Unsymmetrical Bidentate Research Articles

Highly Anisotropic Pd2Lab 2Lcc 2 and Pd2Lab 2Lcd 2 Type Cages by Heteromeric Completive Self-Sorting.

Pd(II)-based low-symmetry coordination cages possessing anisotropic cavities are of great interest. The common strategies employed to achieve such cages utilize either more than one type of symmetrical ligands (e.g., Laa, Lbb etc.) or only one type of unsymmetrical ligand (e.g., Lab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., Lab and Lcd, aiming at a low-symmetry Pd2Lab 2Lcd 2-type cage. It was accomplished by high-fidelity integrative self-sorting of two different low-symmetry cages having Pd2Lab 4 and Pd4Lcd 8-type architectures (homoleptic complexes of the designed ligands). Structural constraints and geometry complementarity in the ligand design drive the non-statistical exclusive self-assembly of the Pd2Lab 2Lcd 2-type cage. By taking advantage of the complemental geometries between ligands, a low-symmetry Pd2Lab 2Lcc 2-type cage was also obtained. Heteromeric completive self-sorting of three homoleptic assemblies (Pd2Lab 4, Pd4Lcc 8 and Pd4Lcd 8-type cages) into an exclusive mixture of Pd2Lab 2Lcd 2 and Pd2Lab 2Lcc 2-type mixed ligated assemblies was demonstrated through cage-to-cage transformations.

Highly Anisotropic Pd2Lab2Lcc2 and Pd2Lab2Lcd2 Type Cages by Heteromeric Completive Self‐Sorting

AbstractPd(II)‐based low‐symmetry coordination cages possessing anisotropic cavities are of great interest. The common strategies employed to achieve such cages utilize either more than one type of symmetrical ligands (e.g., Laa, Lbb etc.) or only one type of unsymmetrical ligand (e.g., Lab). To significantly enhance the anisotropy, we have designed two unsymmetrical bidentate ligands i.e., Lab and Lcd, aiming at a low‐symmetry Pd2Lab2Lcd2‐type cage. It was accomplished by high‐fidelity integrative self‐sorting of two different low‐symmetry cages having Pd2Lab4 and Pd4Lcd8‐type architectures (homoleptic complexes of the designed ligands). Structural constraints and geometry complementarity in the ligand design drive the non‐statistical exclusive self‐assembly of the Pd2Lab2Lcd2‐type cage. By taking advantage of the complemental geometries between ligands, a low‐symmetry Pd2Lab2Lcc2‐type cage was also obtained. Heteromeric completive self‐sorting of three homoleptic assemblies (Pd2Lab4, Pd4Lcc8 and Pd4Lcd8‐type cages) into an exclusive mixture of Pd2Lab2Lcd2 and Pd2Lab2Lcc2‐type mixed ligated assemblies was demonstrated through cage‐to‐cage transformations.

Synthesis, structure, and magnetic properties of lanthanide(III) complexes incorporating a tris-chelate cobalt(III) complex as a metalloligand

A series of CoIII–LnIII–CoIII trinuclear complexes [Ln{Co(Hmtimn)3}2](NO3)3 were prepared by following a simple one-pot synthesis method, mixing an unsymmetrical bidentate ligand 2-(2-imidazolinyl)-6-methoxypheol (H2mtimn) with Co(NO3)2·6H2O and LnX3· 6H2O (where Ln = La, Ce, Pr, Nd, Gd or Dy and X = NO3 − or Cl−) in methanolic solution in the presence of triethylamine in air. In the reaction mixture, this leads to the in situ formation of a tris-chelate CoIII metalloligand unit, which can coordinate LnIII ions through the interactions of phenolato- and methoxy-O donors. X-ray structural analysis revealed that the CoIII metalloligand functions as a rigid tripodal ligand to coordinate to a LnIII ion by six oxygen donors. The two metalloligands in the complex exhibit homochiral aggregation (ΔΔ or ΛΛ) upon coordination to the LnIII ion. The coordination of the central LnIII ion was found to be a distorted icosahedral geometry. Magnetic susceptibility measurements reveal that both cobalt and central lanthanide ions exist in trivalent states.

