Triazenide Ligand Research Articles

Ruthenium complexes with triazenide ligands bearing an N-heterocyclic moiety, and their catalytic properties in the reduction of nitroarenes.

A series of ruthenium complexes of formulae [RuCl(triazenide)(p-cymene)] have been synthesized using as ligand a triazenide monofunctionalized with an N-heterocyclic moiety. Nuclear magnetic resonance, high resolution mass spectrometry and X-ray diffraction were used to characterize the triazenide ligands and their complexes. In addition, these ruthenium complexes catalyzed the reduction of nitrobenzene to aniline in the presence of sodium borohydride and ethanol as solvent at room temperature. Notably, complex 5 was especially active in the reduction of nitroarenes substituted at the aromatic ring with electron-withdrawing or electron-donating fuctional groups affording the desired arylamines in good to excellent yields (80-100%). The role of the N-heterocyclic moiety on catalysis was explored.

Bis‐Silyl‐triazenide ligands in alkaline‐earth metal chemistry

AbstractMonoanionic N,N‐chelating triazenide ligands, [R‐NNN‐R]−, are compared to formamidinate or β‐diketiminate ligands considerably less electron‐donating and therefore potentially suitable for stabilizing electron rich metals in low oxidations states. A feature reported for silyl‐substituted triazenide ligands, is their ability to eliminate N2 resulting in (R3Si)2N− anions. Here we describe a series of group 1 and 2 metal complexes with the very bulky bis‐silyl‐triazenide ligand [tBu3Si‐NNN‐SitBu3]−. Heteroleptic complexes could be isolated for Mg: {[(tBu3Si)2N3]MgnBu}2 or {[(tBu3Si)2N3]MgI}2, including its ether adducts. Despite bulky silyl substituents, the ligand did not stabilize heteroleptic [(tBu3Si)2N3]AeN(SiMe3)2 complexes for Ca, Sr and Ba and only homoleptic Ae[(tBu3Si)2N3]2 complexes were isolated. Thermal decomposition of these complexes did result in N2 elimination and formation of the expected amide complexes. Reduction of [(tBu3Si)2N3]MgI ⋅ (Et2O) with KC8 in Et2O led to the formation of a MgI complex with a Mg−Mg bond length of 2.902(1) Å. As only one of the Mg centres shows coordination with a Et2O ligand, this is a rare example of an asymmetric Mg−Mg bond. This MgI complex is rather unstable in benzene solution, likely due to reduction of the ligand system. Triazenide ligands are therefore not suitable for stabilization of group 2 metals in low oxidation states.

Synthesis, Structure and Thermal Properties of Volatile Indium and Gallium Triazenides**

AbstractIndium and gallium nitride are important semi‐conductor materials with desirable properties for high‐frequency and power electronics. We have previously demonstrated high‐quality ALD grown InN and GaN using the hexacoordinated 1,3‐diisopropyltriazenide In(III) and Ga(III) precursors. Herein we report the structural and thermal properties their analogues employing combinations of isopropyl, sec‐butyl and tert‐butyltriazenide alkyl groups on the exocyclic nitrogen of the triazenide ligand. The new triazenide compounds were all found to be volatile (80‐120 °C, 0.5 mbar) and showed very good thermal stability (200 and 300 °C). These new triazenide analogues provide a set of precursors whose thermal properties are determined and can be accordingly tailored by strategic choice of exocyclic nitrogen alkyl substituents.

Synthesis and Thermal Study of Hexacoordinated Aluminum(III) Triazenides for Use in Atomic Layer Deposition.

Amidinate and guanidinate ligands have been used extensively to produce volatile and thermally stable precursors for atomic layer deposition. The triazenide ligand is relatively unexplored as an alternative ligand system. Herein, we present six new Al(III) complexes bearing three sets of a 1,3-dialkyltriazenide ligand. These complexes volatilize quantitatively in a single step with onset volatilization temperatures of ∼150 °C and 1 Torr vapor pressures of ∼134 °C. Differential scanning calorimetry revealed that these Al(III) complexes exhibited exothermic events that overlapped with the temperatures of their mass loss events in thermogravimetric analysis. Using quantum chemical density functional theory computations, we found a decomposition pathway that transforms the relatively large hexacoordinated Al(III) precursor into a smaller dicoordinated complex. The pathway relies on previously unexplored interligand proton migrations. These new Al(III) triazenides provide a series of alternative precursors with unique thermal properties that could be highly advantageous for vapor deposition processes of Al containing materials.

