Imido Nitrogen Research Articles

Structural Tuning of the Imido Bonds in (Arylimido)vanadium(V) Compounds

Abstract Structural characterization of (arylimido)vanadium(V) compounds was demonstrated to elucidate the ligand effect on the nature of the imido bonds. In the case of the triisopropoxide ligand, the nitrogen of the imido bond is suggested to possess an sp-hybridized character although the participation of an sp2-hybridized character is indicated with the imido nitrogen derived from the triethanolaminate ligand.

Monodentate imido coordination of 2-aminodiphenylamine to rhenium(V)

The complex trans-[Re(ada)Cl3(PPh3)2] (H2ada = 2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre solely through a dianionic imido nitrogen, with distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re–Cl bond trans to the Re=N bond is shorter than the two equatorial Re–Cl bonds. The Re = N–C bond angle of the phenylimido moiety equals 178.7(4)°.

Imido, amino and amido coordination of diaminouracil to rhenium(V)

Reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3-dimethyl-2,4-dioxopyrimidine (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2] (ReO4) (1). A single-crystal X-ray crystal structure shows that ddd is coordinated as a monodentate through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated as a bidentate via a neutral amino nitrogen atom, trans to the imido nitrogen, and a singly deprotonated amido nitrogen atom, trans to the iodide.

The role of ammonia in atomic layer deposition of tungsten nitride

The authors use density functional theory to investigate the atomic layer deposition of WN using bis-(tert-butylimido)-bis(dimethylamido)tungsten and ammonia. They find that ligand exchange involving two proton transfers from ammonia to the imido nitrogen eliminating tert-butylamine is the lowest barrier pathway. Elimination of isobutene by β-hydrogen transfer from the tert-butyl group involves high barriers. NH3 catalytically lowers the β-hydrogen transfer barrier; however, the catalyzed barrier is still substantially above the barrier for the ligand exchange reaction. Thus, incorporation of nitrogen from ammonia is favored over mechanisms that incorporate nitrogen from the precursor, and ammonia acts as a reactant in this system rather than a catalyst.

Synthesis and crystal structure of a rhenium(V) complex containing a tridentate imido-coordinated Schiff base

The complex salt trans-[Re(mps)Cl(PPh3)2](ReO4) (1) (H3mps = N-(2-amino-3-methylphenyl)salicylideneimine) was prepared by reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H3mps. The compound was characterized by spectroscopy and X-ray crystallography. The results show that the trianionic ligand mps acts as a tridentate chelate via the doubly deprotonated amino nitrogen (which is present in 1 as an imide), the neutral imino nitrogen and the deprotonated phenolic oxygen atoms. The imido nitrogen and phenolate oxygen atoms coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre.

Electronic Structure of Trigonal-Planar Transition-Metal-Imido Complexes: Spin-State Energetics, Spin-Density Profiles, and the Remarkable Performance of the OLYP Functional.

We have carried out a detailed multifunctional density functional theory study of first-row transition-metal (Cr to Cu) β-diketiminato ("nacnac") imido and oxo complexes. All the complexes studied exhibit essentially the same d-orbital energy ordering, which is a1 (dx(2)-z(2)) ≤ a2 (dxy) ≤ a1 (dy2) < b2 (dyz) < b1 (dxz), where the metal-imido vector is identified with the z axis and metal-N3 plane is identified with the xz plane. A curious aspect of this orbital ordering is that the metal dx(2)-z(2) orbital, one of whose lobes points directly at the imido nitrogen, is considerably lower in energy than the dπ orbitals. We have determined that the remarkable stability of the dσ-type orbitals owes largely to the way these orbitals hybridize or "shape-shift" as a result of the absence of ligands trans or equatorial with respect to the imido (or oxo) group. Of the many functionals examined, OLYP and OPBE, based on the Handy-Cohen OPTX exchange functional, appear to provide the best overall description of the spin-state energetics of the various complexes. In particular, these two functionals predict an S = (3)/2 ground state for Fe(III) nacnac imido complexes and an S = 0 ground state for Co(III) nacnac imido complexes, as observed experimentally. In contrast, classic pure functionals such as PW91 predict S = (1)/2 ground states or at best equienergetic S = (1)/2 and S = (3)/2 states for the Fe(III) imido complexes, while hybrid functionals such as B3LYP and O3LYP predict S = 1 or 2 ground states for the Co(III) nacnac imido complexes.

