Monodentate N-donor Ligand Research Articles

A homoleptic AgIII complex stabilized by succinimidate ligands.

Herein, the first example of a homoleptic AgIII complex stabilized by a monodentate N-donor ligand is presented. Na2[S2O8] oxidizes the linear AgI complex, Na[Ag(succ)2] (1Na), to form a square planar argentate(iii) ion, [Ag(succ)4]-, which crystallizes with a polymeric chain-structure, M[Ag(succ)4] (2M), when treated with alkali metal sulfate M2SO4 (M = K, Rb, Cs). A mixed-valent Robin-Day class I system, [(H2O)Ag][Ag(succ)4] (2Ag), forms in the absence of K+/Rb+/Cs+ ion. Diamagnetic 2Cs displays a succinimide C[double bond, length as m-dash]O stretching frequency at higher energy than does the isoelectronic PdII complex, [(H2O)Na]2[Pd(succ)4] (3Na). Moreover, 2Cs displays UV-vis absorptions that are more intense and occur at lower energy than those in 3Na. The electron-deficient nature of 2Cs is further evident from its ability to oxidize water to O2. From 109Ag magic-angle spinning NMR studies, a highly deshielded AgIII environment in 2Cs (2080 ppm) relative to the AgI starting material 1Na (492 ppm) is observed.

Single monodentate N-donor ligands versus multi-ligand analogues in Pd(II)-catalysed C–C coupling at reduced temperatures

Deployment of reduced operational temperatures is industrially beneficial and use of the highly efficient, phosphine-based precatalysts is limited by their high costs and inaccessible preparation procedures. In order to study of the influence of coordination environments on catalyst reactivities at reduced temperatures, design of palladium(II) complexes bearing single monodentate N-donor ligands was considered necessary. Consequently, dichloridopalladium(II) complexes of 2-(thiophen-2-yl)-1H-imidazole ligands (1–8), 2,4,5-triphenyloxazole (9) and 2-(1H-imidazol-2-yl)pyridine (10) have been prepared, structurally characterized and studied as N-stabilized precatalysts. Ligand donor strengths were spectroscopically estimated by protonation-deprotonation equilibria. The palladium(II) complexes were obtained in three coordination environments; (i) the mono-ligand complexes bearing trans-solvent co-ligands (PdL.acn and PdL.dmf), (ii) the chlorido-bridged dimers µ-(PdL)2 and (iii) the trans-bis-ligand PdL2 complexes. Considering ambient temperature operations, the catalysis outcomes obtained for the monodentate mono-ligand coordination designs represent an improvement in terms of temperature and reaction time relative to previously reported N-stabilized palladium precatalysts. The mono-ligand pre-catalysts efficiently generate living active palladium species from 40 °C while a trans-bis-ligand phosphine-based pre-catalyst analogue PdI2(PPh3)2 displayed no yield under the same temperature conditions. Trans-bis-ligand coordination is observed to utterly hinders catalyst efficiencies at the studied temperatures and preformed mono-ligand complexes of mono-dentate N-donors provided positive ligand effects while in situ catalyst generation failed. Therefore, the use of multiple ligand equivalents should be discouraged.

Selective detection of trinitrophenol by a Cd(ii)-based coordination compound.

A Cd(ii)-based coordination compound, [CdI2(4-nvp)2] (1), has been synthesized using CdI2 and monodentate N-donor ligand 4-(1-naphthylvinyl)pyridine (4-nvp). The solid-state supramolecular architecture has been characterized by X-ray crystallography. An acute thermal stability and excellent level of phase purity tempted us to use it for material applications. Interestingly, compound 1 exhibits a high selectivity towards trinitrophenol (TNP) in the presence of other nitroaromatics. Therefore, this material may be used for anti-terrorist activities in the detection of explosive materials as well as in the recognition of TNP in analytical laboratories.

Computational strategies to probe CH activation in dioxo-dicopper complexes.