3,5-Bis(4-pyridyl)-1,2,4-oxadiazole: An Unsymmetric Bidentate Ligand, Polymeric Silver Complex and Antimicrobial Activity Study

1,2,4-Oxadiazole based unsymmetric bidentate ligand, 3,5-bis-(4-pyridyl)-1,2,4-oxadiazole has been employed for complexation with silver nitrate; this ligand has been used for the first time for preparation of any coordination complex. A polymeric array of one-dimensional silver-ligand complex is formed where each metal ion is coordinated to two 4-pyridyl groups of two different ligands and two O-atoms of a nitrate ion. Single crystal X-ray data shows presence of hydrogen bonding and π-π stacking between each one-dimensional array which leads to formation of channels in its solid state. The hydrogen bonding interactions have also been verified by Hirsfeld surface analysis plots. Antimicrobial property study of ligand 3,5-bis-(4-pyridyl)-1,2,4-oxadiazole has been performed with Lactobacillus plantarum and it inhibits the growth at 12.5 μg mL-1.

Coordination driven self-assembled 18-component molecular octahedron

Unsymmetric bidentate ligands offer multiple binding modes with respect to the orientations of the coordinating sites, the unsymmetric nature of ligand 3,5-bis(3-pyridyl)-1,2,4-oxadiazole, L1 arises because of orientations of 3-pyridyl groups with respect to central 1,24-oxadiazole ring. Ligand L1 forms a discrete molecular octahedron [Pd6(L1)12](NO3)12, 1 when combined with Pd(NO3)2 in DMSO where the bound ligands are in cisoid-up orientation. In cage 1, Pd(II) ions are present at the vertices of the octahedron whereas twelve ligands are present at its edges, the opposite Pd-Pd distance in compound 1 is 17.501 Å. 1H NMR and DLS study of compound 1 with different guests reveals that resorcinol has interaction with the cage.

Novel Zn- and Cd-Schiff base complexes as the potent anticancer agents: Synthesis, spectral characterization and theoretical study

A novel unsymmetrical bidentate Schiff base ligand and its complexes, with the common formula of MLX2 (M(II) = Zn(II) and Cd(II); X− = Cl−, Br− and I−), using a reaction between 1,2-diaminobenzene and (E)-3-(4-(Dimethylamino) phenyl) acrylaldehyde were successfully synthesized. The structure of all the as-made compounds was identified by techniques including 1H NMR,13C NMR, ESI-mass, FT-IR, UV–Vis, melting point and molar conductivity. The analytical and spectral data confirmed the metal to ligand ratio of 1:1 in the Zn(II) and Cd(II) complexes. The anticancer activity of the compounds on cancer cells was investigated on HCT116 cell line, where the MTT method was used to screen cytotoxicity effects. The flow cytometry method also was used to determine the mechanism of cell death. Our data reveal that CdLCl2 can block the cell cycle and induction apoptosis. In addition, using Gaussian 16 program, the structure of the samples was optimized, and some important properties such as enthalpy change, entropy change and total energy were extracted. The molecular electrostatic potential, nonlinear optical properties, natural bond orbital and frontier molecular orbitals analysis were calculated for all compounds. Further, the electrophilic and nucleophilic sites, energy gap, ionization potential, electron affinity, natural population analysis and natural atomic orbitals were studied.

Slow Magnetic Relaxation in Cobalt(II) Complexes with One-Dimensional Hydrogen-Bonded Networks

Two new cobalt(II) complexes with an unsymmetrical bidentate ligand, 2-(1,4,5,6-tetrahydropyrimidin-2-yl)-6-methoxyphenol (H2mthp), were synthesized and crystallographically characterized. Tetra- and hexa-coordinate mononuclear complexes were selectively obtained by adjusting the stoichiometry of the base. The coordination geometry of hexa-coordinated complex was severely distorted from an ideal octahedron, due to the NO5 coordination environment from the mixed coordination of one Hmthp− and two H2mthp ligands. Both complexes formed one-dimensional chain networks by hydrogen-bond and N-H···π interactions. Single-molecule magnet behavior was observed for the tetrahedral complex under zero magnetic field. The relatively short Co···Co distances induced non-zero intermolecular magnetic coupling, which split the ground ±Ms levels to suppress quantum-tunneling of magnetization. In the octahedral complex, by contrast, the distance was not short enough to induce the coupling. As a consequence, single-molecule magnetic behavior was observed for the octahedral complex only in the presence of an external static field.

Solvent-dependent fac/mer-isomerization and self-assembly of triply helical complexes bearing a pivot part.

