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A quintessential approach to activate and functionalize the exceptionally stable diatomic nitrogen (N2) consists of its coordination to transition metal complexes.

Cobalt-bis(dinitrogen) complexes [LCo(N2)2]− (3,4) with simple and commercially available bidentate phosphine ligands (L: Cy2PCH2CH2PCy2) were synthesized and structurally characterized. Further N2...

The reaction of Bppy(Mes)2 (BN1; ppy = 2-phenylpyridine) and BCH2ppy(Mes)2 (BN3) with the reducing reagent resulted in the 4,4′bipyridyl liganded neutral, anionic, and dianionic compounds.

The reduction of PNPCoBr under a N2 atmosphere yielded a binuclear cobalt dinitrogen anion complex via the C–P bond cleavage of the PNP ligand.

A series of structurally well-defined iron–dinitrogen complexes (LFe–N2) bearing cyclopentadienyl-phosphine ligands (L) were synthesized and analyzed by single-crystal X-ray structural analysis, IR...

Rare-earth metal boroxides are not only rare and of great synthetic challenge but also important theoretically due to their unrevealed bonding characteristics. In this paper, we report the synthesi...

By applying the potassium salts of cyclopentadienyl-phosphine ligands LK to CoCl

The element nitrogen and nitrogenous compounds are vital to life. The synthesis of nitrogen-containing compounds using dinitrogen as the nitrogen source, not through ammonia, is of great interest and great value but remains a grand challenge. Herein, we describe a strategy to realize this transformation by combining the heterogeneous approach with the homogeneous methodology. The N2 molecule was first fixed with carbon and LiH through a one-pot heterogeneous process, forming Li2CN2 as an ‘activated’ nitrogen source with high efficiency. Then subsequent homogeneous treatments of Li2CN2 to construct the organic synthon carbodiimide and the RNA/DNA building block pyrimidines were fulfilled. By using 15N2 as the feedstock, their corresponding 15N-labeled carbodiimide and pyrimidines were readily obtained. This homogeneous–heterogeneous synergy strategy will open a new chapter for N2 transformation.

Reactions of [PhC(NtBu)2]ECl (E = Si, Ge) with Li[(3,5-Me2-C6H3)NPiPr2] afforded the mixed donor ligands [PhC(NtBu)2]E[(3,5-Me2-C6H3)NPiPr2] (1, E = Si; 2, E = Ge) in high yields. Further reaction ...

New kinds of diradical rare-earth metal complexes supported by diazabutadiene (DAD) ligands, [(DAD)2LnN(TMS)2] (1; Ln = Dy, Lu; TMS = SiMe3), were synthesized and studied. They showed a new [radical-Ln-radical] alignment with distorted square-pyramidal geometry. Structural and density functional theory analysis illustrated the radical anionic nature of the ligands. Magnetic studies revealed antiferromagnetic coupling of the two radicals in 1-Lu. 1-Dy showed typical single-molecule-magnet (SMM) behavior with an effective energy barrier of 231 K, which is much higher than those of similar radical-containing SMMs. Magnetostructural analysis suggests that the anionic [N(TMS)2]- group plays a vital role in the SMM property. This study provides a new platform for further improving the performance of radical-Ln SMMs.

Synthesis and structural characterization of inverse-sandwich complexes, whose planar conjugated ligand is a cyclobutadiene, have attracted much attention for their unique chemical bonding modes an...

A new class of nonplanar metalla-aromatics, diiron complexes bridged by a 1,3-butadienyl dianionic ligand, were synthesized in high yields from dilithio reagents and two equivalents of FeBr2 . The complexes consist of two antiferromagnetically coupled high-spin FeII centers, as revealed by magnetometry, Mossbauer spectroscopy, and DFT calculations. Furthermore, experimental (X-ray structural analysis) and theoretical analyses (NICS, ICSS, AICD, MOs) suggest that the complexes are aromatic. Remarkably, this nonplanar metalla-aromaticity is achieved by an uncommon σ-type overlap between the ligand p and metal d orbitals, in sharp contrast to the intensively studied planar aromatic systems featuring delocalized π-type bonding. Specifically, the σ-type interaction between the two Fe 3dxz orbitals and the butadienyl π orbital results in the formation of a six-electron conjugated system and hence enables the aromatic character.

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 the 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. Additionally, 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 an in-depth understanding of the state-of-the-art 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 long-standing and grand scientific challenge., This review provides summary and perspectives on direct functionalization/transformation of dinitrogen into N-containing organic compounds, via homogeneous, heterogeneous, thermochemical, photochemical, electrochemical, and other available reaction systems.

