Metal-nitrogen Bonds Research Articles

Chelate ring closing and opening behavior in cyclopentadienyl cobalt(III) complexes with pendant nitrogen functional group

Abstract Kinetic studies were performed for the chelate ring closing and opening process of cyclopentadienyl cobalt(III) complexes having a pendant N-functional group with an amine, piperidine or pyridine moiety in the side chain. The metal–nitrogen bond energy was measured. The rate of chelation by such pendant N-functionalized side chains in diiodomonocarbonyl cobalt(III) reaction intermediates is determined by the electronic density on the donor atom and the strength of the forming chelated bond. The steric factor around the donor atom plays a secondary role. On the basis of the enthalpies and entropies obtained from the kinetic studies, the process of chelate ring closing in diiodomonocarbonyl cobalt(III) reaction intermediates is via an associative pathway involving loss of CO, while the chelate ring opening process in the resulted chelators is via a metal–nitrogen bond cleavage, solvation then metal–phosphorus bond formation pathway during substitution of PPh 3 . The chelator with the most rigid arm of picolyl shows a smallest steric hindrance for incoming PPh 3 compared to the other two analogues.

Computational Studies of the Relative Rates for Migratory Insertions of Alkenes into Square-Planar, Methyl, −Amido, and −Hydroxo Complexes of Rhodium

The relative rates of the migratory insertions of alkenes into the M-X bonds of (PMe(3))(2)Rh(eta(2)-CH(2) horizontal lineCHR)(X) (R = H, Me; X = CH(3), NH(2), OH) have been analyzed by DFT calculations. These insertions are computed to form metallacycles containing a metal-carbon bond and either an agostic interaction, a dative metal-nitrogen bond, or a dative metal-oxygen bond. The computed barriers for migratory insertion into the metal-hydroxo and metal-amido bonds are lower than those for insertion into the metal-methyl bond. Application of Bader's atoms-in-molecules analysis and natural localized molecular orbital analysis implies that the barriers for alkene insertion into M-X bonds are controlled by the degree of M-X bonding in the transition state, which correlates with the degree of M-X bonding in the initial product. The Rh-X bond orders in the transition states for migratory insertion of ethylene into the Rh-NH(2) and Rh-OH bonds in (PH(3))(2)Rh(eta(2)-C(2)H(4))(NH(2)) and (PH(3))(2)Rh(eta(2)-C(2)H(4))(OH) are much larger than that in the transition state for insertion into the Rh-C bond of (PH(3))(2)Rh(eta(2)-C(2)H(4))(CH(3)). The free energy barriers for 1,2- and 2,1-insertions of propene into the rhodium complexes were also calculated, and the barrier for 1,2-insertion was found to be lower than that for 2,1-insertion. Most striking, the DeltaDeltaG(double dagger) values for 1,2- versus 2,1-insertion of propene into these rhodium complexes were calculated to increase in the order X = CH(3) < NH(2) < OH. The increasing stability of the 1,2-insertion product with increasing polarity of the C-X bonds parallels the relative stabilities of linear versus branched alkanes, amines, and alcohols.

Equilibrium, photophysical, photochemical and quantum chemical examination of anionic mercury(I) porphyrins

Hg22+ion and 5,10,15,20-tetrakis(parasulphonato-phenyl)porphyrin anion can form 2:1 (2 clusters:1 porphyrin) and 2:2 complexes, while the formation of the 1:1 species is not observable: it is only an intermediate, similarly to the cases of other large metal ions of small charge-density. The differences between mercury(I) and mercury(II) porphyrins in the composition of monoporphyrins (2:1 vs. 1:1), in the stability and the Soret absorption based on the arrangement of 2:2 complexes (asymmetric vs. probably symmetric sandwich-structure), in the kinetic behavior (molecularities and the special dimerization of HgIIP4-), in the product of the photoinduced dissociations of 2:2 bisporphyrins (free-base ligand vs. 1:1 complex) can prove that no mercury(II) porphyrins can form due to the possible disproportion of dimercury(I) ions. However, the similarities in the absorption, photophysical and photochemical features (also to other out-of-plane metalloporphyrins) suggest that the out-of-plane position of metal center and the distorted structure of complexes may be responsible for these common properties, the so-called sitting-atop characteristics. Moreover, the calculated structural data of the theoretically studied 1:1 mercury(I) porphyrin are very similar to those of HgIIP as a consequence of the charge separation in the cluster based on the strength of metal-nitrogen bonds. In the case of the 2:2 species, neither the increased distance (because of the Hg-Hg bond), nor the absence of 45° rotation of the two ligands can significantly modify the π-π interaction because its both measured and calculated absorption spectra are similar to those of HgII2P2.

