New N-heterocyclic carbene mercury(II) complexes: Close mercury-arene interaction

Mononuclear mercury complexes (1, 2, and 3) bearing bis-N-heterocyclic carbene (NHC) ligands of the form [(NHC)₂-μ-Hg]⁺² have been prepared and structurally characterised. The complexes were derived from three bis-imidazolium salts as precursors to NHC; either 1,3-bis(N-methylimidazolium-1-ylmethyl)benzene bis(hexafluorophosphate) (I·2PF₆), 1,3-bis(N-butylimidazolium-1-ylmethyl)benzene bis(hexafluorophosphate) (II·2PF₆) or 3,5-bis(N-butylimidazolium-1-ylmethyl)toluene bis(hexafluorophosphate) (III·2PF₆) treated with mercury(II) acetate. Interestingly X-ray crystal structure analysis revealed a close interaction between the Hg metal centre with one carbon atom of the aryl linker in addition to coordination with two NHCs.     

Spectral studies on mixed ligand complexes of sodium dinitro-bis(acetylacetonato) cobaltate(iii) with imida-zole ligands

A number of mixed ligand complexes, nitro(imidazole) bis(acetylacetonato) cobaltate(III), [Co(acac)₂ (NO₂ )₂ (L)] (L = imidazole or substituted imidazole) have been synthesised and characterised on the basis of chemical analyses, IR, electronic, mass and nuclear (¹H and ¹³C) magnetic resonance spectra as well as TGA and DTA data. All complexes are non-electrolytic and possess a trans octahedral structure. The NO₂^? group is coordinated through the N atom. Though the ¹H NMR data of fresh CDCl₃ solutions of complexes confirm the trans structure, slow isomerisation to the cis configuration is observed at room temperature.     

Luminescent cyclometallated platinum(II) complexes with N-benzoyl thiourea derivatives as ancillary ligands

A series of cyclometallated 2-phenylpyridine Pt(II) complexes having N-benzoyl thiourea derivatives as ancillary ligands were prepared and characterised by elemental analysis, IR and UV–Vis spectroscopy, ¹H and ¹³C NMR spectroscopy as well as by X-ray diffraction on single-crystal. All complexes were obtained as a single isomer with N atom of the 2-phenylpyridine ligand and S atom of the N-benzoyl thiourea derivatives coordinated in trans positions to the platinum metal as evidenced by using X-ray crystallography and NMR spectroscopy. All Pt(II) complexes show good luminescence properties at room temperature, both in dichloromethane solution and in solid state.     

Bridge cleavage reactions of cyclopalladated nitrosamines with thioamides and related compounds

The palladacycle [Pd(μ-O₂CMe){κ²C,N-4-MeC₆H₃N(Me)NO}]₂ readily undergoes bridge cleavage reactions with a variety of compounds containing donor functionalities including thioamides, 8-hydroxyquinoline, thioureas, selenoureas, acetylacetone derivatives, dithiocarbamates, xanthates, as well as bidentate N-donors to afford either the monomeric, neutral Pd(II) complexes [Pd{κ²C,N-4-MeC₆H₃N(Me)NO}{L-L}] or the monocationic complexes [Pd{κ²C,N-4-MeC₆H₃N(Me)NO}(N-N)]PF₆ in high yields. A series of 15 different complexes was prepared and fully characterised spectroscopically and, in some cases, by X-ray diffraction. It was also found that the dithiocarbamato complex undergoes a disproportionation reaction in solution to give the bis(cyclometallated) complex [Pd{κ²C,N-4-MeC₆H₃N(Me)NO}₂] as well as the bis(dithiocarbamato) complex [Pd{κ²S-S₂CNEt₂}₂].     

Reductive carbonylation of nitrobenzene to phenylurethane catalyzed by Ru(III)-schiff base complexes

Ruthenium complexes containing Schiff bases with N₂O₂, N₄ and N₅ donor groups with the general formula [Ru^III(X)Cl_{1 or 2}], where X = Schiff base such as bis(salicylaldehyde)-o-phenylenediimine (saloph), bis(salicylaldehyde)ethylenediimine (salen), bis(picolaldehyde)ethylenediimine (picen), bis(picolaldehyde)-o-phenylenediimine (pic-opd), bis(picolaldehyde)diethylenetriimine (pic-dien), were tested for their catalytic activity towards the reductive carbonylation of nitrobenzene in ethanol to give phenylurethane. The five Ru(III) complexes tested towards reductive carbonylation showed different catalytic activities in the range 160 – 200 °C and CO partial pressure of 15 atm.Among the complexes tested, [Ru(saloph)Cl₂] showed the highest catalytic activity with a turnover rate greater than 80 mol product per mol catalyst per hour at 160 °C and 15 atm CO. [Ru(pic-en)Cl₂]Cl and [Ru(picopd)Cl₂]Cl complexes with N₄ donor systems were found to be less active towards carbonylation of nitrobenzene, as indicated by their turnover rates of 20 and 15 mol product per mol catalyst per hour, respectively, at 200 °C and 15 atm CO. The complex [Ru(pic-dien)Cl]Cl₂N₅ donor system was completely inactive even at 200 °C and 15 atm CO, and no conversion of nitrobenzene was seen even after 12 h contact time.     

