Expanding Dinitrogen Reduction Chemistry to Trivalent Lanthanides via the LnZ₃/Alkali Metal Reduction System: Evaluation of the Generality of Forming Ln₂(μ<i>-</i>η<i>²</i><i>:</i>η<i>²</i>-N₂) Complexes via LnZ₃/K

The Ln[N(SiMe3)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(SiMe3)2]3/K reduction of dinitrogen provides access from readily available starting materials to the formerly rare class of M2(μ-η2:η2-N2) complexes, {[(Me3Si)2N]2(THF)Ln}2(μ-η2:η2-N2), 1, that had previously been made only from TmI2, DyI2, and NdI2 in the presence of KN(SiMe3)2. This LnZ3/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) Å range consistent with formation of an (NN)2- moiety. Isolation of 1 with this selection of metals demonstrates that the Ln[N(SiMe3)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(SiMe3)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(SiMe3)2]4}-, are isolated as THF-solvated potassium or sodium salts. The implications of the LnZ3/alkali metal reduction chemistry on the mechanism of dinitrogen reduction and on reductive lanthanide chemistry in general are discussed.本研究针对模拟高还原性二价离子Tm(II)、Dy(II)与Nd(II)反应的Ln[N(SiMe3)2]3/钾二氮还原体系，对全部镧系元素及铀开展了系统探索，旨在验证该体系的普适性，并将观测到的反应活性与二价氧化态的可及性相关联。Ln[N(SiMe3)2]3/钾介导的二氮还原反应，可从易得起始原料出发，制备此前仅能通过TmI2、DyI2和NdI2在KN(SiMe3)2存在下合成的稀有双核μ-η2:η2桥联二氮配合物{[(Me3Si)2N]2(THF)Ln}2(μ-η2:η2-N2)（记为化合物1）。该LnZ3/碱金属还原体系可针对Nd、Gd、Tb、Dy、Ho、Er、Y、Tm及Lu获得可经晶体学表征的化合物1实例。碱金属除钾外，也可使用钠。此类化合物的N-N键长介于1.258(3)~1.318(5) Å范围内，与(N=N)²⁻物种的形成相符。通过对上述金属的筛选分离得到化合物1，证明Ln[N(SiMe3)2]3/碱金属反应可模拟二价镧系还原化学，适配的金属其计算得到的Ln(III)/Ln(II)还原电势相对于标准氢电极(NHE)介于-2.3 V至-3.9 V之间。对于Ln为钐(Sm)的情况，其Ln(III)/Ln(II)电势为-1.55 V，反应仅生成稳定的二价三酰胺配合物K{Sm[N(SiMe3)2]3}，并未发生二氮还原。当金属为La、Ce、Pr或铀时，可分离得到首例可经晶体学表征的四[双(三甲基硅基)酰胺(bis(trimethylsilyl)amide)]阴离子{ M[N(SiMe3)2]4 }⁻的溶剂化四氢呋喃(THF)钾盐或钠盐。本文还讨论了LnZ3/碱金属还原化学对二氮还原机理及通用还原镧系化学的启示。