Imidazolin-2-iminato Complexes of Rare Earth Metals with Very Short Metal−Nitrogen Bonds: Experimental and Theoretical Studies

The reactions of 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (Im(Dipp)NH, 1-H) with trimethylsilylmethyl lithium (LiCH(2)SiMe(3)) and anhydrous rare earth metal trichlorides MCl(3) afforded the imidazolin-2-iminato complexes [(1)MCl(2)(THF)(3)] (2a, M = Sc; 2b, M = Y; 2c, M = Lu) and [(1)GdCl(2)(THF)(2)] x [LiCl(THF)(2)] (2d). Treatment of complexes 2 with dipotassium cyclooctatetradienide, K(2)(C(8)H(8)) resulted in the formation of two- or three-legged piano-stool complexes of the type [(eta(8)-C(8)H(8))M(1)(THF)(n)] (3a, M = Sc, n = 1; 3b, M = Y, n = 2; 3c, M = Lu, n = 2; 3d, M = Gd, n = 2). X-ray diffraction analyses of all eight complexes 2 and 3 revealed the presence of very short metal-nitrogen bonds, which are among the shortest ever observed for these elements. [(eta(8)-C(8)H(8))Sc(1)(THF)] (3a) reacted with 2,6-dimethylphenyl isothiocyanate (Xy-NCS) to form the [2 + 2]-cycloaddition product 4, which contains a thioureato-N,N' moiety. The related COT-titanium complex [(eta(8)-C(8)H(8))TiCl(1)] (6) could be obtained from [(1)TiCl(3)] (5) by reaction with K(2)(C(8)H(8)) and was structurally characterized. As a theoretical analysis of the nature of the metal-nitrogen bond, density functional theory (DFT) calculations have been carried out for complexes 3a and 6 and also for the model complexes [(eta(8)-C(8)H(8))Sc(NIm(Me))] (7), [(eta(8)-C(8)H(8))Ti(NIm(Me))](+) (8), and [(eta(8)-C(8)H(8))Ti(NXy)] (9), revealing a marked similarity of the bonding in imidazolin-2-iminato and conventional imido metal complexes.

Effect of Annealing on the Properties of Indium−Tin−Oxynitride Films as Ohmic Contacts for GaN-Based Optoelectronic Devices

Indium-tin-oxynitride (ITON) films have been fabricated by rf sputtering from an indium-tin-oxide target in nitrogen plasma. The influence of postdeposition annealing up to 800 degrees C is analyzed by electrical, optical, and surface characterization of the films in comparison to indium-tin-oxide (ITO) films fabricated in argon plasma. High-temperature annealing resulted in ITO(N) films with similar carrier concentrations. However, the resistivity and optical transmittance of the ITON films were higher than those of the ITO films. Photoelectron spectroscopy revealed that nitrogen is incorporated into the ITON structure in an unbound state as well as through the formation of metal-nitrogen and oxynitride bonds that decorate oxygen vacancies. When the core level electron spectra of ITO and ITON films are compared, a correlation between carrier concentration and the incorporated nitrogen is found. Changes in ITON electrical properties are mainly induced by the release of nitrogen at temperatures above 550 degrees C. In this context, ohmic contact behavior was achieved for ITON on p-type GaN after annealing at 600 degrees C, while no ohmic contact could be realized using ITO.

TERMINAL NITRIDO AND IMIDO COMPLEXES OF THE LATE TRANSITION METALS

Compounds that contain a late transition metal-nitrogen multiple bond represent important reactive intermediate species in many useful organic and inorganic transformations. In order to understand the role that these intermediates play in reactions, it is important to have a full understanding of their electronic structure. This paper reviews the known structural motifs that occur in late transition metal nitrido and imido compounds, and provides a correlation between geometric structure and electronic structure. Also, intermediate species that have been postulated but not yet isolated are discussed, as these compounds represent exciting targets for further efforts in synthetic inorganic chemistry.

