Embryotoxicity studies of tri‐n‐butyltin(IV) complexes of 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoic acid and 2‐[(E)‐2‐(3‐formyl‐4‐hydroxyphenyl)‐1‐diazenyl] benzoic acid on sea urchin development

The toxicity studies of free 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoic acid and 2‐[(E)‐2‐(3‐formyl‐4‐hydroxyphenyl)‐1‐diazenyl]benzoic acid and their tri‐n‐butyltin(IV) complexes were evaluated by using sea urchin early developmental stages as recommended model organisms for toxicity tests. The novel complexes, as the parent tri‐n‐butyltin(IV) chloride (TBTCl), caused mitosis block and induced high embryonic mortality in sea urchin. Copyright © 2005 John Wiley & Sons, Ltd.     

Four novel lanthanide complexes with 4‐ethylbenzoic acid and 5,5′‐dimethy‐2,2′‐bipyridine: Structures,luminescent, thermal properties and bacteriostatic activities

Four new lanthanide complexes [Ln(4‐EBA)₃(5,5′‐DM‐2,2′‐bipy)]₂·2C₂H₅OH (Ln = Ho ( 1 ), Tb ( 2 ), Er ( 3 )); [Ln(4‐EBA)₃(4‐EBAH)(5,5′‐DM‐2,2′‐bipy)]₂ (Ln = Eu( 4 ); 4‐EBA =4‐ethylbenzoate; 5,5′‐DM‐2,2′‐bipy =5,5′‐dimethy‐2,2′‐bipyridine; 4‐EBAH = 4‐ethylbenzoic acid) have been synthesized and characterized by elemental analysis and IR spectra. The single crystal results reveal that complexes 1 – 3 are isostructural. It is worth noting that the mole ratios of the carboxylate ligands and neutral ligands is 4:1 in complex 4 , which is different from the former and has been rarely reported. Nevertheless, all complexes are connected to form 1D chain by π ···π wake staking interactions. Additionally, the complexes 2 (Tb(III)) and 4 (Eu(III)) exhibit characteristic luminescent properties, indicating that ligands can be used as sensitizing chromophore in these systems. The thermal decomposition mechanism of the complexes has been investigated by TG/DSC–FTIR technology. Stacked plots of the FTIR spectra of the evolved gases show complexes broken down into H₂O, CO₂, and other gaseous molecules as well as the gaseous organic fragments. The studies on bacteriostatic activities of complexes show that four complexes have good bacteriostatic activities against Candida albicans but no bacteriostatic activity on Escherichia coli , and Staphylococcus aureus . Additionally, the complexes 1 to 3 have better bacteriostatic activities on Candida albicans than complex 4 .     

Antibacterial Activities and Nuclease Properties of Two New Ternary Copper(II) Complexes with 2‐(4′‐Thiazolyl)‐benzimidazole and 2,2′‐Bipyridine/1,10‐phenanthroline

Two new complexes: [Cu(TBZ)(bipy)Cl]Cl·H₂O ( 1 ) and [Cu(TBZ)(phen)Cl]Cl·H₂O ( 2 ) [TBZ=2‐(4′‐thiazolyl)‐ benzimidazole, phen=1,10‐phenanthroline and bipy=2,2′‐bipyridine] have been synthesized and characterized by elemental analysis, molar conductivity, IR, and UV‐vis methods. Complex 2 , structurally characterized by single‐crystal X‐ray crystallography, crystallizes in the monoclinic space group P2₁/c in a unit cell of a=0.85257(12) nm, b=2.5358(4) nm, c=1.15151(13) nm, β=118.721(8)°, V=2.183.2(5) nm³, Z=4, D_c=1.624 g·cm⁻³, µ=1.367 mm⁻¹. The complexes, free ligands and chloride copper(II) salt were each tested for their ability to inhibit the growth of two gram‐positive (B. subtilis and S. aureus) and two gram‐negative (Salmonella and E. coli) bacteria. The complexes showed good antibacterial activities against the microorganisms. The interaction between the complexes and calf thymus DNA in aqueous solution was investigated adopting electronic absorption spectroscopy, fluorescence spectroscopy, viscosity measurements and cyclic voltammetry. Results suggest that the two complexes can bind to DNA by intercalative mode. In addition, the result of agarose gel electrophoresis suggested that the complexes can cleave the plasmid DNA at physiological pH and room temperature. Mechanistic studies with different inhibiting reagents reveal that hydroxyl radicals, and a singlet oxygen‐like copper‐oxo species are all involved in the DNA scission process mediated by the complexes.     