Formation of nitroxide radicals from secondary amines and peracids: A peroxyl radical oxidation pathway derived from electron spin resonance detection and density functional theory calculation

By electron spin resonance (ESR) detection and quantum chemical calculation based on the density functional theory (DFT) at the B3LYP/6-31G(d) level, we found that the formation of nitroxide radicals from secondary amines and peracids is a peroxyl radical oxidation reaction, where peroxyl radicals are the reactive intermediates of peracids in the oxidation. The DFT calculation revealed the transition structures and activation barriers of oxidizing pyrrolidine by the peroxyl radicals of peracetic acid and percarboximidic acid. Their barriers are 11.75 and 12.35 kcal/mol, respectively, showing that the peroxyl radicals have high reactivity on secondary amines. A reaction path calculation (IRC) of the oxidation of pyrrolidine by the peroxyl radical of percarboximidic acid illustrated the process of the formation of nitroxide radical: firstly, the terminal oxygen atom of the peroxyl radical R O O attacks the nitrogen atom of secondary amine and forms a N O bond, and then the hydrogen atom from the N H of the secondary amine is transferred to the imido nitrogen atom or the carbonyl oxygen atom of peracid and finally forms a new N H or O H bond.

Bonding in Low-Coordinate Environments: Electronic Structure of Pseudotetrahedral Iron-Imido Complexes.

A detailed density functional theory study of pseudotetrahedral Fe(III/IV)-imido-phosphine complexes has yielded a host of new insights. The calculations confirm dxy(2)dx(2)-y(2)(2)dz(2)(1) (or dδ(2)dδ'(2)dσ(1)) electronic configurations for Fe(III)-imido complexes of this type, as previously proposed, where the z direction may be identified with the Fe-Nimido vector. However, geometry optimization of a sterically unencumbered model complex indicated a bent (162°) imido linkage, in sharp contrast to the linear imido groups present in the sterically hindered complexes that have been studied experimentally. Under C3v symmetry, the Fe(III)-imido molecular orbital (MO) energy-level diagram indicates the existence of near-degenerate (2)A1 and (2)E states, and accordingly, the bending of the imido group appears to be ascribable to a pseudo-Jahn-Teller distortion. For Fe(IV)-imido complexes, our calculations indicate a dxy(2)dx(2)-y(2)(1)dz(2)(1) (or dδ(2)dδ'(1)dσ(1)) electronic configuration, which is somewhat different from the dxy(1)dx(2)-y(2)(1)dz(2)(2) (or dδ(1)dδ'(1)dσ(2)) configuration proposed in the literature. Not surprisingly, for a sterically unencumbered Fe(IV)-imido complex, the degenerate (3)E state (under C3v symmetry) results in a mild Jahn-Teller distortion and a slightly bent (173°) imido linkage (on relaxing the symmetry constraint). The calculations also shed light on the surprising stability of the dz(2)-based MO, which points directly at the imido nitrogen, relative to the dπ-based MOs. The low-coordinate nature of the complexes [Formula: see text] the absence of equatorial ligands and of a ligand trans with respect to the imido ligand [Formula: see text] plays a key role in stabilizing the dz(2) orbital as well as the complexes as a whole. The electronic configurations of Fe(IV)-imido porphyrins are radically different from that of the pseudotetrahedral complexes studied here, and we have speculated that these differences may well account for the nonobservation so far of Fe(IV)-imido porphyrins.

Monodentate imido coordination of 1,2-diaminobenzene to rhenium(V)

The complex trans-[Re(dab)Cl3(PPh3)2] (H2dab = 1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre only through a dianionic imido nitrogen to give a distorted octahedral coordination geometry around the metal ion.