Thermochemistry of Morpholine Adducts of Some Bivalent Transition Metal Bromides

The adducts [MBr 2 (morph) n ] (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II), morph is morpholine, and n = 1.5, 2, or 3) were synthesized and characterized by melting points, elemental analysis, thermal analysis, and electronic and IR spectroscopy. From calorimetric studies in solution, the standard enthalpies of formation of the adducts and several thermochemical parameters were determined. The mean standard enthalpies of the metal-nitrogen bond were calculated.

Recoordination of a metal ion in the cavity of a crown compound: a theoretical study

The absorption spectra of styrylbenzothiazolium dye derivatives were calculated by the time-dependent density functional (TD DFT) method. The dyes of interest were (p-dimethylamino)styrylbenzothiazolium dye and its protonated form as well as aza-15(18)-crown-5(6)-containing dyes and their complexes with alkali (K+ and Na+) and alkaline-earth (Ca2+, Sr2+, and Ba2+) cations. Several low-lying conformers of the azacrown-containing dyes were considered. The electronic and geometric structures of the excited states responsible for the appearance of the long-wave (π-π*) absorption bands are studied. Complexation causes a hypsochromic shift of the long-wave absorption band correlating with the pyramidality of the crown ether nitrogen in the complex. The interaction of the cation with 3–4 solvent molecules or a counterion (ClO4−) considerably reduces this shift, especially in the conformers without the metal-nitrogen bond. In some cases, the long-wave absorption band is close to the absorption band of the free dye. Similar results were obtained using the polarizable continuum model of solvation. Excited-state structures of the free model dye and the free azacrown-containing dyes exhibit a tendency to bond alternation. Conversely, the cationic complexes of the crown-containing dyes and the protonated model dye exhibit a tendency to bond equalization in the excited state. The changes in the excited-state geometries of the free dyes and their complexes account for the complexation-induced fluorescence enhancement observed in the experiments.

Synthesis and structural characterization of heavier group 1 methyl tetrazolate complexes: New bridging coordination modes of the tetrazolate ligand

A series of sodium, potassium, rubidium, and cesium complexes of methyl tetrazolate was prepared and structurally characterized. Treatment of methyl tetrazole (MetetzH) with the group 1 hydroxides in water at ambient temperature afforded Na(Metetz)(H 2O) 2 (92%), K(Metetz) (92%), Rb(Metetz) (97%), and Cs(Metetz) (97%) as colorless solids after workup. These complexes were characterized by spectral and analytical methods, thermogravimetric analysis, and by X-ray crystallography. Na(Metetz)(H 2O) 2 adopts a structure that consists of approximately octahedrally coordinated sodium ions that form infinite chains built up by two μ 2-aqua ligands and two μ 2- N 1, N 2-tetrazolate ligands between each sodium atom. The aqua ligand hydrogen atoms engage in hydrogen bonding with uncoordinated nitrogen atoms to hold the chains together. K(Metetz) and Rb(Metetz) are isostructural, with eight-coordinate metal ions and two metal–nitrogen bonds per nitrogen atom in each Metetz ligand. Cs(Metetz) has 10-coordinate cesium ions with two cesium–nitrogen bonds to two of the Metetz ligand nitrogen atoms and three cesium–nitrogen bonds to the other two nitrogen atoms. K(Metetz), Rb(Metetz), and Cs(Metetz) exhibit new coordination modes for the tetrazolate ligand.