Tris–chelate metal complexes of unsymmetrical bidentate ligands can form two geometric stereoisomers, facial (fac) and meridional (mer) isomers. Due to the small difference in their properties, the highly-selective synthesis of one of the isomers is challenging. We now designed a series of tripodal ligands with a tris(3-(2-(methyleneoxy)ethoxy)phenyl)methane pivot. Surprisingly, the ratio of the fac/mer isomers of the triply helical FeII complexes significantly changed depending on the solvents. To the best of our knowledge, this is the first example of fac/mer isomerism of a labile tris(2,2′-bipyridine) FeII complex governed by the solvent. Furthermore, well-defined self-assemblies were quantitatively produced by imine bond formation with a suitable diamine. The supramolecular assemblies contained only the fac isomer even though a mixture of the two isomers existed in solution before the condensation reaction. Namely, the self-assembly formation effectively adjusted the geometries of the building unit that results in the suitable supramolecular structure.

Azido derivatives of dinuclear copper(II) and 1D polynuclear nickel(II) complexes containing an unsymmetrical bidentate amine: synthesis, crystalline architecture, and magnetic behavior

Dinuclear copper(II) complex [Cu2(L)2(μ2-1,1-N3)2(N3)2] (1) with double μ1,1-azido bridges and polynuclear nickel(II) complex [Ni(L)(μ2-1,1-N3)(μ2-1,3-N3)]n (2) with alternate double μ1,1-azido and μ1,3-azido bridges [L = 1-amino-2-(dimethylamino)ethane, N 3 − = azide ion] have been synthesized and were characterized by physicochemical and spectroscopic methods. X-ray structural analysis revealed that each Cu(II) center of 1 adopts a distorted square-pyramidal geometry with a CuN5 chromophore ligated through two N atoms of L, two N atoms of double bridging (μ1,1-N3), and one N atom of terminal azide ion. On the other hand, each Ni(II) center around the asymmetric unit of 2 adopts a distorted octahedral geometry with a NiN6 chromophore ligated through two N atoms of L, two N atoms of double μ1,1-N3, and two N atoms of double μ1,3-N3 bridges. The adjacent nickel centers are connected to alternate double μ1,1-N3 and double μ1,3-N3 bridges, affording a one-dimensional (1D) polymeric chain structure. Temperature-dependent magnetic susceptibility measurements evidenced a dominant antiferromagnetic interaction between the metal centers of both complexes 1 and 2.

Low-Symmetry Self-Assembled Coordination Complexes with Exclusive Diastereoselectivity: Experimental and Computational Studies.

A pyridine/aniline appended unsymmetrical bidentate ligand N-(4-(4-aminobenzyl)phenyl)nicotinamide, investigated in this work has two well-separated coordination sites. Combination of the ligand with cis-protected palladium(II) (i.e., PdL') and palladium(II) in separate reactions produced the corresponding Pd2L'2Lun2 and extremely rare Pd2Lun4 type self-assembled binuclear complexes, respectively. Notably, both varieties of complexes are prepared from a common ligand system. Two diastereomers (i.e., (2,0) and (1,1)-forms) are possible for Pd2L'2Lun2 type complex, whereas four diastereomers (i.e., (4,0), (3,1), trans(2,2), and cis(2,2)-forms) can be imagined for the Pd2Lun4 type complex. However, exclusive diastereoselectivity was observed, and the complexes formed belong to (1,1)-Pd2L'2Lun2 and cis(2,2)-Pd2Lun4 forms. The diastereomers are predicted from NMR study in solution and DFT calculations in gas-phase and implicit-solvent media; however, single-crystal structures of both the complexes provided unambiguous support. The rare Pd2Lun4 type complex is studied in further detail. Parameters like counteranion, concentration, temperature, and stoichiometry of metal to ligand did not influence the diastereoselectivity in complex formation. DFT calculations show the cis(2,2) form to be the most stable, followed by the (3,1) isomer. The lowest conformational strain in the bound ligand strands in the cis(2,2)-arrangement along with optimal intermolecular interactions makes it the energetically most stable of all the isomers. Molecular dynamics (MD) simulations were carried out to visualize the self-assembly process toward the formation of Pd2Lun4 type complex and the free energy difference between the cis(2,2) and (3,1) isomers. Snapshots of MD simulation elucidate the step-by-step progress of complexation leading to the cis(2,2)-isomer.