Silver(I) and mercury(II) complexes of meta- and para-xylyl linked bis(imidazol-2-ylidenes)

Mononuclear silver and mercury complexes bearing bis-N-heterocyclic carbene (NHC) ligands with linear coordination modes have been prepared and structurally characterised. The complexes form metallocyclic structures that display rigid solution behaviour. A larger metallocycle of the form [L₂Ag₂]²⁺ [where L = para-bis(N-methylimidazolylidene)xylylene] has been isolated from the reaction of para-xylylene-bis(N-methylimidazolium) chloride and Ag₂O. Reaction of silver- and mercury-NHC complexes with Pd(NCCH₃)₂Cl₂ affords palladium-NHC complexes via NHC-transfer reactions, the mercury case being only the second example of a NHC-transfer reaction using a mercury-NHC complex.     

Iridium(III) Complexes with Sulfonyl and Fluorine Substituents: Synthesis,Stereochemistry and Effect of Functionalisation on their Photophysical Properties

The synthesis and photophysical and electrochemical characterisation of new heteroleptic iridium complexes with electron‐withdrawing sulfonyl groups and fluorine atoms bound to phenylpyridine ligands are reported. The emission energy of these materials strongly depends on the position of the sulfonyl groups and on the number of fluorine substituents. A 90 nm wide tuning range of photoluminescence from the blue‐green (λ_em=468 nm) of iridium(III)bis[2‐(4′‐benzylsulfonyl)phenylpyridinato‐N,C2′][3‐(pentafluorophenyl)‐pyridin‐2‐yl‐1,2,4‐triazolate] to the orange (λ_em=558 nm) of iridium(III)bis[2‐(3′‐benzylsulfonyl)phenylpyridinato‐N,C2′](2,4‐decanedionate) has been achieved. Emission quantum yields ranging from 47 to 71 % have also been found for degassed solutions of the complexes, and a surprisingly high value of 16 % was recorded for iridium(III)bis[2‐(5′‐benzylsulfonyl‐3′,6′‐difluoro)phenylpyridinato‐N,C2′](2,4‐decanedionate) in air‐equilibrated dichloromethane. A unusual stereochemistry of the benzylsulfonyl‐substituted dimer and heteroleptic complexes has been detected by ¹H NMR spectroscopy, and is characterised by the mutual cis disposition of the pyridyl nitrogen atoms of the phenylpyridine ligands, which differs from the most common trans arrangement reported in the literature.     

Palladium, rhodium and platinum complexes of ortho-xylyl-linked bis-N-heterocyclic carbenes: Synthesis, structure and catalytic activity

New Pd(II), Pt(II) and Rh(I) N-heterocyclic carbene (NHC) complexes containing two NHC units linked by an ortho-xylyl group are described and structurally and spectroscopically characterised. The Pt(II) complexes represent the first examples of Pt-bis(NHC) complexes where the NHC units are linked by an ortho-xylyl group. Functionalisation of the bis(NHC) ligands with heptyl groups has been used as a means of enhancing the solubility of the complexes, in order to facilitate spectroscopic characterisation and catalytic studies. The catalytic activity of the palladium(II) complexes in Heck and Suzuki cross-coupling reactions has been examined to investigate any effects of the diverse structural changes, though these appear to be insignificant.     

Zur reaktivität komplexgebundener carbocyclen: XV. Neue wege zu indenyl-diolefen-komplexen von cobalt und rhodium

The formation of (indenyl)rhodium(diolefin) complexes is described, using bis(indenyl) magnesium. On protonation of these complexes an η⁵-η⁶ shift of the indenyl ligand is observed. The corresponding cobalt complexes are obtained by lithium reduction of bis(indenyl)cobalt in the presence of the diolefin. The bidentate ligand 1,5-cyclooctadiene is readily replaced in these complexes by carbon monoxide. All compounds were characterised by ¹³C NMR spectroscopy.     

The synthesis and characterization of melamine based Schiff bases and its trinuclear [salen/salophenFe(III)] and [salen/salophenCr(III)] capped complexes

Four new trinuclear Fe(III) and Cr(III) complexes involving tetradentate Schiff bases N, N′-bis(salicylidene)ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophen H₂) with 2,4,6-tris(4-carboxybenzimino)-1,3,5-triazine have been synthesized and characterized by means of elemental analysis, ¹H NMR, FT-IR spectroscopy, LC-MS, thermal analyses and magnetic susceptibility measurements. The complexes have also been characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by COO^? group.     

Photophysical and electrochemical properties of heteroleptic tris-cyclometallated Ir(III) complexes

Some new heteroleptic tris-cyclometallated iridium(III) complexes have been synthesized and fully characterized. Among these iridium(III) complexes, bis(1-phenylpyrazolato-N,C^2′)iridium(III)[5-(2′-pyridyl)tetrazolate] (3) and bis(3-methyl-1-phenylpyrazolato-N,C^2′)iridium(III)[5-(2′-pyridyl)tetrazolate] (4) show excellent quantum yields at room temperature, the electron density being perturbed by introducing the pyridyltetrazole ligand, making k_r > k_nr. This destroys the concept of phenylpyrazole based iridium complexes.     

