Corresponding complexes have been obtained by reaction of complexes bearing side-on triply-reduced (N2) ligands with electrophiles or proton donors (Figure ), but direct reaction with H2 has not been witnessed to date. Recently, Arnold and co-workers showed that dinuclear Sm and Ce complexes could generate bis-and tris(silyl)amine with a turnover of up to 4 using a large excess of metallic reductant in the presence of excess Me3SiCl or proton sources. Additionally, following seminal reports on photochemical assistance in producing ammonia from N2, 13 the group of Borbas recently reported photocatalytic ammonia formation by a Sm complex bearing a built-in coumarin chromophore. During revision of this article, the group of Peters achieved electrocatalytic N2 reduction to ammonia using a tandem Sm/Mo catalytic system in the presence of proton sources. Historically, the chemistry of divalent lanthanide complexes has been dominated by Sm II , Eu II , and Yb II species, which feature relatively stable 4f n Ln II electronic configurations. The corresponding metallocene chemistry has flourished, especially in the context of single-electron transfer (SET) reductions, typically leading to Ln III end products. 17 Although cyclopentadienyl (Cp) complexes of all the lanthanides, except radioactive Pr, have been isolated in the +II oxidation state, 18 fewer studies have focused on the so-called "non-classical divalent lanthanides", consisting of the remainder of the 4f series. This relative scarcity can be traced back to experimental difficulties in handling these very reactive and reducing species. Among them, Tm II is the most accessible in terms of reduction potential, yet displays strong reducing properties beneficial for molecular activation via SET reactions. 11d,21 In this context, our group recently showed that the Tm II complex [Tm(Cp ttt )2] (Cp ttt = 1,2,4tris(tert-butyl)cyclopentadienyl) displays unique reactivity in terms of CO reductive coupling and subsequent functionalization reactions. The choice of the Cp ttt ligand was crucial to kinetically stabilize the reactive metal center while still allowing the coordination of an exogenous ligand. The three bulky tert-butyl substituents confer high thermal stability but slightly hamper reactivity, as [Tm(Cp ttt )2] does not react with N2, contrary to the less sterically protected analogues. An extreme case of stabilization was recently reported by Long, Harvey and co-workers through the use of the pentasubstituted Cp iPr5 (Cp iPr5 = pentaisopropylcyclopentadienyl) ligand. The redox potential of the corresponding Tm II complex was evaluated as high as -1.57 V, more than 1 V less reducing than other Tm II Cp-type complexes. In the present study, we were interested in investigating whether the Cp ttt ligand would allow the stabilization of even more reducing Lu II complexes. In addition to advantageous properties in terms of quantum applications, Lu II species appear particularly attractive to uncover novel reactivities, especially in terms of small molecule activation via SET reductions. Unlike Tm III species that are strongly paramagnetic, Lu III end products are diamagnetic, allowing precise monitoring of reactions by multinuclear NMR spectroscopy. Surprisingly, only three molecular Lu II complexes have been reported to date (Figure ), the two separated ion-pair complexes [K(crypt)][LuCp '3] (Cp' = C5H4SiMe3) and [K(crypt)][Lu(OAr*)3] (OAr* = 2,6-bis(adamantly)-4-t Bu-C6H2O), and the neutral [Lu(Cp iPr5 )2] complex. 18d In this work, we show how the fluxional behavior of the Cp ttt ligand in [Lu(Cp ttt )2] allows the stabilization of a highly reactive Lu II complex while still offering an open coordination site for original reactivity (Figure ). It is worth noting that, during this work, Evans and co-workers reported the synthesis of the related [Sc(Cp ttt )2] and its coordination chemistry towards CO and isocyanides. Herein, we show that [Lu(Cp ttt )2] induces unprecedented reactivities in lanthanide chemistry, such as direct H2 splitting and N2 hydrogenation under very smooth conditions (Figure ).