Synthesis of Unsymmetrical Bis(phosphine) Oxides and Their Phosphines via Secondary Phosphine Oxide Precursors

The unsymmetrical bidentate phosphine ligands (Me)2PCH2CH2CH2P(Et)2 (14), (Me)2PCH2CH2CH2P(iPr)2 (15), (Me)2PCH2CH2CH2P(Cy)2 (16), and (Me)2PCH2CH2CH2P(Ph)2 (17) were synthesized using air–stable phosphine oxide intermediates. In the first step, sodium phosphinites formed by deprotonation of (Me)2P(O)H, (Et)2P(O)H, and (iPr)2P(O)H were alkylated by 1-bromo-3-chloropropane. The different substitution rates of the chloride and bromide groups allowed the isolation of the intermediates (Me)2P(O)CH2CH2CH2Cl (2), (Et)2P(O)CH2CH2CH2Cl (3), and (iPr)2P(O)CH2CH2CH2Cl (4). Subsequent reaction of (Me)2P(O)CH2CH2CH2Cl (2) with the sodium phosphinites generated from (Et)2P(O)H, (iPr)2P(O)H, (tBu)2P(O)H, (Cy)2P(O)H, or (Ph)2P(O)H gave unsymmetrical bidentate phosphine oxides; reduction of these oxides yielded the unsymmetrical phosphines. The unsymmetrical bidentate phosphines react with metal salts to form complexes. X-ray crystal structures of cis-Pt((Me)2P(CH2CH2CH2)P(iPr)2)Cl2 (20) and racemic [CuI((Me)2P(CH2CH2CH2)P(Ph)2)]Cl (21) were obtained. The kinetics and scope of the synthetic route were also explored. Experiments showed that the rate of substitution of the alkyl chloride group in (R)2P(O)CH2CH2CH2Cl-type oxides increases relative to unsubstituted alkyl chlorides due to the presence of the phosphonyl group on one end of the molecule. The scope of the reaction involving 1,2-dihaloalkanes was also investigated, and it was found that the reaction mixture of sodium dimethylphosphinite and 1,2-dihaloalkanes formed tetramethylbis(phosphine) monoxide (22), which decomposes on work-up to give complex reaction mixtures.

Crystal structures and antibacterial properties of Cu(II) complexes containing an unsymmetrical N2O Schiff base ligand and bidentate N-donor heterocyclic co-ligands

Three new Cu(II) Schiff base complexes with bidentate N-donor heterocyclic co-ligands, 2,2'-bipyridine (1), 1,10-phenanthroline (2), and 2,9-dimethyl-1,10-phenanthroline (3), were synthesized and characterized by FT-IR and UV-vis spectroscopy. Molecular structures of [C20H21CuN4O](ClO4) (1) and [C24H25CuN4O](ClO4) (3) were characterized by single-crystal X-ray crystallography. The Schiff base ligand is an N2O-type ligand, which is the mono-condensed form of the reaction between 1,3-propanediamine and salicylaldehyde. The antibacterial activities of these complexes were investigated against one gram positive and four gram negative bacteria. Considerable antibacterial activity was obtained against both gram type bacteria. Complexes 2 and 3 with 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline, respectively, showed better antibacterial activity compared to 1 which has the 2,2'-bipyridine co-ligand.

Solid‐state and Computational Study of “Venus fly‐trap” Geometric Parameters for 1,5‐Cyclooctadiene in PdII and PtII β‐Enaminonato Complexes

The cod ligand (cis,cis‐1,5‐cyclooctadiene) can be superficially considered to mimic similarities in spatial behavior of a leaf of the Venus fly‐trap (Dionaea muscipula). Thus, the synthesis of an unsymmetrical bidentate trans ligand (N,O‐donor atoms) based on the β‐enaminonate backbone is introduced to evaluate the electronic and steric influence on the structural behavior of the cod ligand when coordinated to a square planar transition metal. A range of platinum(II) / palladium(II) complexes of the type [M(cod)(N,O‐Bid)]A (M = PtII, PdII; β‐enaminonato ligand (N,O‐Bid) = NH‐acac, NMe‐acac, NPh‐acac; A = BF4–, PF6–) is reported. The complexes were fully characterized, including by detailed X‐ray structural investigations. Theoretical calculations on the [M(cod)(N,O‐Bid)]+ complexes for the complete nickel triad are also described and the structural behavior of the cod ligand critically evaluated. The influence of the variation of the β‐enaminonato ligands on the coordination arrangement of the cod was investigated and found that no significant changes to the M–C and C=C bond lengths were observed. The Venus fly‐trap jaw angle (ψ), however, varies by ca. 8° and the twist angle (τ) by ca. 10°, whereas the cod bite angle (χ), as well as the β‐enaminonato ligand bite angle (N–M–O; θ) both remain virtually constant. Calculated spectroscopic tendencies within the Ni‐triad are also included.