Reaction of Phosphoranes with Mo(N-2,6-i-Pr2C6H3)(CHCMe3)[OCMe(CF3)2]2: Synthesis and Reactivity of an Anionic Imido Alkylidyne Complex

The reaction of Ph3PCH2 with Mo(NAr)(CHCMe3)[OCMe(CF3)2]2 (Ar = 2,6-i-Pr2C6H3) produces the anionic alkylidyne complex {Ph3PMe}{Mo(NAr)(CCMe3)[OCMe(CF3)2]2}. An X-ray structure determination of the complex reveals a bent Mo−N−C angle for the imido group, as expected when a metal−carbon triple bond is present. The anion has been shown to react with electrophiles predominantly at the imido nitrogen.

A rhenium(V) complex containing a terdentate chelate with an imido donor atom: synthesis and structure of [Re(aps)I(PPh3)2]I (H3aps = N-(2-aminophenyl)-salicylideneimine)

The complex salt trans-[Re(aps)I(PPh3)2]I (1) (H3aps = N-(2-aminophenyl)-salicylideneimine) was prepared by the reaction of trans-[ReO(OEt)I2(PPh3)2] in ethanol. The compound was characterized by vibrational and 1H NMR spectrometry, and by X-ray crystallography. The trianionic ligand aps acts as a terdentate chelate via the doubly deprotonated amino nitrogen (which is present in 1 as an imide), the imino nitrogen and the deprotonated phenolic oxygen atoms. The imido nitrogen and phenolate oxygen atoms coordinate trans to one another to give distorted octahedral geometry around the rhenium(V) centre.

Monodentate imido and bidentate aminophenolate coordination of 2-aminophenol in rhenium(V) complexes

Reactions of trans-[ReOCl3(PPh3)2] and trans-[ReO(OEt)I2(PPh3)2] with 2-aminophenol (H2ap) in acetonitrile led to the formation of cis-[ReOCl2(Hap)(PPh3)] (1) and trans-[Re(ap)(Hap)I(PPh3)2]I (2), respectively. The X-ray crystal structures show that Hap is coordinated as a bidentate chelate via the neutral amino nitrogen and deprotonated phenolate oxygen, and ap is coordinated as a monodentate through the imido nitrogen. The complexes have been characterized by IR spectroscopy, NMR spectrometry and X-ray crystallography. The bite angle of the Hap chelate is 76.9(1)° and 76.0(1)° in 1 and 2, respectively.

Synthesis, Structure, and Characterization of Molybdenum(VI) Imido Complexes with N-Salicylidene-2-aminophenol

Diimido complexes of the type Mo(NAr)2Cl2(dme) (dme = 1,2-dimethoxyethane) react with N-salicylidene-2-aminophenol (sapH2) in methanol in the presence of 2 equiv of triethylamine to form complexes with the general formula Mo(NAr)(1,2-OC6H4NH)(sap). The structures of three of these compounds (NAr = 2,6-dimethylphenylimido (1), 2,4,6-trimethylphenylimido (2), 2-tert-butylphenylimido3) have been determined by X-ray crystallography. The coordination sphere around the Mo is a distorted octahedron. The oxygen from the 2-aminophenol is trans to the imido nitrogen, whereas the amido nitrogen and the tridentate sap occupy the four equatorial positions. The Mo-N-C imido linkages have angles of 167.5(2) degrees (1), 163.2(2) degrees (2), and 162.4(1) degrees (3). A precursor complex to the imido-amido complex, Mo(NAr)(sap)(OCH3)2 (4, NAr = 2,4,6-trimethylphenylimido), has been isolated and characterized. Compound 4 reacts with 2-aminophenol to form 2, with 2-aminothiophenol to form Mo(NAr)(1,2-SC6H4NH)(sap) (5), with catechol to form Mo(NAr)(1,2-OC6H4O)(sap) (6), with naphthalene-2,3-diol to form Mo(NAr)(naphthalene-2,3-diolate)(sap) (7), with 1,2-benzenedithiol to form Mo(NAr)(1,2-SC6H4S)(sap) (8), and with 1,2-phenylenediamine to form Mo(NAr)(1,2-HNC6H4NH)(sap) (9). The structures of compounds 5-9 have been determined by X-ray crystallography. With the exception of compound 8, the structures are similar to those of 1,2, and 3, with the bidentate ligand occupying one axial and one equatorial position. In 8, 1,2-benzendithiolate occupies two equatorial positions, and the nitrogen from sap is located trans to the imido nitrogen. All complexes were characterized by 1H NMR spectroscopy, cyclic voltammetry, and UV-vis spectroscopy. When a solution of 4 is exposed to moisture-containing air, MoO2(sap)(CH3OH) (10) is formed. The structure of 10 was also determined.