Base-free transfer hydrogenation of aryl-ketones, alkyl-ketones and alkenones catalyzed by an IrIIICp* complex bearing a triazenide ligand functionalized with pyrazole

An IrIIICp* complex (2) bearing a triazenide ligand functionalized with pyrazole was synthesized and fully characterized by spectroscopic methods and the structure confirmed by X-ray diffraction studies. The catalytic activity of 2 and the control complex 3, which lacks of pyrazole in its structure, was evaluated in the reduction of aryl-ketones, alkyl-ketones, α,β-unsaturated and γ,δ-unsaturated ketones. The catalytic system, using either 2 or 3, exhibited good to excellent selectivity when tested with ketones and alkenones at 90 °C in 2-propanol as hydrogen source under base-free conditions. Reactivity of 2 in 2-propanol and NaH gave a neutral metal hydride (4) while in the absence of base gave two major cationic hydrides species (5 and 6).

Bulky bis(aryl)triazenides: just aspiring amidinates? A structural and spectroscopic study.

The synthesis and molecular structures (by single crystal X-ray diffraction) of s-, p- and d-metal complexes of the sterically demanding N,N'-bis(2,6-diisopropylphenyl)triazenide are reported and the spectroscopic (NMR spectroscopy and infrared spectroscopy) and physical properties of these complexes compared to related formamidinate complexes. Through the use of infrared spectroscopy the σ-donor capacity of this ligand is demonstrated to be reduced relative to the structurally isomorphous formamidinate congener, which supports previously advanced theoretical calcluations and DFT results reported herein. These electronic differences are highlighted by the stark contrast in reaction outcomes at rhodium; where [(Dipp2N3)Rh(CO)2] (1) is an isolable, stable complex and the formamidinate complex is not. The coordination chemistry of the triazenide ligand for the s-block metal complexes (M = Li, Na, K) has been shown to give structurally isomorphous complexes to the formamidinate analogue. In contrast to the amidinate complexes, these complexes show extreme lability of coordinated, volatile Lewis-bases, which in turn-yields the highly insoluble base-free triazenide complexes. These complexes are also synthesized directly in the absence of donor solvents. This triazenide ligand has proven to be a suitable ligand for stabilising reactive main group hydrides of Group 13 (M = Ga, In) and attempts at the analogous thallium hydride complex by halide-hydride exchange are reported. Finally attempts at the synthesis of low valent main group complexes are reported ([MIL], M = In, Ga) are also reported, which yield instead disproportionation products ([MIIIXL2], M = Ga, In; [{MIIXL}2], M = Ga).

Dipalladium(I) complexes of ortho- and para-functionalized 1,3-bis(aryl)triazenide ligands: Synthesis, structure and catalytic activity

The synthesis and characterization of a series dipalladium(I) complexes of formulae [Pd{1-[2′-(methoxycarbonyl)phenyl]-3-[4′-X-phenyl]triazenide}]2 [X = F (4), Cl (5), Br (6)] are reported. The crystal structure of complex 4 was determined by X-ray diffraction studies. The previously reported dipalladium(I) 1–3 as well as the new complexes 4–6 were used as catalysts in the Heck and Suzuki couplings of different p-substituted bromobenzenes.

Kinetic stabilization of low-oxidation state and terminal hydrido main group metal complexes by a sterically demanding N,N'-bis(2,6-terphenyl)triazenide.

A sterically demanding N,N'-bis(2,6-terphenyl)triazenide was employed to stabilize a number of low-coordinate main group metal terminal hydride complexes. These complexes display enhanced thermal stabilities relative to analogous complexes ligated by β-diketiminates, which we attribute to the steric shielding of the metal hydride moiety by the ligand. We also show this triazenide ligand can stabilize low-oxidation state Group 13 metals. DFT calculations conducted on these triazenide ligated Group 13 metal(i) complexes revealed they possess a narrower HOMO-LUMO gap relative to analogous complexes ligated by other monoanionic N,N'-ligands. In addition, several heteroleptic Group 13 metal(iii) and Group 14 metal(ii) complexes featuring this triazenide are reported.

RutheniumII(p-cymene) complexes bearing ligands of the type 1-[2′-(methoxycarbonyl)phenyl]-3-[4′-X-phenyl]triazenide (X = F, Cl, Br, I): Synthesis, structure and catalytic activity

The synthesis and characterization of triazenes of the type 1-[2′-(methoxycarbonyl)phenyl]-3-[4′-X-phenyl]triazene [X=F (1), Cl (2), Br (3), I (4)] as precursors of triazenide ligands for the preparation of their complexes of formula [Ru{1-(2′-methoxycarbonylphenyl)-3-(4′-X-phenyl)triazenide}(Cl)(p-cymene)] [X=F (6), Cl (7), Br (8), I (9), CH3 (10)] are reported. Molecular structures for all four triazenes (1–4), and of complexes 6, 9 and 10 were determined by X-ray diffraction studies. Complexes 6–10 were tested as catalysts in the transfer hydrogenation of acetophenone in the presence and in the absence of base. The best results were obtained in the presence of base with yields in the range of 86–94%, whereas even in the absence of base yields in the range 42–65% were achieved.