Synthesis and structures of photoactive rhenium carbonyl complexes derived from 2‐(pyridin‐2‐yl)‐1,3‐benzothiazole, 2‐(quinolin‐2‐yl)‐1,3‐benzothiazole and 1,10‐phenanthroline

Carbon monoxide (CO) has recently been identified as a gaseous signaling molecule that exerts various salutary effects in mammalian pathophysiology. Photoactive metal carbonyl complexes (photoCORMs) are ideal exogenous candidates for more controllable and site‐specific CO delivery compared to gaseous CO. Along this line, our group has been engaged for the past few years in developing group‐7‐based photoCORMs towards the efficient eradication of various malignant cells. Moreover, several such complexes can be tracked within cancerous cells by virtue of their luminescence. The inherent luminecscent nature of some photoCORMs and the change in emission wavelength upon CO release also provide a covenient means to track the entry of the prodrug and, in some cases, both the entry and CO release from the prodrug. In continuation of the research circumscribing the development of trackable photoCORMs and also to graft such molecules covalently to conventional delivery vehicles, we report herein the synthesis and structures of three rhenium carbonyl complexes, namely, fac‐tricarbonyl[2‐(pyridin‐2‐yl)‐1,3‐benzothiazole‐κ²N ,N ′](4‐vinylpyridine‐κN )rhenium(I) trifluoromethanesulfonate, [Re(C₇H₇N)(C₁₂H₈N₂S)(CO)₃](CF₃SO₃), ( 1 ), fac‐tricarbonyl[2‐(quinolin‐2‐yl)‐1,3‐benzothiazole‐κ²N ,N ′](4‐vinylpyridine‐κN )rhenium(I) trifluoromethanesulfonate, [Re(C₇H₇N)(C₁₆H₁₀N₂S)(CO)₃](CF₃SO₃), ( 2 ), and fac‐tricarbonyl[1,10‐phenanthroline‐κ²N ,N ′](4‐vinylpyridine‐κN )rhenium(I) trifluoromethanesulfonate, [Re(C₇H₇N)(C₁₂H₈N₂)(CO)₃](CF₃SO₃), ( 3 ). In all three complexes, the Re^I center resides in a distorted octahedral coordination environment. These complexes exhibit CO release upon exposure to low‐power UV light. The apparent CO release rates of the complexes have been measured to assess their comparative CO‐donating capacity. The three complexes are highly luminescent and this in turn provides a convenient way to track the entry of the prodrug molecules within biological targets.     

Synthesis,characterization and α‐amylase and α‐glucosidase inhibition studies of novel vanadyl chalcone complexes

A series of chalcone ligands and their corresponding vanadyl complexes of composition [VO (L^I–IV)₂(H₂O)₂]SO₄ (where L^I = 1,3‐Diphenylprop‐2‐en‐1‐one, L^II = 3‐(2‐Hydroxy‐phenyl)‐1‐phenyl‐propenone, L^III = 3‐(3‐Nitro‐phenyl)‐1‐phenyl‐propenone, L^IV = 3‐(4‐Methoxy‐phenyl)‐1‐phenyl‐propenone) have been synthesized and characterized using various spectroscopic (Fourier‐transform infrared, electrospray ionization mass, nuclear magnetic resonance, electron paramagnetic resonance, thermogravimetric analysis, vibrating sample magnetometer) and physico‐analytic techniques. Antidiabetic activities of synthesized complexes along with chalcones were evaluated by performing in vitro and in silico α‐amylase and α‐glucosidase inhibition studies. The obtained results displayed moderate to significant inhibition activity against both the enzymes by vanadyl chalcone complexes. The most potent complexes were further investigated for the enzyme kinetic studies and displayed the mixed inhibition for both the enzymes. Further, antioxidant activity of vanadyl chalcone complexes was evaluated for their efficiency to release oxidative stress using 2,2‐diphenyl‐1‐picryl‐hydrazyl‐hydrate assay, and two complexes (Complexes 2 and 4 ) have demonstrated remarkable antioxidant activity. All the complexes were found to possess promising antidiabetic and antioxidant potential.     