Influence of the heavy fuel spill from the Prestige tanker wreckage in the overlying seawater column levels of copper, nickel and vanadium (NE Atlantic ocean)

The water column above the Prestige wreckage was sampled during two consecutive campaigns: Prestinaut (December 2002) two weeks after the tanker sunk and HidroPrestige0303 (March 2003) one month after the sealing of the main fuel leaks. Samples of the original cargo fuel and the emulsified fuel in the surface of the ocean were also collected. Analysis of the fuel indicated the release of 135 kg of Cu, 1700 kg of Ni and 5300 kg of V from the original fuel to the water column, remaining 35 kg of Cu, 3100 kg of Ni and 13,800 kg of V in the emulsified fuel. The metal partitioning between the water column and the emulsioned floating fuel, Cu > Ni ~ V, are in accordance with the stability index for the metal–nitrogen bond in metalloporphyrins. This release had an impact on dissolved trace metal concentrations in the water column. An increase on dissolved copper (2.8–4.7 nM) and nickel (2.2–8.0 nM) with respect to natural values (1–3 nM for Cu and 1.6–5 nM for Ni) was observed. Values for vanadium (28–35 nM) were in the range of pristine North Atlantic waters (30–36 nM). This contamination was especially observed in the upper water column (0–50 m), associated with the mixing of seawater with the fuel moving upwards, and in deep waters, where the residence time of fuel is higher. Future research in this field should focus on the environmental variables and the processes that control the release of contaminants from fuels for a better assessment of the contamination in oil-spill events.

Diamagnetic 8-amidoquinoline and 8-(trialkylsilylamido)quinoline complexes of divalent nickel and zinc

Transamination of Zn[N(SiMe 3) 2] 2 with 8-(triisopropylsilylamino) ( 1a) and 8-(tert-butyldimethylsilylamino)quinoline ( 1b) yields monomeric heteroleptic bis(trimethylsilyl)amido zinc 8-(trialkylsilylamido)quinoline ( 2a, 2b). The reaction of Zn[N(SiMe 3) 2] 2 with 8-aminoquinoline leads to the formation of heteroleptic dimeric 8-amidoquinoline zinc bis(trimethylsilyl)amide ( 3). This compound shows fluxionality on the NMR time scale due to a transannular trans– cis isomerization process and also a strong temperature dependency of the ratio of these two isomers. Variation of the stoichiometry allows the synthesis and isolation of homoleptic zinc bis(8-amidoquinoline) ( 4) with the zinc atoms in a distorted tetrahedral environment. The metallation of 8-aminoquinoline with (tmeda)NiMe 2 yields diamagnetic nickel bis(8-amidoquinoline) ( 5) with a nickel center showing a distorted square planar coordination sphere. Dinuclear zinc complexes are accessible employing tetra-dentate di(8-aminoquinolyl)diphenylsilane ( 6). The metallation of 6 with dimethylzinc yields dimeric zinc di(8-amidoquinolyl)diphenylsilane ( 7) with tetrahedrally coordinated zinc atoms. A comparison of the molecular structures of 1a, 2b, 3, 4, 5, 6, and 7 shows nearly no dependency of the structural data of the quinolyl unit on the substitution pattern of the amino function. The metal–nitrogen bond lengths depend on the coordination numbers of the metal and the nitrogen atoms (terminal or bridging position) as well as the electrostatic attraction between the metal cations and the amino bases.

Poly(germaniumpolycarbodiimides)

Poly(metalpolycarbodiimides) were obtained from cyanamide or dilithium cyanamide and di-, tri- or tetra-chlorogermanes by dehydrochlorination, transmetallation or exchange GeCl/GeN reactions. The preparation was extended to mesityldichlorostibane. Metal polyhalides develop a high tendency to generate poly(metalcarbodiimide) cryptands in spite of the linear molecular shape of the carbodiimide links. In these oligomeric structures, the reactivity of the metal nitrogen bond towards protic reagents is preserved and allows the confirmation of their structure by chemical investigations.

Dinitrogen Functionalization with Bis(cyclopentadienyl) Complexes of Zirconium and Hafnium

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Nitrogen–Carbon Bond Formation from N2 and CO2 Promoted by a Hafnocene Dinitrogen Complex Yields a Substituted Hydrazine

Nitrogen–Carbon Bond Formation from N₂ and CO₂ Promoted by a Hafnocene Dinitrogen Complex Yields a Substituted Hydrazine

Theoretical study of complexation of alkali metal ions in the cavity of arylazacrown ethers

Complexes of N-arylaza-15(18)-crown-5(6) ethers with K + and Na + are studied by the density functional method with and without regard for the specific solvation of the cation by water molecules in the macrocycle cavity. The effects of solvation on the stability of different complex conformers are studied through explicitly including up to four water molecules in the complex. Two types of conformations are considered, namely, the axial type characterized by the existence of a metal–nitrogen bond and the equatorial type, in which this bond is not formed. The selectivity of the arylaza-15(18)-crown-5(6) ethers for Na + and K + is estimated using the bonding energy. It is found that both azacrown ethers are selective for sodium, although interaction with water impairs the selectivity.