Synthesis and structure of the cyclic amido bismuth imide, {[(Me 3Si) 2N]Bi[μ-N(SiMe 3)]} 2, via loss of SiMe 3 from a [N(SiMe 3) 2] 1− ligand

The synthesis of Bi[N(SiMe 3) 2] 3 from BiCl 3 and KN(SiMe 3) 2 generates an unusual amido bismuth imide by-product, {[(Me 3Si) 2N]Bi[μ-N(SiMe 3)]} 2, evidently formed via Si N bond cleavage. X-ray diffraction shows that the complex contains a planar Bi 2N 2 ring with tetrahedral bismuth and trigonal planar imido nitrogen atoms.

Titanium Imido Complexes of Cyclooctatetraenyl Ligands

Reaction of [Ti(NR)Cl2(py)3] (R=tBu or 2,6-iPr2C6H3) with K(2)[COT] (COT=C8H8) or Li2[COT''] (COT''=1,4-C8H6(SiMe3)2) gave the monomeric complexes [Ti(NR)(eta8-COT)] or [Ti(NR)(eta8-COT'')], respectively. The pseudo-two coordinate, "pogo stick" geometry for these complexes is unique in both early transition-metal and cyclooctatetraenyl ligand chemistry. In contrast, reaction of [Ti(N-2,6-Me2C6H3)Cl2(py)3] with K2[COT] gave the mu-imido-bridged dimer [Ti2(mu-N-2,6-Me2C6H3)2(eta8-COT)2]. It appears that as the steric bulk of the imido and C8 ring substituents are decreased, dimerisation becomes more favourable. Aryl imido COT complexes were also prepared by imido ligand exchange reactions between anilines and [Ti(NtBu)(eta(8)-COT)] or [Ti(NtBu)(eta(8)-COT'')]. The complexes [Ti(NtBu)(eta(8)-COT)], [Ti(N-2,6-iPr2C6H3)2(eta8-COT)] and [Ti2(mu-N-2,6-Me2C6H3)2(eta8-COT)2] have been crystallographically characterised. The electronic structures of both the monomeric and dimeric complexes have been investigated by using density functional theory (DFT) calculations and gas-phase photoelectron spectroscopy. The most striking aspect of the bonding is that binding to the imido nitrogen atom is primarily through sigma and pi interactions, whereas that to the COT or COT'' ring is almost exclusively through delta symmetry orbitals. A DFT-based comparison between the bonding in [Ti(NtBu)(eta8-COT)] and the bonding in the previously reported late transition-metal "pogo stick"complexes [Os(NtBu)(eta6-C6Me6)], [Ir(NtBu)(eta5-C5Me5)] and [Ni(NO)(eta5-C5H5)] has also been undertaken.