Synthesis,Characterization, and DNA‐Binding Properties of the Chiral Ruthenium(II) Complexes Δ‐ and Λ‐[Ru(bpy)2(dmppd)]2+ (dmppd = 10,12‐Dimethylpteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione; bpy = 2,2′‐Bipyridine)

Two novel chiral ruthenium(II) complexes, Δ‐[Ru(bpy)₂(dmppd)]²⁺ and Λ‐[Ru(bpy)₂(dmppd)]²⁺ (dmppd = 10,12‐dimethylpteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione, bpy = 2,2′‐bipyridine), were synthesized and characterized by elemental analysis, ¹H‐NMR and ES‐MS. The DNA‐binding behaviors of both complexes were studied by UV/VIS absorption titration, competitive binding experiments, viscosity measurements, thermal DNA denaturation, and circular‐dichroism spectra. The results indicate that both chiral complexes bind to calf‐thymus DNA in an intercalative mode, and the Δ enantiomer shows larger DNA affinity than the Λ enantiomer does. Theoretical‐calculation studies for the DNA‐binding behaviors of these complexes were carried out by the density‐functional‐theory method. The mechanism involved in the regulating and controlling of the DNA‐binding abilities of the complexes was further explored by the comparative studies of [Ru(bpy)₂(dmppd)]²⁺ and of its parent complex [Ru(bpy)₂(ppd)]²⁺ (ppd = pteridino[6,7‐f] [1,10]phenanthroline‐11,13 (10H,12H)‐dione).     

Ring‐opening polymerization of lactide, ε‐caprolactone and their copolymerization catalyzed by β‐diketiminate zinc complexes

A series of zinc silylamido complexes bearing non‐symmetric β ‐diketiminate ligands were synthesized and structurally characterized. Ring‐opening polymerization (ROP) of rac ‐lactide catalyzed by these zinc complexes afforded heterotactic polylactides at room temperature (P _r = 0.79 ~ 0.83 in THF). The steric and electronic characteristics of the ancillary ligands showed significant influence on the polymerization performance of the corresponding zinc complexes. All these zinc complexes also showed moderate activities toward the polymerization of ε ‐caprolactone at ambient temperature in toluene, producing polycaprolactones (PCLs) with high molecular weights and moderate polydispersities. PCL‐b ‐PLLA copolymers could be obtained via three different copolymerization strategies (one‐pot polymerization, and sequential addition of the two monomers in either order) by adopting complex 6 as the initiator through the adjustment of reaction temperatures. The diblock nature of the copolymers was confirmed by ¹³C NMR spectroscopy and DSC analysis.     

Synthesis and characterization of new complexes of the type [Ru(CO)2Cl2 (2‐phenyl‐1,8‐naphthyridine‐kN) (2‐phenyl‐1,8‐naphthyridine‐kN′)]. Preliminary applications in homogeneous catalysis

Novel ruthenium (II) complexes were prepared containing 2‐phenyl‐1,8‐naphthyridine derivatives. The coordination modes of these ligands were modified by addition of coordinating solvents such as water into the ethanolic reaction media. Under these conditions 1,8‐naphthyridine (napy) moieties act as monodentade ligands forming unusual [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] complexes. The reaction was reproducible when different 2‐phenyl‐1,8‐naphthyridine derivatives were used. On the other hand, when dry ethanol was used as the solvent we obtained complexes with napy moieties acting as a chelating ligand. The structures proposed for these complexes were supported by NMR spectra, and the presence of two ligands in the [Ru(CO)₂Cl₂(η¹‐2‐phenyl‐1,8‐naphthyridine‐ kN )(η¹‐2‐phenyl‐1,8‐naphthyridine‐kN′)] type complexes was confirmed using elemental analysis. All complexes were tested as catalysts in the hydroformylation of styrene showing moderate activity in N,N′‐dimethylformamide. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and structures of photoactive manganese–carbonyl complexes derived from 2‐(pyridin‐2‐yl)‐1,3‐benzothiazole and 2‐(quinolin‐2‐yl)‐1,3‐benzothiazole