Bonding Properties Related with Chiral Discrimination in Dinuclear Metal Complexes of Group 10

AbstractA series of neutral dinuclear homo‐ and heterochiral complexes formed by hydrazine (a molecule with axial chirality), a metal atom of group 10 (Ni, Pd, Pt), and halogen atoms (F, Cl, Br, I) was studied by computational methods including density functional theory. In the optimized structures the heterochiral complexes were always found to be energetically favored. The chiral discrimination depends on the contributions coming from the metal atoms and the halogen anions attached to them. Moreover, the relative energies of the optimized complexes are correlated with the electronegativity of the metals and the halogens as well as with the relative distances of the bond critical points in the metal–nitrogen bonds. Also the smaller deviation of the ligand–metal–ligand angles from the ideal value of 90° corresponds to the heterochiral complexes. An analysis of the bonding properties reveals a complex mechanism for the behavior of the electron lone pairs of the nitrogen and halogen atoms. The electronic properties of the optimized complexes were studied by NBO (Natural Bond Orbital) and QTAIM (Quantum Theory of Atoms in Molecules) methods. An NBO analysis of the energy differences between the stabilizing energies related to the interactions between an electron lone pair of the coordinated nitrogen atom and the opposite M–X antibonding orbital explain the differences of the total energies between the diastereomeric heterochiral and homochiral complexes. The stabilizing energies have systematically more negative values in the heterochiral complexes; this can be interpreteted as a measure of the trans influence. Small energy values related to the cis influence were found mainly in the nickel complexes. The M–N bonds in the heterochiral complexes are more polar with a higher bond order than that in the homochiral ones, as shown by QTAIM methods. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Dinitrogen functionalization with bis(cyclopentadienyl) complexes of zirconium and hafnium

The rich chemistry of substituted bis(cyclopentadienyl)zirconium and hafnium complexes bearing side-on coordinated dinitrogen ligands is highlighted in this Perspective. Our studies in this area were initially motivated by the desire to understand side-on vs. end-on dinitrogen coordination in bimetallic zirconocene and hafnocene N2 compounds. In the cases where eta2,eta2-dinitrogen compounds were isolated, both structural and computational data have established significant imido character in the metal-nitrogen bonds. This additional bonding interaction, which is diminished in end-on complexes bearing both terminal and bridging N2 ligands, facilitates dinitrogen functionalization by non-polar reagents including dihydrogen, carbon-hydrogen bonds and weak Brønsted acids such as water and ethanol. In hafnocene chemistry, where unwanted side-on, end-on isomerization is suppressed, cycloaddition of phenylisocyanate to coordinated N2 has also been accomplished. For N-H bond forming reactions involving H2, kinetic measurements, in addition to isotopic labelling and computational studies, are consistent with dinitrogen functionalization by 1,2-addition involving a highly ordered, four-centred transition structure.

Complexation of Transition Metals by 3-Azidopropionitrile. An Electrospray Ionization Mass Spectrometry Study

Most complexes of azides and transition metals involve the N(3)(-) azide anion as a ligand other than an organic azide. Complexes of organic azides with metals are involved in biological applications and in the deposition of nitrenes on metal surfaces, producing nitride layers for semi-conductors preparation; this makes the study of these interactions an important issue. This work describes a study of the complexation of nickel and cobalt by 3-azidopropionitrile by means of electrospray ionization mass spectrometry (ESI-MS). Complexes were obtained from solutions of NiCl(2) and CoCl(2) in methanol/water. In the case of nickel, other NiX(2) salts were investigated (where X = Br or NO(3)) and other solvents were also studied (notably ethanol/water). All complexes detected were single positively charged, with various stoichiometries, some resulted from the fragmentation of the ligand, the loss of N(2), and HCN being quite common. The most abundant cations observed were [Ni(II)AzAzX](+), where X = Cl, Br, NO(3). Some of the complexes showed solvation with methanol/ethanol/water. Metal reduction was observed in complexes where a radical was lost, resulting from the homolytic cleavage of a metal-nitrogen bond. Collision induced dissociation (CID) experiments followed by tandem mass spectrometry (MS-MS) analysis were not absolutely conclusive about the coordination site. However, terminal ions observed from the fragmentation routes were explained by a proposed gas-phase mechanism. Density functional theory calculations were carried out and provided structures for some complexes, pointing to the possibility of 3-azidopropionitrile acting as a mono- or a bidentate ligand.