We employ density functional theory and energy decomposition analysis to probe the mechanism of CH activation in dioxo-dicopper complexes. The electrophilicity of monodentate N-donor ligands coordinated to Cu is systematically varied to examine the response of barriers to the two proposed pathways - one-step oxo-insertion and two-step radical recombination. Electron-withdrawing ligand stabilize the oxo-insertion transition state via charge transfer interactions, and therefore lead to lower barriers. On the other hand, barriers to the CH activation step in the radical recombination mechanism exhibit almost no dependence on N-donor electrophilicity. Based on the similarities between calculated and experimental Hammett relationships, the oxo-insertion pathway appears to be the preferred mechanism of CH activation in dioxo-dicopper catalysts.

Structural influence of the substituent in carboxylate anion on example of α- and β-naphthoate complexes of Co(II), Ni(II), Cu(II), and Zn(II)

The results on the synthesis and study of the crystal structures of molecular complexes of transition metals with anions of α- and β-naphthoic acids and monodentate N-donor ligands (MeCN, 2,3-lutidine) are presented. The compositions and structures of the isolated complexes are determined by the following factors: steric hindrances, intermolecular interactions of the aromatic fragments, and the electronic structure of the metal center.

Bonding modes of nitrite and nitrate in palladium(II) and platinum(II) complexes

The crystal structures of the well-known complexes, [(Me4en)M(II)X2] (Me4en = N,N,N′,N′-tetramethylethylenediamine; M(II) = Pd(II) or Pt(II); X− = NO2− or NO3−) have been determined. For [(Me4en)Pd(NO2)2] and [(Me4en)Pt(NO2)2], the nitrite anion acts as a monodentate N-donor ligand in the solid state. In contrast, for [(Me4en)Pd(ONO2)(O2NO)], the two nitrate anions act as a monodentate O-donor (ONO2) and a bidentate O,O′-donor (O2NO). Recrystallization of [(Me4en)Pt(NO3)2] from Me2SO yields the Me2SO adduct with a monodentate O-donor nitrate and a counteranionic nitrate, [(Me4en)Pt(ONO2)(S-Me2SO)](NO3). The solution behavior of these complexes, including the equilibrium between coordinated and free Me2SO, has been investigated.

C−H Activation of Imines by Trimethylphosphine-Supported Iron Complexes and Their Reactivities

First examples of ortho-metalated mono-iron complexes of monodentate N-donor ligands via C−H activation have been synthesized. Treatment of benzylicimines and ketimines with Fe(CH3)2(PMe3)4 and Fe(PMe3)4 under mild conditions results in ortho-metalated hydrido-iron(II) and methyl-iron(II) complexes in high yields, and their iodomethane reactions give thermally stable iodo-iron(II) compounds, which are interesting versatile nucleophiles in organometallic and organic chemistry.

Molecular structure and catechol oxidase activity of a new copper(I) complex with sterically crowded monodentate N-donor ligand

The attempted alkylation of 1,3-bis(2'-pyridylimino)isoindoline (indH) by the use of n-BuLi and subsequent alkyl halides led to quaternization of the pyridine nitrogens and the zwitterionic monodentate N-ligand (Me(2)ind)I was formed. By the use of the ligand the copper(I) complex [Cu(I)(Me(2)ind)I(2)] was prepared and its structure determined. It was found to be good catalyst for the oxidation of 3,5-di-tert-butylcatechol (DTBCH(2)) to 3,5-di-tert-butyl-1,2-benzoquinone (DTBQ) and H(2)O(2) by dioxygen. Detailed kinetic studies revealed first-order dependence on the catalyst and dioxygen concentration and saturation type behavior with respect to the substrate.