An unprecedented class of organo-dimetallic compounds, mono-titanium (Ti/Li) and bis-titanium (Ti/Ti) complexes bridged by 2-butene tetraanionic ligands, were obtained from the reaction of dilithio...

Carbodiimides are a unique class of heterocumulene compounds that display distinctive chemical properties. The rich chemistry of carbodiimides has drawn increasing attention from chemists in recent years and has made them exceedingly useful compounds in modern organic chemistry, especially in the synthesis of N-heterocycles. This review has outlined the extensive application of carbodiimides in the synthesis of N-heterocycles from the 1980s to today. A wide range of reactions for the synthesis of various types of N-heterocyclic systems (three-, four-, five-, six-, seven-, larger-membered and fused heterocycles) have been developed on the basis of carbodiimides and their derivatives.

As key components of air, nitrogen (N2) and oxygen (O2) are the vital constituents of lives. Synthesis of NO2, and C–N–O organics direct from N2 and O2, rather than from an intermediate NH3 (known as the Haber–Bosch process), is tantalizing. However, the extremely strong N≡N triple bond (945 kJ mol–1) and the nonpolar stable electron configuration of dinitrogen lead to its conversion being extensively energy demanding. The further selective synthesis of high-value C–N–O organics directly from N2, O2 and C-containing molecules is attractive yet greatly challenging from both scientific and engineering perspectives. Enormous efforts have been dedicated to the direct conversion of N2 and O2 via traditional and novel techniques, including thermochemical, plasma, electrochemical, ultrasonic and photochemical conversion. In this review, we aim to provide a thorough comprehension of the status and challenge of the direct conversion of N2, O2 and C-containing molecules (particularly N2 and O2). Moreover, we will propose some future perspectives to stimulate more inspiration from the scientific community to tackle the scientific and engineering challenges.

Herein we report the synthesis and applications of unusual trisyl-based multidentate ligands [trisyl = tris(trimethylsilyl)methyl, –C(SiMe3)3].

The reaction chemistry of metalla-aromatics is fundamentally interesting. In this work, we find that tetralithio spiroaromatic palladole and platinacycle complexes 1 undergo selective two-electron ...

Direct conversion of dinitrogen (N2) into organic compounds, not through ammonia (NH3), is of great significance both fundamentally and practically. Here we report a highly efficient scandium-media...

A series of trinuclear and dinuclear Cr(I)–N2 complexes bearing cyclopentadienyl-phosphine ligands were synthesized and characterized. Further reduction of the Cr(I)–N2 complexes generated anionic ...

A series of manganese(II) complexes supported by cyclopentadienyl-phosphine ligands have been synthesized and characterized. A reaction of potassium salts of a cyclopentadienyl-phosphine ligand (LK) with MnX2 provided dimeric complexes [LMn(μ-X)]2 (X = Cl, 1a; X = Br, 1b) in high yields. The monomeric complex [K(18-crown-6)][LMnCl2] (2) was obtained with the addition of 18-crown-6. [LMn(μ-Cl)]2 (1a) served as a precursor to dimeric amido and methyl manganese(II) complexes including [LMn(μ-NH2)]2 (3) and [LMn(μ-Me)]2 (4). Treatment of [LMn(μ-Cl)]2 (1a) with EtMgCl, PhMgBr or other reductants resulted in the formation of sandwich manganese(II) complex L2Mn (5). Complexes 1a,b, 2–5 were characterized by a single-crystal X-ray structural analysis.