PhotoCORMs (photo‐active CO‐releasing molecules) have emerged as a class of CO donors where the CO release process can be triggered upon illumination with light of appropriate wavelength. We have recently reported an Mn‐based photoCORM, namely [MnBr(pbt)(CO)₃] [pbt is 2‐(pyridin‐2‐yl)‐1,3‐benzothiazole], where the CO release event can be tracked within cellular milieu by virtue of the emergence of strong blue fluorescence. In pursuit of developing more such trackable photoCORMs, we report herein the syntheses and structural characterization of two Mn^I–carbonyl complexes, namely fac‐tricarbonylchlorido[2‐(pyridin‐2‐yl)‐1,3‐benzothiazole‐κ²N ,N ′]manganese(I), [MnCl(C₁₂H₈N₂S)(CO)₃], (1), and fac‐tricarbonylchlorido[2‐(quinolin‐2‐yl)‐1,3‐benzothiazole‐κ²N ,N ′]manganese(I), [MnCl(C₁₆H₁₀N₂S)(CO)₃], (2). In both complexes, the Mn^I center resides in a distorted octahedral coordination environment. Weak intermolecular C—H…Cl contacts in complex (1) and Cl…S contacts in complex (2) consolidate their extended structures. These complexes also exhibit CO release upon exposure to low‐power broadband visible light. The apparent CO release rates for the two complexes have been measured to compare their CO donating capacity. The fluorogenic 2‐(pyridin‐2‐yl)‐1,3‐benzothiazole and 2‐(quinolin‐2‐yl)‐1,3‐benzothiazole ligands provide a convenient way to track the CO release event through the `turn‐ON' fluorescence which results upon de‐ligation of the ligands from their respective metal centers following CO photorelease.     

Dual‐Sensitized Luminescent Europium(ΙΙΙ) and Terbium(ΙΙΙ) Complexes as Bioimaging and Light‐Responsive Therapeutic Agents

Dual‐photosensitized stable Eu^ΙΙΙ and Tb^ΙΙΙ complexes, namely [Eu(dpq)(tfnb)₃] ( 1 ) and [Tb(dpq)(tfnb)₃] ( 2 ), in which dpq=dipyrido[3,2‐d:2′,3′‐f]quinoxaline and Htfnb=4,4,4‐trifluoro‐1‐(2‐napthyl)‐1,3‐butanedione, were designed as bioimaging and light‐responsive therapeutic agents. Their X‐ray structures, photophysical properties, biological interactions, photoinduced DNA damage, photocytotoxicity, and cellular uptake properties were studied. Discrete mononuclear complexes adopt an eight‐coordinated {LnN₂O₆} distorted square antiprism geometry with bidentate N,N‐donor dpq and O,O‐donor tfnb ligands. The designed probes have the advantage of dual‐sensitizing antennae (dpq, Htfnb) to modulate their desirable optical properties for cellular imaging and light‐responsive intracellular damage. The remarkable photostability, absence of inner‐sphere water (q<1), and longer excited‐state lifetimes of the complexes make them suitable as cellular‐imaging probes. The dpq ³T state is well located energetically to allow efficient energy transfer (ET) to the emissive ⁵D₀ and ⁵D₄ states of Eu^ΙΙΙ and Tb^ΙΙΙ. This leads to higher quantum yields (φ=0.15–0.20) in aqueous media and makes these compounds suitable cellular‐imaging probes. The complexes display significant binding ability toward DNA and bovine serum albumin (K≈10⁵ m ^?1). They effectively cleave supercoiled DNA to its nicked circular form at λ=365 nm through photoredox pathways. The cellular internalization studies showed cytosolic and nuclear localization. The remarkable photocytotoxicity of these probes offers a strategy towards developing photoresponsive Ln^ΙΙΙ probes as cellular‐imaging and phototherapeutic agents.     

Synthesis,spectral and antibacterial activity of Co(II), Ni(II) and Zn(II) complexes with 2‐hydroxy‐benzoic acid(3,4‐dihydro‐2H‐naphthalen‐1‐ylidene)‐hydrazide