Synthesis, Crystal Structure, Thermal Behavior and IR Characterization of Pentacarbonyl(4-methylpyridine)chromium(0) Complex

Pentacarbonyl(4-methylpyridine)chromium(0) complex was isolated from n-hexane solution as yellow plate-like crystals and characterized by using X-ray crystallography. It crystallizes in the orthorhombic system with the space group Cmcm and Z = 4. The unit cell parameters are a = 11.737(1) A, b = 12.857(2) A, c = 8.465(1) A. The single crystal X-ray structure of the complex shows that the coordination sphere around the chromium central atom is slightly distorted octahedron, involving the 4-methylpyridine (4-mp), ligand as a monodentate N-donor ligand and five carbonyl groups. The four equatorial CO groups in the complex, with the Cr–C2 distance of 1.886 Ǻ, are slightly bent away from the 4-methylpyridine ligand with the N–Cr–C2 angle of 91.69°. The pyridine ring plane makes an angle of 135.17° with the Cr–N–CO bond axis. The thermal analysis (differential thermal analysis and thermal gravimetry) and IR spectra of the complex indicated that the compound undergoes complete decomposition to form the Cr2O3 as the final decomposition product. The crystal structure of pentacarbonyl(4-methylpyridine)chromium(0) complex has been determined and its thermal behavior has also been studied.

Synthesis, Crystal and Molecular Structure of 2-Pyridylethanolbis(saccharinato)mercury(II)

2-Pyridylethanolbis(saccharinato)mercury(II), [Hg(sac) 2 (pyet)], where sac and pyet are the saccharinate anion and the 2-pyridylethanol molecule, respectively, crystallizes in the triclinic space group P1 (No. 2) with a = 10.4518(6), b = 11.3796(6) (5), c = 19.9945(12) A, a = 102.758(3)° β = 98.146(3)°, γ = 104.751(3)°, Z = 4, V = 2193.0(2) A 3 . The unit cell contains two crystallographically independent [Hg(sac) 2 (pyet)] units in which the mercury(II) ion is tetrahedrally coordinated by two nitrogen atoms of two sac ligands, and one nitrogen and one oxygen atoms of one neutral pyet ligands. The pyet acts as a bidentate N- and O-donor ligand forming a six-membered chelate ring, while sac behaves as a monodentate N-donor ligand. The average bite angle of the pyet ligand is 75.8(5)°. The Hg-N sac bond distances are in the range 2.0874(18) and 2.1931(18) A, whereas the Hg-N pyet and Hg-O pyet bond distances are 2.2452(19)-2.3202(19) and 2.6036(17)-2.5902(16) A, respectively. The crystal exhibits two strong hydrogen bonds between the hydroxyl O atom of pyet and sulfonyl O atoms of sac and the C-H...O type weak hydrogen bonds between H atoms of the aromatic rings of the pyet and the sulfonyl O atoms of the sac ligands. Furthermore, packing of the molecules in the solid-state results in aromatic π-π interactions associated with the aromatic rings of sac-sac and py-py.

Synthesis and Structure of Trans-bis(ethanolamine)bis(saccharinato)mercury(II)

Trans-bis(ethanolamine)bis(saccharinato)mercury(II), [Hg(ea)2(sac)2], where ea and sac denote the ethanolamine molecule and the saccharinate anion, respectively, crystallizes in the triclinic space group P (No. 2) with a = 9.4651 (5), b = 10.4365 (5), c = 11.9314 (6) Å, α = 84.402 (1)° β = 78.313 (1)°, γ = 75.307 (1)°, Z = 2, V = 1115.11 (10) Å3. The structure consists of isolated [Hg(ea)2(sac)2] units in which the Hg(II) ion is octahedrally coordinated by two nitrogen and two oxygen atoms of two neutral ea ligands, and two nitrogen atoms of two sac ligands. The ea acts as a bidentate N- and O-donor ligand and occupies the trans positions of the equatorial plane of the coordination octahedron forming a fivemembered chelate ring, while sac behaves as a monodentate N-donor ligand occupying the axial positions. The average Hg-Nsac and Hg-Nea bond distances are 2.739 (3) and 2.114 (7) Å, respectively. The crystal exhibits extensive hydrogen bonds between the hydroxyl and amine hydrogen atoms of the ea ligands and the sulfonyl, carbonyl and amine groups of the sac ligands.