Unsymmetrical bidentate ligands as a basis for construction of ambidentate ligands for functional materials: Properties of 4,4-dimethyl-1-phenylpentane-1,3-dionate

To establish a background to the possible use of its ambidentate derivatives as stimulus-responsive ligands in functional complexes, the basic coordination chemistry of the anion derived from 4,4-dimethyl-1-phenylpentane-1,3-dione (benzoylpivaloylmethane, bpmH) has been re-examined with selected main group and transition metal M(II) and M(III) species. There is evidence that the steric bulk of the 1,3-dione substituents is not sufficient to prevent oligomerisation of the Ni(II) complex and equilibrium mixtures of geometric isomers can be detected in solution for at least the Al(III), Co(III) and Pd(II) complexes. Crystal structure determinations on both [Cu(bpm)2] and [Pd(bpm)2] show, however, that a single isomer can be isolated in the solid state.

Hydrogen-Bonded Supramolecular Structures of Cobalt(III) Complexes with Unsymmetrical Bidentate Ligands: mer/fac Interconversion Induced by Hydrogen-Bonding Interactions

Cobalt(III) complexes with three unsymmetrical bidentate ligands containing a noncoordinating N–H bond and a phenolate-O donor as hydrogen-bond donor and acceptor, respectively, were prepared and characterized. 1H NMR spectroscopy indicated that all the tris-chelate Co(III) complexes prepared favor the mer configuration in solution. [Co(Hthp)3] and [Co(Himn)3] also possess the mer configuration in the crystals (Hthp– = 2-(1,4,5,6-tetrahydropyrimidin-2-yl)phenolate, Himn– = 2-(2-imidazolinyl)phenolate). On the other hand, [Co(Himl)3] takes the fac configuration in the crystal (Himl– = 2-(2-imidazolyl)phenolate). These Co(III) complexes showed three types of characteristic supramolecular structures: ladder, distorted hexagonal sheet, and honeycomb sheet structure, constructed by intermolecular hydrogen bonds. Heating [Co(Himn)3] and [Co(Himl)3] in methanol selectively afforded precipitates of the fac isomer due to the low solubility of the hydrogen-bonded supramolecular structures. This mer to fac isomeriza...

Crystal structure of bis-(benzoato-κO)di-butyl-tin(IV), nBu2Sn(bzo)2.

The title compound, [Sn(C4H9)2(C6H5COO)2], was synthesized in order to study the inter-action between di-n-butyl-tin(IV) oxide and some carb-oxy-lic acids. Di-n-butyl-tin(IV) dibenzoate, nBu2Sn(obz)2, exhibits the same structural features as other diorganotin(IV) dibenzoates characterized by an unsymmetrical bidentate bonding mode [Δ(Sn-O) ≃ 0.4 Å] of the two benzoate groups to tin. In a first approximation, the coordination sphere at tin resulting from the two stronger bonded O atoms [2.1227 (17) and 2.1405 (16) Å] and the two α-C atoms of the n-butyl groups [2.125 (3) and 2.129 (2) Å] is compressed to a tetra-gonal disphenoid [〈(C-Sn-C) = 148.2 (1)° and 〈(O-Sn-O) = 82.01 (6)°]. This coordination sphere is expanded by the less strongly bonded two O atoms [2.507 (2) and 2.485 (2) Å] to a substanti-ally distorted octa-hedron and by a weak inter-molecular Sn⋯O inter-action [2.943 (2) Å] to a penta-gonal bipyramid with the formation of centrosymmetric dimers. The unbranched butyl groups adopt two different conformations: anti-gauche [torsion angles: 166.0 (2)-63.9 (4)°] and gauche-gauche [65.0 (3)-56.3 (3)°]. Inter-molecular inter-actions between the dimers are restricted to O⋯H-C contacts (2.64 Å) and van der Waals inter-actions.

Low coordinate iron derivatives stabilized by a β-diketiminate mimic. Synthesis and coordination chemistry of enamidophosphinimine scaffolds to generate diiron dinitrogen complexes.

