Calcium catches dinitrogen: Although lithium reduces dinitrogen, the other alkali and alkaline Earth metals have proven largely inert to the gas under ambient conditions. Rösch et al. report that with just the right β-diketiminate ligand and an assist from potassium as terminal reductant, calcium can mediate dinitrogen reduction. Crystallography and spectroscopic characterization revealed a product in which doubly reduced dinitrogen adopted a side-on bridging motif between two calcium centers. A subsequent reaction with coordinated tetrahydrofuran appeared to release diazene. Science , this issue p. 1125

The reagent RK [R=CH(SiMe₃)₂ or N(SiMe₃)₂] was expected to react with the low‐valent (^DIPPBDI)Al (^DIPPBDI=HC[C(Me)N(DIPP)]₂, DIPP=2,6‐iPr‐phenyl) to give [(^DIPPBDI)AlR]⁻K⁺. However, deprotonation of the Me group in the ligand backbone was observed and [H₂C=C(N‐DIPP)−C(H)=C(Me)−N−DIPP]Al⁻K⁺ (1) crystallized as a bright‐yellow product (73 %). Like most anionic Al^I complexes, 1 forms a dimer in which formally negatively charged Al centers are bridged by K⁺ ions, showing strong K⁺⋅⋅⋅DIPP interactions. The rather short Al–K bonds [3.499(1)–3.588(1) Å] indicate tight bonding of the dimer. According to DOSY NMR analysis, 1 is dimeric in C₆H₆ and monomeric in THF, but slowly reacts with both solvents. In reaction with C₆H₆, two C−H bond activations are observed and a product with a para‐phenylene moiety was exclusively isolated. DFT calculations confirm that the Al center in 1 is more reactive than that in (^DIPPBDI)Al. Calculations show that both Al^I and K⁺ work in concert and determines the reactivity of 1.