N-Containing organic compounds are of vital importance to lives. Practical synthesis of valuable N-containing organic compounds directly from dinitrogen (N2), not through ammonia (NH3), is a holy-grail in chemistry and chemical industry. An essential step for this transformation is the functionalization of the activated N2 units/ligands to generate N−C bonds. Pioneering works of transition-metal mediated direct conversion of N2 into organic compounds via N−C bond formation at metal dinitrogen [N2-M] complexes have generated diversified coordination modes and laid the foundation of understanding for N−C bond formation mechanism. This review summarizes those major achievements and is organized by the coordination modes of the [N2-M] complexes (end-on, side-on, end-on-side-on, etc.) that are involved in the N−C bond formation steps, and each part is arranged in terms of reaction types (N-alkylation, N-acylation, cycloaddition, insertion, etc.) between [N2-M] complexes and carbon-based substrates. Besides, earlier works on one-pot synthesis of organic compounds from N2 via ill-defined intermediates are also briefed. Although almost all of the syntheses of N-containing organic compounds via direct transformation of N2 so far in the literature are realized in homogeneous stoichiometric thermochemical reaction systems and are discussed here in detail, the sporadically reported syntheses involving photochemical, electrochemical, heterogeneous thermo-catalytic reactions, if any, are also mentioned. This review aims to provide readers with in-depth understanding of the state-of-the-arts and perspectives of future research particularly in direct catalytic and efficient conversion of N2 into N-containing organic compounds under mild conditions, and to stimulate more research efforts to tackle this longstanding and grand scientific challenge.

Direct conversion of dinitrogen (N 2 ) into organic compounds, not through ammonia (NH 3 ), is of great significance both fundamentally and practically.Here we report a highly efficient scandium-mediated synthetic cycle affording hydrazine derivatives (RMeN− NMeR′) directly from N 2 and carbon-based electrophiles. The cycle includes three main steps: (i) reduction of a halogen-bridged discandium complex under N 2 leading to a (N 2 ) 3− -bridged discandium complex via a (N 2 ) 2− intermediate; (ii) treatment of the (N 2 ) 3− complex with methyl triflate (MeOTf), affording a (N 2 Me 2 ) 2− -bridged discandium complex; and (iii) further reaction of the (N 2 Me 2 ) 2− complex with the carbon-based electrophile, producing the hydrazine derivative and regenerating the halide precursor. Furthermore, insertion of a CO molecule into one Sc−N bond in the (N 2 Me 2 ) 2− −scandium complex was observed. Most notably, this is the first example of rare-earth metal-promoted direct conversion of N 2 to organic compounds; the formation of C−N bonds by the reaction of these (N 2 ) 3− and (N 2 Me 2 ) 2− complexes with electrophiles represents the first case among all N 2 − metal complexes reported.

Exploring new lanthanide metallacycles and finding their unique chemistry different from the analogues of transition metals are of great interest and importance. In this work, we reported the synthesis, characterization, and reactivity toward nitriles of two lanthanide metallacyclopropenes: lutetacyclopropene 2a and dysprosacyclopropene 2b. The selective coupling of 2a and three molecules of PhCN was found for the first time to provide the unexpected fused lutetacycle 3a with one 1,6-dihydropyrimidine ring. Mechanistic studies by DFT calculations reveal that the triple insertion of PhCN into 2a proceeds through four key steps: the insertion of the first PhCN into 2a giving azalutetacyclopentadiene IM1, the insertion of the second PhCN into the Lu–N bond of IM1, the intramolecular electrocyclization providing a highly strained η2-pyrimidine metallacycle, and the insertion of the third PhCN into the Lu–Csp3 bond. Isolation and characterization of two active intermediates, azalutetacyclopentadiene IM1 and η2-pyrimidine dysprosacycle, provide critical evidence for the formation of 3a. Furthermore, IM1 was also reported to react with TMSCN, isocyanides, or W­(CO)6 to furnish the fused [4,5] lutetacycles. The chemistry of two lanthanide metallacyclopropenes with nitriles is significantly different from these metallacyclopropenes of scandium and other metals. Most notably, the azalutetacyclopentadienes, η2-pyrimidine complex, and other metallacycles all represent the first examples in rare-earth organometallic chemistry; the formation of these new lutetacycles provides concrete evidence for understanding the mechanism of transition metal promoted or catalyzed [2+2+2] cycloaddition between alkynes and nitriles.