Rhenium Chemistry of Azooximes: Oxygen Atom Transfer, Azoimine Chelation, and Imine−Oxime Contrast

The concerned azooximes (L1OH, 1) are of type p-X-C6H4C(N2Ph)(NOH) (X = H, Me, Cl). The reaction of [Re(MeCN)Cl3(PPh3)2] with [Ag(L1OH)(L1O)] in cold dichloromethane-acetonitrile solvent has furnished the green colored ionized azoimine complex [ReV(O)Cl(PPh3)2(L1)](PF6), 2. In effect L1O- has undergone oxidative addition, the oxygen atom being transferred to the metal site. Upon treatment of [ReV(NPh)Cl3(PPh3)2] with L1OH in solution, the neutral azoimine complex [ReV(NPh)Cl3(L1H)], 3, resulted due to the spontaneous transfer of the oxime oxygen atom to a PPh3 ligand, which is eliminated as OPPh3. In contrast, the oxime of 2-acetylpyridine (L2OH, 4) did not undergo oxygen atom transfer and simply afforded the imine-oxime complex [ReV(NC6H4Y)Cl2(PPh3)(L2O)], 5, upon reacting with [ReV(NC6H4Y)Cl3(PPh3)2] (Y = H, Me, Cl). The spectral and electrochemical properties of 2, 3, and 5 and the structures of three representative compounds are reported. In the cation of 2 (X = H) the two PPh3 ligands lie trans to each other and the equatorial plane is defined by the five-membered azoimine chelate ring and the oxo and chloro ligands. The oxo ligand which forms a model triple bond (Re-O length 1.616(6) A) lies cis to the imine-N atom. In 3 (X = Cl) the ReCl3 fragment has meridional geometry and the imido nitrogen lies trans to the imine nitrogen of the planar azoimine chelate ring. In 5 x H2O (Y = Me), the Cl, oximato-N, and P atoms define an equatorial plane and the pyridine-N lies trans to the imido-N. The water of crystallization is hydrogen bonded to the oximato oxygen atom (O...O, 2.829(5) A). Reaction models in which chelation of the azooxime precedes oxygen atom transfer are proposed on the basis of oxophilicity of trivalent rhenium, Lewis acid activity of pentavalent rhenium, electron withdrawal by the azo group, and observed relative disposition of ligands in products.

Synthesis, Reactivity, and Computational Studies of the Cationic Tungsten Methyl Complex [W(NPh)(N2Npy)Me]+ and Related Compounds (N2Npy = MeC(2-C5H4N)(CH2NSiMe3)2)

Reaction of the dimethyl complex W(NPh)(N2Npy)Me2 (1) (N2Npy = MeC(2-C5H4N)(CH2NSiMe3)2) with either BArF3 or [Ph3C][BArF4] (ArF = C6F5) gave quantitative conversion to the monomethyl cation [W(NPh)(N2Npy)Me]+ (2+). In contrast, reaction of 1 with [PhMe2NH][BArF4] gave [W(NPh)(HN2Npy)Me2][BArF4] (3-BArF4) by protonation of one of the amido nitrogen atoms of N2Npy. Reaction of cationic 2+ with MeCN or THF gave the labile adducts [W(NPh)(N2Npy)Me(L)]+ (L = MeCN (4+) or THF (5+)). For comparison the neutral tantalum derivatives Ta(NtBu)(N2Npy)R (R = Me (6) or η1-allyl (7)) were synthesized by reaction of Ta(NtBu)(N2Npy)Cl(py) with MeLi or (allyl)MgCl. Compound 6, valence isoelectronic with 2+, was crystallographically characterized. Although both 2+ and 6 possess trigonal bipyramidal geometries at the metal, the methyl ligand in 2+ lies in the equatorial plane (with NPh trans to pyridyl), whereas in 6 the opposite arrangement of methyl and imido ligands is found. Reaction of 1 with 0.5 equiv of BArF3 gave the fluxional Me-bridged cation [{W(NPh)(N2Npy)Me}2(μ-Me)]+ (8+); 8+ was also formed by direct reaction of 1 with 2+. The methyl cation 2+ underwent facile methyl group exchange with Cp2ZrMe2 and ZnMe2 as established by spin saturation transfer and deuterium labeling studies. Although a stable intermediate was not spectroscopically observed for either reaction, for the latter case a likely adduct was identified by DFT calculations on a model system and features coordination of Zn to the imido nitrogen and a Zn−Me···W interaction. Reaction of 2+ with AlMe3 formed [W{MeC(2-C5H4NAlMe)(CHNSiMe3)(CH2NSiMe3)}(μ-NPh)Me2]+ (9+) and CH4 by deprotonation of a CH2 linkage of N2Npy. DFT (B3PW91) calculations on model systems of the type M(NR){HC(2-C5H4N)(CH2SiH3)2}(X) (X = Cl, Me) showed that there is an unambiguous electronic preference for the imido ligand to lie trans to the pyridyl nitrogen. This geometry allows optimal π-donation from the imido and the amido nitrogen atoms. Inclusion of the steric bulk of the SiMe3 groups and the R group (Ph or tBu) on the imido ligand through ONIOM(B3PW91:UFF) calculations showed that the underlying electronic preference for the imido ligand to be trans to pyridyl can be reversed because of increased steric repulsions between the imido and amido N-substituents in this isomer. These cause a misdirection of the amido lone pair π-donation, which in turn destabilizes the metal−imido ligand π-bonding.