Hetero- and Homoleptic Magnesium Triazenides

Using monoanionic triazenide ligands derived from biphenyl and m-terphenyl substituted triazenes Dmp(Tph)N3H (1a), (Me4Ter)2N3H (1b) or Dmp(Mph)N3H (1c) (Dmp = 2,6-Mes2C6H3 with Mes = 2,4,6-Me3C6H2; Me4Ter = 2,6-(3,5-Me2C6H3)2C6H3; Mph = 2-MesC6H4; Tph = 2-TripC6H4 with Trip = 2,4,6-i-Pr3C6H2), several magnesium triazenides were synthesized. Heteroleptic complexes [Mg(N3Ar2)I(OEt2)] (Ar2 = Dmp/Tph (2a), (Me4Ter)2 (2b) were obtained from metalation of the corresponding triazenes with di-n-butylmagnesium followed by reaction with iodine in diethyl ether as the solvent in high yields. Replacing diethyl ether by n-heptane afforded trinuclear compounds [Mg3(N3Ar2)2I4] (3a, 3b) in low yields in which a central MgI2 fragment is coordinated by two iodomagnesium triazenide moieties. Two unsolvated homoleptic magnesium compounds [Mg(N3Ar2)2] (4b, 4c) were obtained from di-n-butylmagnesium and triazenes 1b or 1c in a 1:2 ratio. Depending on the nature of the substituents, the magnesium center either shows the expected tetrahedral or a rather unusual square planar coordination.

Synthesis, structures and catalytic activity of 1,3-bis(aryl)triazenide(p-cymene)ruthenium(II) complexes

The synthesis, characterization, crystal structures and catalytic activity of four new 1,3-bis(aryl)triazenide(p-cymene)ruthenium(II) complexes bearing methoxycarbonyl (5), hydroxymethyl (6), acetylphenyl (7) in the ortho position, and methyl in the para position (8) of the bis(aryl)triazenide ligand are reported. These complexes were used as catalysts in the transfer hydrogenation reactions of ketones and alkenone with good to excellent yields of the corresponding alcohol. Remarkable differences in yields were obtained with those complexes with ortho substituents on the aryl group of the triazenide ligand (5–7) compared to that without ortho substituent (8). Good selectivity was also observed in the reduction of the alkenone towards the carbonyl group.

Synthesis, Crystal Structure, Solution Study and In Silico ADME Profiling of Various Asymmetric Functionalized Triazenes

Syntheses of some ligands based on asymmetric triazenes consisting 1-(2-methoxycarbonylphenyl)-3-(2-methylphenyl)triazene (1), 1-(2-methoxycarbonylphenyl)-3-(3-methylphenyl)triazene (2), 1-(2-methoxycarbonylphenyl)-3-(4-methylphenyl)triazene (3), 1-(2-methoxycarbonylphenyl)-3-(3,5-dichlorophenyl)triazene (4), 1-(4-chlorophenyl)-3-(4-methylphenyl)-triazene (5) and their related HgII complexes were reported. The characterizations were performed by FT-IR, 1H NMR and 13C NMR spectroscopies. In (3) and (4), both triazenes possess trans-conformation around the (–N=N–) bond and monomeric moieties are linked to pairs and wave-like chains through C–H···O and C–H···N hydrogen bonds which are further assembled by stacking through secondary π···π interactions [3.829(1) and 3.736(1) A]. The reaction of (1) and Hg(NO3)2 in methanol produces the corresponding HgII complex (6) where each triazenide binds to the HgII atom through two nitrogen atoms of triazenide and one oxygen atom of pendant methoxycarbonyl group forming distorted MN4O2 octahedral around the HgII atom. The stoichiometry and formation of complex (6) and (8) in methanol solution were investigated by UV–Vis titration. Moreover, Reaction of substituted 1,3-diaryltriazenes (2) and (5) with HgII salts afford a family of orange complexes (7) and (8), respectively. Finally, the chemical structures of the investigated ligands were correlated to their pharmacokinetic behaviour using five pre-calculated models implemented in VolSurf program. Polyhedron around HgII atom coordinated by two triazenide ligands in an octahedron fashion.