ConspectusThe concept of aromaticity is one of the most fundamental principles in chemistry. It is generally accepted that planarity is a prerequisite for aromaticity, and typically the more planar the geometry of an aromatic compound is, the stronger aromatic it is. However, it is not always the case, particularly when transition metals are involved in conjugation and electron delocalization of aromatic systems, i.e., metalla-aromatics. Because of the intrinsic nature of transition-metal orbitals, besides planar geometries, the most stable molecular structures of metalla-aromatic compounds could take nonplanar and even spiro geometries. In this Account, we outline several unprecedented types of metalla-aromatics developed recently in our research group.Around seven years ago, we found that 1,4-dilithio-1,3-butadienes, dilithio reagents with π-conjugation, could function as non-innocent ligands and react with low-valent transition-metal complexes, generating monocyclic metalla-aromatic compounds. Later on, by taking advantage of the unique behavior of dilithio reagents and the intrinsic nature of different transition metals, we have synthesized a series of metalla-aromatic compounds, of which four types are discussed here, and each of them represents the first of its kind. First, nearly planar aromatic dicupra[10]annulenes, a 10 π-electron aromatic system with two bridging Cu atoms participating in the orbital conjugation and electron delocalization, are synthesized by annulating two dilithio reagents with two Cu(I) complexes.Second, four kinds of spiro metalla-aromatics, featuring planar (with Pd, Pt, or Rh as the spiro atom) geometry with a whole 10π aromatic system, octahedral (tris-spiro metalla-aromatics with V as the spiro atom) geometry with an entire 40π Craig-Mobius aromatic system, tetrahedral (with Mn as the spiro atom) geometry having two independent and perpendicular 6π planar aromatic rings, and tetrahedral (with Mn as the spiro atom) geometry with one planar and one nonplanar 6π aromatic rings, respectively, are generated. In sharp contrast to spiroaromaticity with carbon acting as the spiro atom described in Organic Chemistry, the metal spiro atom herein takes part in orbital conjugation and electron delocalization.Third, nonplanar aromatic butadienyl diiron complexes are realized. Different from planar aromatic systems featuring delocalized π-type overlap, this nonplanar metalla-aromaticity is achieved by the novel σ-type overlap between the two Fe 3dxz orbitals and the butadienyl π orbital, forming a 6π aromatic system. Fourth, dinickelaferrocene, a ferrocene analogue with two aromatic nickeloles, is synthesized from our monocyclic aromatic dilithionickelole and FeBr2. The aromaticity of dinickelaferrocene and its nickelole ligands is realized by electron back-donation from the Fe 3d orbital to the π* orbital of nickeloles, which also deepens our understanding of the origin of aromaticity.The search for unprecedented and exciting aromatic systems, particularly with transition metals being involved, will continue to drive this intriguing research field forward. Given the synthetic strategies and various types of metalla-aromatics developed and described, diversified metalla-aromatics of interesting structures and reaction chemistry, novel chemical bonding modes, and useful functions can be expected.

As aromaticity is one of the most fundamental concepts in chemistry, the construction of aromatic systems has long been an important subject. Herein, we report the synthesis and characterization of a tris-spiroaromatic complex, hexalithio spiro vanadacycle 2. The delocalization of the four electrons within the two V 3d orbitals and the π* orbitals of the three biphenyl ligands leads to a 40π Craig-Möbius aromatic system with three metalla-aromatic rings, as revealed by both experimental measurements and theoretical analyses. For comparison, if Cr is used instead of V, a similar Craig-Möbius aromatic system can not be generated. In this case, pentalithio spiro chromacycle 3 is obtained, and the Cr center uses its two 3d orbitals to form two independent metalla-aromatic rings. This work presents a type of aromatic systems that will contribute to both aromaticity theory and organometallic chemistry., Spiroaromatic compounds are advantageous platforms for designing expanded aromatic systems. Herein, the authors present a tris‐spiro metalla‐aromatic Vanadium compound which forms a 40π Craig‐Möbius aromatic system.

Transition-metal alkylidenes have exhibited wide applications in organometallic chemistry and synthetic organic chemistry, however, cyclic Schrock-carbene-like bis-alkylidenes of group 4 metals with a four-electron donor from an alkylidene have not been reported. Herein, the synthesis and characterization of five-membered cyclic bis-alkylidenes of titanium (4 a,b) and zirconium (5 a,b) are reported, as the first well-defined group 4 metallacyclopentatrienes, by two-electron reduction of their corresponding titana- and zirconacyclopentadienes. DFT analyses of 4 a show a four-electron donor (σ-donation and π-donation) from an alkylidene carbon to the metal center. The reaction of 4 a with N,N'-diisopropylcarbodiimide (DIC) leads to the [2+2]-cycloaddition product 6. Compound 4 a reacted with CO, affording the oxycyclopentadienyl titanium complex 7. These reactivities demonstrate the multiple metal-carbon bond character. The reactions of 4 a or 5 a with cyclooctatetraene (COT) or azobenzene afforded sandwich titanium complex 8 or diphenylhydrazine-coordinated zirconacyclopentadiene 9, respectively, which exhibit two-electron reductive ability.