Palladium (II) compounds containing mono- and bidentate primary ferrocenylamines. a study of the cyclopalladation of: [ (η 5-C 5H 5)Fe{ (η 5-C 5H 4)- (CH 2)n-NH 2}] (with n=1 or 2)

The reactions of palladium (II) salts with the primary ferrocenylamines: [ ( η 5-C 5H 5)Fe{ ( η 5-C 5H 4)- (CH 2) n -NH 2}] [with n=1 (1a) or 2 (1b)] are reported. These substrates react with Na 2 [PdCl 4] in methanol at room temperature giving: [Pd{ ( η 5-C 5H 5)Fe [ ( η 5-C 5H 4)- (CH 2) n -NH 2]} 2Cl 2] [with n=1 (2a) or 2 (2b)] with the ferrocenylamine acting as a monodentate N-donor ligand. However, when compounds 1 are treated with Pd (CH 3COO) 2 in toluene, followed by the addition of LiBr and the subsequent treatment of the solids formed with triphenylphosphine, the cyclopalladated complexes: [Pd{ ( η 5-C 5H 5)Fe [ ( η 5-C 5H 3)- (CH 2) n -NH 2]}Br (PPh 3)] [with n=1 (3a) or 2 (3b)] were obtained. NMR studies reveal that compounds 3 contain a five- (in 3a) or a six- (in 3b) membered metallacycle fused with the ferrocenyl unit.

Carboxylate-Bridged Diiron(II) Complexes: Synthesis, Characterization, and O2-Reactivity of Models for the Reduced Diiron Centers in Methane Monooxygenase and Ribonucleotide Reductase

Diiron(II) complexes with an oxygen-rich coordination environment were assembled with the dinucleating dicarboxylate ligands m-xylylenediamine bis(Kemp's triacid)imide (H2XDK) and the more soluble analogue m-xylylenediamine bis(propyl Kemp's triacid)imide (H2PXDK). X-ray crystallographic analysis revealed that, in most of the complexes, only one monodentate N-donor ligand is bound to each iron(II) ion. In addition to XDK and PXDK, a variety of other ligands bridge the dimetallic core including chloride, fluoride, triflate, or carboxylate. The tris(carboxylate-bridged) complexes [Fe2(μ-XDK)(μ-O2CPh)(ImH)2(O2CPh)(MeOH)] (3) and [Fe2(μ-O2CC(CH3)3)(μ-PXDK)(N-MeIm)2(O2CC(CH3)3)] (4) have the same ligand composition as the diiron(II) cores in the hydroxylase component of methane monooxygenase (MMO) and in the R2 protein of ribonucleotide reductase (RNR). The coordination environments of the two iron centers in 3 and 4 are inequivalent, with one iron being 6-coordinate and the other being 4-coordinate. The bridging benzoate and pivalate ligands have an unusual coordination mode with a Fe−O−C bond angle close to 180°. Fits of magnetic susceptibility data collected for several of the complexes between 300 and 4 K indicated that the two iron(II) centers are weakly antiferromagnetically coupled with a coupling constant which does not depend on the nature of the bridging ligands. Mössbauer spectra of polycrystalline and frozen THF solution samples of 4 exhibited two overlapping doublets of equal intensity, reflecting the different coordination environments of the two iron(II) ions. The nearly identical Mössbauer parameters for the solid and frozen solution samples indicate that the dinuclear core remains intact upon dissolution. Stopped-flow studies of the reaction of 3 and 4 with O2 in THF showed the rapid formation (kψ ≈ 74 s-1 for 3 at 202.5 K and kψ ≈ 300 s-1 for 4 at 197 K) of colored intermediates with broad absorption maxima near 660 and 670 nm, respectively. These values are characteristic of peroxo-to-iron charge-transfer bands and similar to that observed for the (μ-peroxo)diiron(III) intermediate (Hperoxo) in the MMO reaction cycle.