In an effort to mimic N-diaryl-β-diketiminate ligands (Nacnac), we have converted N-arylimine phosphine ligands to enamine-phosphinimines via the Staudinger reaction. By varying the aryl azide, one can access enamine-phosphinimine ligands with the same or different N-aryl substituents on both the enamine and phosphinimine units, which allows this intrinsically unsymmetrical bidentate donor set to present variable steric effects at the metal center. The enamine-phosphinimine was deprotonated and used in metathetical reactions with Fe(ii) bromide precursors to generate low coordinate complexes of the empirical formula [(CY5)NpN(Ar,Ar')]FeBr (where CY5 = cyclopentenyl; Ar,Ar' = 2,6-diisopropylphenyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl). Depending on the substituents, these bromide derivatives can be monomeric or dimeric via bromide bridges. Reduction under dinitrogen using potassium graphite generates the dinitrogen complexes ([(CY5)NpN(Ar,Ar')]Fe)2(μ-N2) for Ar,Ar' = 2,6-diisopropylphenyl, and Ar = 2,6-dimethylphenyl, Ar' = 2,4,6-trimethylphenyl. However, for the former, a unsymmetrical side product can be isolated that has a bridging N-2,6-diisopropylphenylimide unit with one enamido-phosphine ligand bound to one iron and the other iron stabilized with an intact enamido-phosphinimine. When the steric bulk is reduced on both nitrogen donors, a complicated product mixture is obtained after reduction from which a small amount of [(CY5)NpN(Ar,Ar')]Fe[(CY5)NP(Ar)] (Ar,Ar' = 2,6-dimethylphenyl) could be isolated. All of these complexes are paramagnetic and have been characterized by elemental analysis, magnetic studies and X-ray crystallography.

Novel nickel(II) and manganese(III) complexes with bidentate Schiff-base ligand: synthesis, spectral, thermogravimetry, electrochemical and electrocatalytical properties

An unsymmetrical bidentate Schiff base ligand, ethane 2-(4-methoxyphenyl)-1-iminosalicylidene, and its novel two mononuclear complexes, Nickel(II) [Ni(II)-2L] and Manganese(III) [Mn(III)Cl-2L] where L represents the ligand, have been synthesized and characterized by various physicochemical methods. The Ni(II) ion is coordinated by two nitrogen and two oxygen atoms with both the bidentate Schiff base ligands in an approximately square planar coordination geometry, while the manganese complex, the Mn(III) ion, is involved in an additional contact with one chloride anion for which the coordination sphere appears as a square pyramidal arrangement. The thermogravimetric analyses of the synthesized compounds revealed three different stages of decomposition for NONO bis-bidentate manganese and nickel complexes. The cyclic voltammetry studies of these complexes in N,N-dimethylformamide showed a redox couple for each one of them, such as Ni(II)/Ni(I) and Mn(III)/Mn(II), which are quasi-reversible. Their catalytic behaviors were tested showing that the nickel complex is an effective electrocatalyst in the reduction of bromocyclopentane. Regarding the manganese complex, it was revealed that it is an efficient catalyst in the activation of molecular dioxygen, currently applied in oxidation reactions of hydrocarbons according to the monooxygenase enzymes as those of cytochrome P450 model.

31P{1H}NMR and carbonyl force constants of unsymmetrical bidentate phosphine complexes of group (VI) metal carbonyls

In our present work we report synthesis of an unsymmetrical diphos ligand, 1-diphenylphosphino-2-di-m-tolylphosphinoethane and its coordinate complexes with group (VI) metal carbonyls such as Cr(CO)6 Mo(CO)6 and W(CO)6. The synthesized ligand and its complexes have been completely characterized by elemental analyses, FTIR, 1HNMR, 31P{1H}NMR and FAB mass spectrometry methods. Special emphasis has been given to calculations of carbonyl force constants. Based on the spectroscopic evidences it has been confirmed that these metal carbonyl complexes with the ditertiary phosphine ligand showed cis geometry in their molecular structure.

Reversible Intramolecular Cyclization in Ruthenium Complexes Induced by Ligand-centered One-electron Transfer on Bidentate Naphthyridine: An Important Intermediate for Both Metal– and Organo–Hydride Species

Abstract Two types of dicarbonylruthenium(II) complexes bearing the unsymmetrical bidentate ligand 2-(2-pyridyl)-1,8-naphthyridine were prepared. The complexes undergo irreversible ligand-localized one-electron reduction to form redox-induced metallacyclization between the bidentate naphthyridyl ligand and the terminal CO ligand located nearby. Chemical reductions using NaBH4 were also performed to isolate the reaction products; the formation of both a metal–hydride (Ru–H) and an organo–hydride (C–H) species was confirmed.