(hmds) 3 ], were reacted with alkali metals, thus indicating the transient presence of divalent lanthanide intermediates. Remarkably, this reaction sequence proved successful with Tm, Nd, Dy, Ho, Er, Tb, Gd, Y, and Lu.…”

Rare earth metal bis(alkyl) complexes bearing a monodentate arylamido ancillary ligand: Synthesis, structure, and Olefin polymerization catalysis

“…Both Gd atoms form a distorted trigonal prism geometry. The average bond lengths of Gd-N (2.301 (3) [20]. The Gd-C bond lengths in 5 range broadly from 2.471(4) Å to 2.757(4) Å , in which the shortest Gd-C bond distance (2.471(4) Å ) is similar to that of the terminal Gd-benzyl bond in (C 5 Me 5 )Gd(CH 2 C 6 H 5 ) 2 (thf) (2.470(7) Å ) [21].…”