A bioactive Schiff base HL i.e. 2‐hydroxy‐benzoic acid(3,4‐dihydro‐2H ‐naphthalen‐1‐ylidene)‐hydrazide was synthesized by reacting equimolar amount of salicylic acid hydrazide and 1‐tetralone. Co(II), Ni(II) and Zn(II) complexes of ligand HL was synthesized in 1:1 and 1:2 molar ratio of metal to ligand. The structure of the synthesized ligand and metal complexes was established by elemental analysis, molar conductance, magnetic susceptibility measurements, electronic, IR and EPR spectral techniques. For determining the thermal stability the TGA has been done. In DFT studies the geometries of Schiff bases and metal complexes were fully optimized with respect to the energy using the 6–31 + g(d,p) basis set. Spectral data reveal that ligand behave uninegative tridentate in ML complexes and uninegative bidentate in ML₂ complexes. On the basis of characterization octahedral geometry has been assigned for Co(II) and Ni(II) complexes, while tetrahedral for Zn(II) complexes. Antibacterial activity of the synthesized compounds were evaluated against Staphylococcus aureus , Bacillus subtilis, Escherichia coli , Xanthomonas campestris and Pseudomonas aeruginosa and the results revealed that metal complexes show enhanced activity in comparison to free ligand.     

Bis(4,4′‐dimethyl‐2,2′‐bipyridine) ruthenium (II) Complexes Containing 2‐Arylimidazo‐ [4,5‐f] [1,10] phenanthroline: Syntheses,Characterization and Third‐order Nonlinear Optical Properties

Four novel mononuclear ruthenium(II) complexes [Ru(dmb)₂L]²⁺ [dmb = 4,4′‐dimethyl‐2,2′‐bipyridine, L = imidazo‐[4,5‐f][1,10]phenanthroline (IP), 2‐phenylimidazo‐[4,5‐f][1,10]phenanthroline (PIP), 2‐(4′‐hydroxyphenyl)imidazo‐[4,5‐f] [1,10] phenanthroline (HOP), 2‐(4′‐dimethylaminophenyl) imidazo‐[4, 5‐f] [1,10] phenanthroline (DMNP)] were synthesized and characterized by ES‐MS, ¹H NMR, UV‐vis and electrochemistry. The nonlinear optical properties of the ruthenium(II) complexes were investigated by Z‐scan techniques with 12 ns laser pulse at 540 nm, and all of them exhibit both nonlinear optical (NLO) absorption and self‐defocusing effect. The corresponding effective NLO susceptibility |x³| of the complexes is in the range of 2.68 × 10^?12‐4.57 × 10^?12 esu.     

Determination of Enantiomer Purity of β‐ and γ‐Amino Acids by NMR Analysis of Diastereoisomeric Palladium Complexes

Like α‐amino acids, β‐ and γ‐amino acids form spirobicyclic complexes (see 2 and 3 ) by reaction with the chiral di‐μ‐chlorobis{2‐[1‐dimethylamino‐ϰN)‐ethyl]phenyl‐ϰC}dipalladium complexes 1 under basic conditions (Scheme 1 and X‐ray structures in Fig. 1). The diastereoisomeric complexes formed with mixtures of enantiomers of either the amino acids or the dichloro‐dipalladium complexes give rise to marked chemical‐shift differences in the ¹H‐ and ¹³C‐NMR spectra (Figs. 2 – 4) to allow determination of the enantiomer purities. A simple procedure is described by which β‐ and γ‐amino acids (which may be generated in situ from Boc‐ or Fmoc‐protected precursors) are converted to the Pd complexes and subjected to NMR measurements. The effects of solvent, temperature, and variation of the aryl group in the chiral derivatizing Pd reagent are described (Figs. 4 and 5). The methyl esters of β‐amino acids can also be employed, forming diastereoisomeric chloro[(amino‐ϰN)aryl‐ϰC][(amino‐ϰN)alkanoate]palladium complexes 6 for determining enantiomer ratios (Scheme 6). The new method has great scope, as demonstrated for β²‐, β³‐, β^2,3‐, β^2,2,3‐, γ²‐, γ³‐, γ⁴‐, and γ^2,3,4‐amino acid derivatives.     