The crystal structure of a novel copper(II) complex with asymmetric ligand derived from l-histidine.

The crystal structure of a novel copper(II) complex with a potentially hexadentate Schiff base ligand derived from l-histidine has been solved by a single-crystal X-ray diffraction method at pH 7.4. The copper(II) ion is coordinated asymmetrically by a tetradentate ligand with the amino and imidazole imido nitrogen atoms on one side versus imino nitrogen and carboxylate oxygen atoms on the other side in a distorted square-planar geometry. The formation of an infinite chain through carboxylate coordination is observed. The novel ligand is obtained by the reaction between the l-histidine molecules coordinated to copper(II) and 4-hydroxy-4-methylpentan-2-one formed by aldol condensation of acetone. This complex provides insights into a possible structural arrangement between copper(II) and l-histidine which is physiologically important and abundantly present in biological systems.

The reaction of the cis-dioxorhenium(V) core with N, O-donor ligands: mono and bidentate coordination of 3-methyl-2-aminophenol

The reaction of cis-[ReO 2I(PPh 3) 2] with 3-methyl-2-aminophenol (H 2map) in ethanol led to the formation of trans-[Re(map)(Hmap)I(PPh 3) 2]I. The X-ray crystal structure shows that the ligand map is coordinated monodentately through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hmap is coordinated via the neutral amino nitrogen and the singly deprotonated phenolate oxygen, which is coordinated trans to the imido nitrogen. In benzene equimolar quantities of cis-[ReO 2I(PPh 3) 2] and 4-methyl-2-aminophenol (H 2amp) produced the five-coordinate cis-[ReO 2(Hamp)(PPh 3)]. A twofold molar excess of 2-aminophenol (H 2ap) yielded the six-coordinate [ReO(Hap)(ap)(PPh 3)]. The chelate ap is coordinated through the deprotonated phenolate oxygen and the singly deprotonated amino nitrogen (amide).

P-N bond length alterations monitored by infrared absorption and Fourier transform Raman spectroscopy in combination with density functional theory calculations.

Fourier transform (FT) Raman and infrared spectroscopy in combination with density functional theory calculations have been applied to the vibrational characterization of the dimeric zinc diphenylphosphanyl(trimethylsilyl)amide complex [(Me3Si)2NZnPh2PNSiMe3]2 and the ortho-metallated species [Li(o-C6H4PPh2NSiMe3)]2 x Et2O in relation to their parent starting materials diphenylphosphanyl (trimethylsilyl)amine Ph2P-N(H)SiMe3 and iminophosphorane Ph3P=NSiMe3. The spectroscopic changes evidenced in the spectra were correlated with the structural parameters in order to provide insight as to what extent the P-N bond is affected by the coordination to the metal center. The employment of density functional theory (DFT) calculations in addition to these spectroscopic methods offers the possibility of predicting whether the Lewis-basic imido nitrogen atom is involved in coordination not only in the solid state, but also in the gas phase.