Triazenides as Suitable Ligands in the Synthesis of Palladium Compounds in Three Different Oxidation States: I, II, and III

New orthometalated dinuclear triazenide palladium(II) compounds of the general formula Pd2[(C6H4)PPh2]2[R–N–N–N–R]2 (R = C6H5, 3a; o-BrC6H4, o-3b; o-MeOC6H4, o-3c; o-MeC6H4, o-3d ; p-BrC6H4, p-3b; p-MeOC6H4, p-3c; p-MeC6H4, p-3d) have been synthesized and structurally characterized. The characteristics of these compounds were compared with the isoelectronic formamidinate derivatives. These triazenide compounds have been suitable starting products in the synthesis of new not so common dinuclear palladium(I) compounds and new unusual palladium(III) ones. In the presence of an excess of the triazenide ligand, compounds o-3b and o-3c underwent a reduction process giving dinuclear palladium(I) compounds, Pd2[R–N–N–N–R]2 (R = o-BrC6H4, o-4b; R = o-MeOC6H4, o-4c). DFT calculations verified the importance of the mostly noncovalent Pd···Br or Pd···OMe axial interactions on the stability of these compounds. Under cyclic voltammetric conditions, compounds 3 with the only exception of compound o-3b, were found to und...

Mixed-ligand 1,3-diaryltriazenide complexes of ruthenium: Synthesis, structure and catalytic properties

Reaction of 1,3-diaryltriazenes (abbreviated in general as HL-R, where H represents the dissociable N–H proton and R is the para substituent (R=OCH3, CH3, H, Cl, NO2) on the aryl fragment) with [Ru(PPh3)2(CO)2Cl2] in 2-methoxyethanol in the presence of a base (NEt3) affords a family of yellow complexes of the type [Ru(PPh3)2(L-R)(CO)(H)], where the 1,3-diaryltriazenes are coordinated as monoanionic bidentate NN-donors. Two triphenylphosphines, a hydride and a carbonyl are also coordinated to ruthenium. The triphenylphosphines are mutually trans, and the hydride and carbonyl are mutually cis. Structure of the [Ru(PPh3)2(L-H)(CO)(H)] complex has been determined by X-ray crystallography. All the complexes show intense absorptions in the visible region, which are assigned, based on DFT calculations, to transitions within orbitals of the triazenide ligand. The complexes exhibit an irreversible oxidation on the positive side of SCE and an irreversible reduction on the negative side. All the complexes are found to efficiently catalyze transfer hydrogenation reactions.

Synthesis, characterization and crystal structures of HgII complexes with asymmetric ortho-functionalized 1,3-bis(aryl)triazenide ligands

The synthesis of two [Hg(L1)2] and [Hg(L2)2] complexes using asymmetric triazenes as ligands are reported. The triazene ligands are substituted with cyano and chloride groups in the ortho positions of the aryl rings (where HL1 and HL2 are 1-(2-ethoxyphenyl)-3-(2-cyanophenyl)triazene and 1-(2-ethoxyphenyl)-3-(2-chlorophenyl) triazene, respectively). These complexes were prepared by the reaction of corresponding triazenes with Hg(NO3)2 and were characterized by FT-IR, NMR, elemental and single crystal X-ray analyses. Both triazene ligands were found to deprotonate on coordination and act as tridentate chelating ligands forming distorted N4O2 octahedral geometry around HgII atoms. Hydrogen bonds, π⋯π and C–H⋯π stacking interactions help to the stabilization of the resulted frameworks.

Synthesis, Structure, and Solution Study of a Mercury(II) Complex with the Ligand [1‐(2‐Methoxyphenyl)‐3‐(4‐chlorophenyl)]triazene

AbstractThe title ligand, [1‐(2‐methoxyphenyl)‐3‐(4‐chlorophenyl)]triazene, HL (1), was prepared. In a reaction with Hg(NO3)2 it forms the complex [Hg(C26H22Cl2N6O2)], [HgL2] (2). Both compounds were characterized by means of X‐ray crystallography, CHN analysis, FT‐IR, 1H NMR, and 13C NMR spectroscopy. In the structure of compound 1, two independent fragments are present in the unit cell. They exhibit trans arrangement about the –N=N– double bond. The dihedral angles between two benzene rings in both fragments are 4.36 and 18.79 Å, respectively. Non‐classic C–H···N hydrogen bonding and C–H···π interactions form a layer structure along the crystallographic ab plane [110]. In compound 2, the HgII atom is hexacoordinated by two tridentate [1‐(2‐methoxyphenyl)‐3‐(4‐chlorophenyl)]triazenide ligands through a N2O2 set. In addition, in the structure of 2, monomeric complexes are connected to each other by C–H···π stacking interactions, resulting in a 2D architecture. These C–H···π edge‐to‐face interactions are present with H···π distances of 3.156 and 3.027 Å. The results of studies of the stoichiometry and formation of complex 2 in methanol solution were found to support its solid state stoichiometry.