2‐(4′‐Pyridyl‐N‐oxide)‐Substituted Hemithioindigos as Photoresponsive Guests for a Super Aryl‐Extended Calix[4]pyrrole Receptor

We report the synthesis of two 2‐(4′‐pyridyl‐N‐oxide)‐substituted hemithioindigos (HTIs). We probed their photoisomerization by using UV/Vis and ¹H NMR spectroscopy techniques. Light irradiation at λ=450 nm provoked the isomerization of the HTI Z isomer to the E counterpart to a large extent (≈80 % at the photostationary state). ¹H NMR titration experiments revealed the formation of thermodynamically and kinetically stable 1:1 inclusion complexes of the (Z)‐HTI isomers with a super aryl‐extended host (association constant>10⁴ m ^?1). Photoirradiation at λ=450 nm of the inclusion complexes induced the isomerization of the bound HTI N‐oxide to afford the (E)‐HTI?calix[4]pyrrole complex. We determined accurate association constant values for the 1:1 inclusion complexes of the (Z)‐ and (E)‐HTI isomers by using isothermal titration calorimetry experiments. The results showed that the stability constants of the (E)‐HTI complexes were 2.2–2.8‐fold lower than those of the (Z)‐HTI counterparts, which explains the lack of light‐induced release of the former to the bulk solution.     

Novel half‐sandwich η5‐Cp *–rhodium(III) and η5‐Cp *–ruthenium(II) complexes bearing bis(phosphino)amine ligands and their use in the transfer hydrogenation of aromatic ketones

Two new half‐sandwich η⁵‐Cp*–rhodium(III) and η⁵‐Cp*–ruthenium(II) complexes have been prepared from corresponding bis(phosphino)amine ligands, thiophene‐2‐(N,N‐bis(diphenylphosphino)methylamine) or furfuryl‐2‐(N,N‐bis(diphenylphosphino)amine). Structures of the new complexes have been elucidated by multinuclear one‐ and two‐dimensional NMR spectroscopy, elemental analysis and IR spectroscopy. These Cp*–rhodium(III) and Cp*‐ruthenium(II) complexes bearing bis(phosphino)amine ligands were successfully applied to transfer hydrogenation of various ketones by 2‐propanol. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,Characterization, and DNA Interaction Studies of the Ruthenium(II) Complexes [Ru(bpy)2(ipbp)]2+ and [Ru(ipbp)(phen)2]2+ (ipbp=3‐(1H‐Imidazo[4,5‐f][1,10]phenanthrolin‐2‐yl)‐4H‐1‐benzopyran‐2‐one; bpy=2,2′‐Bipyridine; phen=1,10‐Phenanthroline)

A novel ligand 3‐(1H‐imidazo[4,5‐f][1,10]phenanthrolin‐2‐yl)‐4H‐1‐benzopyran‐4‐one (ipbp) and its ruthenium(II) complexes [Ru(bpy)₂(ipbp)]²⁺ ( 1 ) and [Ru(ipbp)(phen)₂]²⁺ ( 2 ) (bpy=2,2′‐bipyridine, phen=1,10‐phenanthroline) were synthesized and characterized by elemental analysis and mass, ¹H‐NMR, and electronic‐absorption spectroscopy. The electrochemical behavior of the complexes was studied by cyclic voltammetry. The DNA‐binding behavior of the complexes was investigated by spectroscopic methods and viscosity measurements. The results indicate that complexes 1 and 2 bind with calf‐thymus DNA in an intercalative mode. In addition, 1 and 2 promote cleavage of plasmid pBR 322 DNA from the supercoil form I to the open circular form II upon irradiation.     

1,2,4‐Triazol‐3‐ylidenes with an N‐2,4‐Dinitrophenyl Substituent as Strongly π‐Accepting N‐Heterocyclic Carbenes

The synthesis and characterisation of a series of new Rh and Au complexes bearing 1,2,4‐triazol‐3‐ylidenes with a N‐2,4‐dinitrophenyl (N‐DNP) substituent are described. IR, NMR, single‐crystal X‐ray diffraction and computational analyses of the Rh complexes revealed that the N‐heterocyclic carbenes (NHCs) behaved as strong π acceptors and weak σ donors. In particular, a natural bond orbital (NBO) analysis revealed that the contributions of the Rh→C_carbene π backbonding interaction energies (ΔE_bb) to the bond dissociation energies (BDE) of the Rh? C_carbene bond for [RhCl(NHC)(cod)] (cod=1,5‐cyclooctadiene) reached up to 63 %. The Au complex exhibited superior catalytic activity in the intermolecular hydroalkoxylation of cyclohexene with 2‐methoxyethanol. The NBO analysis suggested that the high catalytic activity of the Au^I complex resulted from the enhanced π acidity of the Au atom.     