While reduction reactions are ubiquitous in chemistry, it is very challenging to further reduce electron-rich compounds, especially the anionic ones. In this work, the reduction of 1,3-butadienyl dianion, the anionic conjugated olefin, has been realized by divalent rare-earth metal compounds (SmI2), resulting in the formation of novel 2-butene tetraanion bridged disamarium(III) complexes. Density functional theory (DFT) analyses reveal two features: (i) the single electron transfer (SET) from 4f atomic orbitals (AOs) of each Sm center to the antibonding π*-orbitals of 1,3-butadienyl dianion is feasible and the new HOMO formed by the bonding interaction between Sm 5d orbitals (AOs) and the π*-orbitals of 1,3-butadienyl dianion can accept favorably 2e- from 4f AOs of Sm(II); (ii) the 2-butene tetraanionic ligand serves as a unique 10e- donating system, in which 4e- act as two σ-donation bonding interactions while the rest 6e- as three π-donation bonding interactions. The disamarium(III) complexes represent a unique class of the bridged bis-alkylidene rare-earth organometallic complexes. The ligand-based reductive reactivity of 2-butene tetraanion bridged disamarium(III) complexes demonstrates that 2-butene tetraanionic ligand serves as a 3e- reductant toward cyclooctatetraene (COT) to provide doubly COT-supported disamarabutadiene complexes. The reaction of the disamarium(III) complexes with Cp*Li produces the doubly Cp*-coordinated Sm(III) complexes via salt metathesis. In addition, the reaction with Mo(CO)6 affords the oxycyclopentadienyl dinuclear complex via CO insertion.

Development of synthetic methods for silole-containing or –fused polycyclic aromatic compounds has been in great demand. Described in this paper is an easy synthetic method for the high-efficient synthesis of chrysenosilole derivatives from silatricyclic compounds via the Mallory photocyclization reaction. It is noteworthy that those conventional transition-metal and Lewis acid catalyzed or mediated C C bond coupling reactions did not work well for this aryl-aryl coupling reaction.

Synthesis and structural study of cyclobutadiene sandwich transition metal complexes have been an interesting research area, because the cyclobutadiene, a well-recognized unstable anti-aromatic molecule, can be stabilized by coordination with a transition metal, forming stable cyclobutadiene sandwich complexes. Herein, we report the synthesis and structural characterization of novel cyclobutadiene sandwich transition metal complexes, including a cyclobutadiene/toluene iron complex 2, two cyclobutadiene/ferracyclopentadiene iron complexes 3, and a bis(cyclobutadiene) nickel complex 4. These complexes, structurally determined by single-crystal X-ray structural analysis, were all readily obtained from their corresponding metal halides and 1,4-dilithio-1,3-butadienes 1.

Studies on the aggregation states of phospholyl lithiums are of great importance and demand due to their applications as ligands in coordination chemistry. In this paper, we report that the solid-state structures of phospholyl lithiums with different substituents (2a,b, R1 = Ph, R2 = TMS; 3a,b, R1 = Me, R2 = TMS; 4, R1 = R2 = Et) could be in the form of a monomer, dimer, and coordination polymer, respectively. These phospholyl lithiums can change to monomeric structures (5, R1 = Ph, R2 = TMS; 6, R1 = Me, R2 = TMS; 7, R1 = R2 = Et) when the lithium cations are chelated by 12-crown-4.

A series of butadienyl organomagnesium complexes, including 1-Li-4-(MgR)-butadienes, 1,4-bis(MgR)-butadienes, and 1-Mg-4-(MgR)-butadiene were synthesized starting with 1,4-dilithio butadienes via the transmetalation reaction between alkenyllithium bond and alkenylmagnesium bond. Single-crystal X-ray structural analysis of these butadienyl organomagnesiates revealed unique bonding modes. Study on their structural transformation demonstrated that 1-Li-4-(MgR)-butadiene is the key intermediate in the reaction process leading to the formation of 1,4-bis(MgR)-butadiene and 1-Mg-4-(MgR)-butadiene.

A Rh(I)-catalyzed intramolecular cis-carbosilylation of alkynes was achieved. The cleavage of an alkyl–Si bond in a trimethylsilyl group of 8-alkynyl naphthalene derivatives was followed by cis-addition to the alkynyl moiety, affording silatricyclic compounds in good yields.

Efficient synthesis and structure elucidation of carbon-calcium σ-bonded compounds are of remarkable interest and importance in organometallic chemistry of the heavier s-block metals. In this paper, we report that styryl and biphenyl calcium complexes with well-defined structures can be facilely obtained via metathesis reaction between their corresponding dilithio compound and calcium iodide. Single-crystal X-ray structural analysis of these calcium complexes revealed their unique iodide-bridged or dicalcium-bridged structures. Their reactivity toward nitrous oxide was disclosed.