Synthesis and structural study of complexes of nickel(II) with 4-amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro-l,2,4-tria-zine

Bis-ligand nickel(II) complexes with 4-amino-2,6-dimethyl-5-oxo-3-thioxo-2,3,4,5-tetrahydro-1,2,4-tria-zine have been prepared by reaction between the triazine and the corresponding nickel salt in the 2:1 molar ratio, respectively. Conductance, magnetic, and infrared and visible spectroscopy data have been used for structural assignments. Pseudooctahedral structures are proposed for the complexes with the triazine molecule acting either as a monodentate N-donor ligand or a bidentate N- and S-donor ligand. An X-ray structural determination carried out with [Ni(triazine) 2(H 2O) 2](ClO 4) 2 shows that the triazine acts as a bidentate ligand via the 4-amino nitrogen and the 3-thioxo sulfur (Ni-S=2.377 Å; Ni-N=2.079 Å) and the two H 2O molecules complete the hexacoordination of nickel(II) (Ni-O=2.135 Å).

Olefin ligands: II. Syntheses of 2,6-diallylpyridine (DAP) complexes of iridium(I), ruthenium(II), palladium( II) and platinum(II); crystal structures of [RuCl 2(PPh 3)(DAP)] and [PdCl 2(DAP) 2

The tridentate ligand 2,6-diallylpyridine (DAP) has been used to synthesize novel complexes of iridium(I), ruthenium(II), palladium(II) and platinum(II) of formulae [Ir(COD)(DAP)][IrCl 2(COD)], [IrCl(CO)(DAP)], [Ir(COD)(DAP)]ClO 4, [RuCl 2(PPh 3)(DAP)],[PdCl 2(DAP) 2],[PtCl 2(DAP)]. All the complexes have been characterized by elemental analysis, IR, and 1H NMR spectroscopy. The molecular structures of [RuCl 2(PPh 3)(DAP)] and [PdCl 2(DAP) 2] have been determined by single-crystal X-ray diffraction studies. Crystals of the ruthenium complex are orthorhombic, space group Pbca, with Z = 8 in a unit cell of dimensions a 11.492(5), b 18.942(3), c 23.083(9) Å. Crystals of the palladium complex are triclinic, space group P 1 with Z = 1 in a unit cell of dimensions a 7.950(4), b 8.745(4), c 9.578(4) Å, α 113.02(3), β 90.75(3), γ 116.65(3)°. Both structures were solved by Patterson and Fourier methods and refined by blocked full-matrix least-squares to R = 0.0528 for 2742 observed reflections in the first complex and by full-matrix least-squares to R = 0.0252 for 1948 observed reflections in the second. In the octahedral ruthenium complex, DAP acts as a tridentate ligand adopting a mer configuration and the phosphine ligand is trans to the pyridinic nitrogen, while in the trans square-planar palladium complex DAP acts as a monodentate N-donor ligand.

Thermal properties of thiocyanatocopper(II) complexes with some monodentate N-donor ligands

The thermal decomposition of CuL2(KCS)2, where L = NH3, pyridine and its methyl- and halogenoderivates showed that variability in the chemical properties of ligands L manifeatates itself in the different extent of the chemical change of NCS ligands.

Tetraphenylborate tetra- and pentacoordinated Complexes of rhodium(I) with diolefins

The synthesis and properties of complexes of the [Rh(COD)L 2]BPh 4 type (COD = 1,5-cyclooctadiene, L = monodentate N-donor ligand) and of mixed complexes of the general formula [Rh(diolefin)L n ′L]BPh 4 (diolefin = COD or norbornadiene, L = monodentate N-donor ligand, L′ = P- or As-donor ligand, n = 1 or 2) are described. The stoichiometry of the precipitated complexes depends upon the nature of the diolefin and group Vb donor ligands.