Synthesis and electrical conductivity of some poly[4‐amino‐2,6‐pyrimidinodi‐thiocarbamate]–metal complexes

Poly[4‐amino‐2,6‐pyrimidinodithiocarbamate] was prepared from the reaction of 2‐mercapto‐4,6‐diaminopyrimidine with carbon disulfide, followed by condensation through the removal of H₂S gas. Five polymer–metal complexes of manganese, ferrous, ferric, zinc and mercury were then prepared. The polymer–metal complexes are investigated by elemental analyses, ultraviolet Fourier transform infrared and magnetic susceptibility. The DC electrical conductivity variation with the temperature in the region 298–498 K of the five polymer–metal complexes was determined. Doping with 5% ZnCl₂ increased the electrical conductivity of the polymer at all temperatures investigated. All the polymer–metal complexes showed an increase in conductivity with an increase in temperature, which is a typical semiconductor behavior. The proposed structure of the complexes is (MLX₂·mH₂O)_n. All the polymer–metal complexes are thermally stable, are insoluble in common organic solvents and have high melting points. Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesen und Strukturen von Bis(4,4′‐t‐butyl‐2,2′‐bipyridin)‐Ruthenium(II)‐Komplexen mit funktionellen Derivaten des Tetramethyl‐bibenzimidazols

Syntheses and Structures of Bis(4,4′‐t‐butyl‐2,2′‐bipyridine) Ruthenium(II) Complexes with functional Derivatives of Tetramethyl‐bibenzimidazole [(tbbpy)₂RuCl₂] reacts with dinitro‐tetramethylbibenzimidazole ( A ) in DMF to form the complex [(tbbpy)₂Ru( A )](PF₆)₂ ( 1a ) (tbbpy: bis(4,4′‐t‐butyl)‐2,2′bipyridine). Exchange of the two PF₆^? anions by a mixture of tetrafluor‐terephthalat/tetrafluor‐terephthalic acid results in the formation of 1b in which an extended hydrogen‐bonded network is formed. According to the ¹H NMR spectra and X‐ray analyses of both 1a and 1b , the two nitro groups of the bibenzimidazole ligand are situated at the periphery of the complex in cis position to each other. Reduction of the nitro groups in 1a with SnCl₂/HCl results in the corresponding diamino complex 2 which is a useful starting product for further functionalization reactions. Substitution of the two amino groups in 2 by bromide or iodide via Sandmeyer reaction results in the crystalline complexes [(tbbpy)₂Ru( C )](PF₆)₂ and [(tbbpy)₂Ru( D )](PF₆)₂ ( C : dibromo‐tetrabibenzimidazole, D : diiodo‐tetrabibenzimidazole). Furthermore, 2 readily reacts with 4‐t‐butyl‐salicylaldehyde or pyridine‐2‐carbaldehyde under formation of the corresponding Schiff base Ru^II complexes 5 and 6 . ¹H NMR spectra show that the substituents (NH₂, Br, I, azomethines) in 2 ‐ 6 are also situated in peripheral positions, cis to each other. The solid state structure of both 2 , and 3 , determined by X‐ray analyses confirm this structure. In addition, the X‐ray diffraction analyses of single crystals of the complexes [(tri‐t‐butyl‐terpy)(Cl)Ru( A )] ( 7 ) and [( A )PtCl₂] ( 8 ) display also that the nitro groups in these complexes are in a cis‐arrangement.     

Enantioselective Synthesis of β‐Blockers via Hydrolytic Kinetic Resolution of Terminal Oxiranes by Using Bimetallic Chiral {{2,2′‐[Cyclohexane‐1,2‐diylbis(nitrilomethylidyne)]bis[phenolato]}(2−)}cobalt ([Co(salen)])‐Type Complexes

The synthesis of chirally pure β‐blockers was successfully achieved via hydrolytic kinetic resolution of butyl (±)‐4‐(oxiran‐2‐ylmethoxy)benzeneacetate ((±)‐ 1 ) and (±)‐4‐(oxiran‐2‐ylmethoxy)benzeneacetonitrile ((±)‐ 2 ) in the presence of bimetallic chiral [Co(salen)]‐type complexes. The newly synthesized bimetallic chiral [Co(salen)]‐type complexes exhibited excellent enantioselectivities of up to >98% ee in good yields (Tables 1–3).