Beyond Ammonia: Nitrogen–Element Bond Forming Reactions with Coordinated Dinitrogen

Abstract

The functionalization of coordinated dinitrogen to form nitrogen–element bonds en route to nitrogen-containing molecules is a long-standing challenge in chemical synthesis. The strong triple bond and the nonpolarity of the N2 molecule pose thermodynamic and kinetic challenges for promoting reactivity. While heterogeneous, homogeneous, and biological catalysts are all known for catalytic nitrogen fixation to ammonia, the catalytic synthesis of more complicated nitrogen-containing organic molecules has far less precedent. The example of silyl radical additions to coordinated nitrogen to form silylamines stands as the lone example of a catalytic reaction involving N2 to form a product other than ammonia. This Review surveys the field of molecular transition metal complexes as well as recent boron examples for the formation of nitrogen–element bonds. Emphasis is placed on the coordination and activation modes of N2 in the various metal compounds from across the transition series and how these structures can rationally inform reactivity studies. Over the past few decades, the field has evolved from the addition of carbon electrophiles in a manner similar to that of protonation reactions to more organometallic-inspired reactivity, including insertions, 1,2-additions, and cycloadditions. Various N–C, N–Si, and N–B bond-forming reactions have been discovered, highlighting that the challenge for catalytic chemistry is not in the reactivity of coordinated dinitrogen but rather removal of the functionalized ligand from the coordination sphere of the metal.

Dinitrogen Fixation: Rationalizing Strategies Utilizing Molecular Complexes

“…By providing a straightforward understanding of the reaction mechanisms and by allowing for the fine management of electron and proton transfer steps via the tuning of the active sites properties, molecular complexes have shown a strong potential to promote catalytic nitrogen reduction under mild conditions [12, 14, 15] . To date, dinitrogen metal complexes have been isolated with almost all metals from first to third row to rare‐earth metals, [16, 17] but very few have led to the stoichiometric functionalization of dinitrogen and only a handful have been reported to enable catalytic functionalization [18–20] . Although recent reviews have surveyed dinitrogen activation by polynuclear complexes, [20] bond‐forming reactions from activated dinitrogen [19] and catalytic dinitrogen to ammonia formation using molecular complexes, [15] this Review will explore a complementary approach, encompassing aspects from all these reviews.…”

“…To date, dinitrogen metal complexes have been isolated with almost all metals from first to third row to rare‐earth metals, [16, 17] but very few have led to the stoichiometric functionalization of dinitrogen and only a handful have been reported to enable catalytic functionalization [18–20] . Although recent reviews have surveyed dinitrogen activation by polynuclear complexes, [20] bond‐forming reactions from activated dinitrogen [19] and catalytic dinitrogen to ammonia formation using molecular complexes, [15] this Review will explore a complementary approach, encompassing aspects from all these reviews. We aim to provide an overview of the successful strategies utilizing molecular complexes to promote nitrogen reduction and functionalization with H, C and Si sources under mild conditions according to their proposed reaction mechanisms.…”

“…Other bond‐forming reactions with elements such as boron, phosphorous or with other Lewis acids are excluded from the scope of the current Review as their scarcity complicates the possibility to draw mechanistic conclusions. The interested reader may refer to the recent reviews from Chirik and co‐workers [19] and Simmoneau and Etienne, [21] which provide a good overview on the recent research in the field.…”

Facile Dinitrogen and Dioxygen Cleavage by a Uranium(III) Complex: Cooperativity Between the Non‐Innocent Ligand and the Uranium Center

“…[1][2][3][4][5] Since the first N 2 complex of at ransition metal was reported in 1965, [6] chemists endeavor to explore molecular systems which can be utilized for fixation and activation of N 2 under mild conditions. [7][8][9][10][11][12][13][14] In the past few decades,aseries of significant advances in the N 2 fixation and activation have been demonstrated by transition metal complexes [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] as well as by organoboron species. [31][32][33][34][35] In addition, molecular uranium systems also exhibit attractive ability for N 2 binding,r eduction, and activation.…”

“…The activation and cleavage of dinitrogen (N 2 ) remains a challenge due to its inert N≡N triple bond [1–5] . Since the first N 2 complex of a transition metal was reported in 1965, [6] chemists endeavor to explore molecular systems which can be utilized for fixation and activation of N 2 under mild conditions [7–14] . In the past few decades, a series of significant advances in the N 2 fixation and activation have been demonstrated by transition metal complexes [15–30] as well as by organoboron species [31–35] .…”