Nona-coordinated MO 6N 3 centers M = Zr, Hf as a stable building block for the construction of heterometallic alkoxide precursors

The modification of zirconium or hafnium alkoxides with diethanolamine, H 2dea, leads to the formation of unique nona-coordinated M{μ-η 3-NH(C 2H 4O) 2} 3 cores. The mechanism is used to develop a self-assembly approach to the first thermodynamically stable zirconium–titanium and hafnium–titanium precursors, Zr{μ-η 3-NH(C 2H 4O) 2} 3[Ti(O i Pr) 3] 2 ( 1) and Hf{μ-η 3-NH(C 2H 4O) 2} 3[Ti(O i Pr) 3] 2 ( 2). Mass spectrometric characterization of these compounds demonstrates their volatility. In addition to the solution stability of these compounds the volatility makes them attractive single source precursors for MOCVD and ALD applications. These precursors are also interesting candidates for application in sol–gel synthesis of microporous materials as the stability of the core prevents self-assembly of ligands on the outer surface of the primary particles formed during the hydrolysis. A n-propoxide analog of 1 can be prepared from zirconium n-propoxide but does not yield any crystalline material. It is demonstrated that 1 can be prepared from [Zr(O n Pr)(O i Pr) 3( i PrOH)] 2, however, with a lower yield compared to the use of zirconium isopropoxide. The single crystals obtained from systems containing zirconium isopropoxide, titanium isopropoxide and triethanolamine H 3tea turned out to be Ti 2(O i Pr) 2({μ-η 4-NH(C 2H 4O) 3} 2) 2 ( 4). Theoretical calculations indicate that the octacoordinate M{μ-η 4-N(C 2H 4O) 3} 2 core, anticipated in reaction with H 3tea, will have metal–nitrogen bonds that are too long for its stabilization. This explains why the formation of 4 is thermodynamically favored over the formation of heterometallic species.

Lewis acidity of group 14 tetrahalides in gas phase

Donor–acceptor complexes of silicon, germanium and tin tetrahalides with nitrogen-containing donors MX 4· nL (M=Si,Ge,Sn; X=F,Cl,Br; L=NH 3, Py, 2,2′bipy, 1,10-phen) have been theoretically studied at the B3LYP/DZP level of theory. It was found that some of the complexes possess negative Gibbs free energies, i.e. their decomposition into components is thermodynamically favorable. At the same time the formation of normal covalent (by means of the bond length) donor–acceptor bond was evidenced. Scanning of the potential energy surface (PES) revealed that such complexes are metastable species with barriers to dissociation 4–60 kJ mol −1. Energies of the element-nitrogen donor–acceptor bond are strongly dependent on the coordination polyhedron type; however, for the given type of the coordination polyhedron they are independent on the nature of the donor molecule (NH 3, Py, bipy, phen). It is shown that the reorganization energy of the acceptor molecule (36–280 kJ mol −1) governs the stability of the complexes. The reorganization energies of the donor molecules (1–32 kJ mol −1) are much smaller. Dissociation enthalpies of the complexes decrease in order Sn>Ge>Si, in line with increasing reorganization energy of the acceptor. At the same time, the donor–acceptor bond energy changes nonmonotonically: Ge<Si<Sn. The values of the gas phase dissociation enthalpy should not be used to estimate the metal-nitrogen bond energy. On the basis of theoretical studies, the most promising candidates for stable gaseous complexes of group 14 halides are complexes of tin tetrahalides with bidentate donor ligands, such as SnF 4phen.