Bis[1-(2-ethoxyphenyl)-3-(4-nitrophenyl)triazenido]mercury(II)

In the title compound, [Hg(C14H13N4O3)2], the central Hg atom (site symmetry 2) is six-coordinated by two tridentate 1-(2-eth­oxy­phen­yl)-3-(4-nitro­phen­yl)triazenide ligands through two N and one O atoms. The mononuclear complex mol­ecules are connected into two parallel chains by inter­molecular C—H⋯O hydrogen-bonding inter­actions. These chains are connected to each other by face-to-edge C—H⋯π inter­actions between the CH of the ethoxy groups and the aromatic rings, resulting in a two-dimensional architecture in the ac plane.

Design, synthesis and properties of a trinuclear copper(I) cluster with a triazenide ligand

The reaction of methyl anthranilate, sodium nitrite, and 2-aminobenzothiazole produces a new triazenide, namely, 1-[(2-carboxymethyl) benzene]-3-[benzothiazole]triazene (HL). In the presence of Et 3 N, the reaction of HL and CuCl in THF/methanol gives a trinuclear copper(I) cluster [Cu 3 L 3 ] THF CH 3 OH ( 1 THF CH 3 OH), which has been characterized by X-ray crystallography, cyclic voltammogram and emission spectrum. CV of 1 reveals two reversible waves at –0.06 and 0.83 V, which correspond to two one-electron oxidation of Cu 3 units ([Cu 3 ] 4+ /[Cu 3 ] 3+ ) and ([Cu 3 ] 5+ /[Cu 3 ] 4+ ), respectively. 1 appears photoluminescent ( λ max = 502 nm) at room temperature. In the presence of Et 3 N, the reaction of 1-[(2-carboxymethyl) benzene]-3-[benzothiazole]triazene (HL) and CuCl in THF/methanol gives a trinuclear copper(I) cluster [Cu 3 L 3 ]×THF×CH 3 OH ( 1 ×THF×CH 3 OH). CV of 1 reveals two reversible waves at - 0.06 and 0.83 V, which can be ascribed to the redox coupling of ([Cu 3 ] 4+ /[Cu 3 ] 3+ ) and ([Cu 3 ] 5+ /[Cu 3 ]4 + ), respectively. 1 appears photoluminescence (lmax = 502 nm) at room temperature.

Chlorido[1-(2-ethoxyphenyl)3-(4-nitrophenyl)triazenido]mercury(II)

In the title compound, [Hg(C14H13N4O3)Cl], the HgII atom is four-coordinated by one O atom and two N atoms from a tridentate 1-(2-eth­oxy­phen­yl)-3-(4-nitro­phen­yl)triazenide ligand and one terminal chloride ion in a distorted square-planar geometry. In the crystal structure, the mononuclear complexes are linked into pairs through C—H⋯O and C—H⋯Cl hydrogen bonds as well as π–π and C—H⋯π stacking inter­actions. In addition, weak Hg–μ6-arene π-inter­actions [mean distance of 3.667 (2) Å] are present between these dimers. The π–π stacking inter­actions are between aromatic rings with a centroid–centroid distance of 3.884 (2) Å. Moreover, edge-to-face inter­actions are present between eth­oxy CH groups and aromatic rings with H⋯π distances of 2.81 Å.

1,3-Bis(2-alkyltetrazol-5-yl)triazenes and their Fe(II), Co(II) and Ni(II) complexes: Synthesis, spectroscopy, and thermal properties. Crystal structure of Fe(II) and Co(II) 1,3-bis(2-methyltetrazol-5-yl)triazenide complexes

Complexes ML 1 2 and ML 2 2, with M = Fe II, Co II, Ni II, and 1,3-bis(2-R-tetrazol-5-yl)triazenide ligands L 1 (R = Me) and L 2 (R = tBu), have been synthesized by the reaction of corresponding 1,3-bis(2-R-tetrazol-5-yl)triazenes with metal(II) salts in basic media and characterized by IR, UV–Vis spectroscopy, thermal and X-ray diffraction analyses. Both 1,3-bis(2-R-tetrazol-5-yl)triazenes were found to deprotonate on coordination and act as tridentate chelating ligands forming distorted MN 6 octahedra around metal(II) cations.