Synthesis,molecular structure and biological activity of Niii complexes based on substituted 2-(2-hydroxyphenyl)benzoxazole

New Niⁱⁱ complexes based on the substituted 2-(2-hydroxy-phenyl)benzoxazole have been synthesized from the corresponding ligands and nickel acetate. The crystal structure of bis[2-(1,3-benzoxazol-2-yl-κN)-4,5-dichloro-3-(methoxycarbonyl)phenolate-κO]nickel(ii) has been determined by X-ray diffraction. The new Niⁱⁱ complexes have been screened for their antibacterial, protistocidal and fungistatic activities     

The synthesis and characterization of 2,4,6-tris(3,4-dihydroxybenzimino)-1,3,5-triazine and its [salen/salophenFe(III)] and [salen/salophenCr(III)] capped complexes

Four new trinuclear Fe(III) and Cr(III) complexes involving tetradentate Schiff bases N,N′-bis(salicylidene)ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophenH₂) with 2,4,6-tris(3,4-dihydroxybenzimino)-1,3,5-triazine have been synthesized and characterized by means of elemental analysis, ¹H N.M.R., FT-IR spectroscopy, thermal analyses and magnetic susceptibility measurements. The complexes have also been characterized as low-spin distorted octahedral Fe(III) and Cr(III) bridged by catechol group.     

Structure-biodistribution relation of neutral Tc(CO)3-complexes with tridentate N-substituted derivatives of aminoethylglycine and phenylenediamine

Derivatives of ethylenediamine-N-acetic acid (EDAA = N-aminoethylglycine = AEG) and ortho-phenylenediamine-N-acetic acid (PDAA) with uncharged substituents on one or both of the amines form neutral complexes with a [^99mTc(CO)₃]⁺-moiety. We studied the influence of different modifications at the amines (e.g., with methyl, ethyl, butyl or benzyl groups) on the behaviour of the ^99mTc(CO)₃-complexes in vivo in mice, with special focus on blood-brain barrier (BBB) passage. The complexes have been characterised by reversed phase HPLC, log P, electrophoresis and some of them also by LC-MS. Log P values of the ^99mTc-tricarbonyl complexes varied from −0.52 (AEG) to 2.5 (N,N′-dibenzyl-EDAA). With increasing lipophilicity, more of the activity was found in liver and intestines as compared to kidneys and urine for the more polar complexes. Brain uptake was found for the ^99mTc(CO)₃-complexes with N,N′-dibutyl-ethylenediamine-N-acetic acid (0.34% of I.D. after 2 min) and ortho-phenylenediamine-N-acetic acid (0.22% of I.D. after 2 min).     

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.     

{Bis[N,N′-(2-alkyl-6-para-methylphenyl)phenyl)imino]acenaphthene}dibromonickel catalysts bearing bulky methylphenyl groups: synthesis,characterization, crystal structures and application in catalytic polymerization of ethylene and styrene

Two new Ni(II) complexes containing methylphenyl groups, {bis[N,N′-(2,6-dimethyl-4-p-methylphenylphenyl)imino]acenaphthene}dibromonickel 4a and {bis[N,N′-(2-ethyl-4,6-di(p-methylphenyl)phenyl)imino]acenaphthene}dibromonickel 4b, were synthesized and characterized. The molecular structures of both complexes were determined by single-crystal X-ray diffraction. Both complexes have pseudo-tetrahedral geometry about the nickel center, showing pseudo C _2v and C ₂ molecular symmetry, respectively. Complex 4c, {bis[N,N′-(2,4,6-trimethylphenyl)imino]acenaphthene}dibromonickel, was also synthesized for comparison. These complexes were tested as catalysts for the polymerization of ethylene and styrene under mild conditions using diethylaluminum chloride. The precatalyst 4b bearing one ortho-ethyl group and two bulky p-methylphenyl groups in the ortho- and para-aryl position of the ligand, displayed highly catalytic activity for the polymerization of ethylene [4.70 × 10⁶ g PE/(mol Ni h bar)], and produced branched polyethylene (76 methyl, 8 ethyl, 5 propyl and 22 butyl or longer branches/1,000 C at 60 °C). Interestingly, complex 4b also displays high catalytic activity [5.46 × 10⁵ g polystyrene/(mol Ni·h)] for styrene polymerization and produces nearly atactic polystyrene at 70 °C (stereo-triad distributions: rr, 39.9 %; mr, 30.4 %; mm, 29.8 %; stereo-diad distributions: r, 55.1 %; m, 44.9 %).     

Luminescent Dinuclear Bis‐Cyclometalated Gold(III) Alkynyls and Their Solvent‐Dependent Morphologies through Supramolecular Self‐Assembly

A series of luminescent bis‐cyclometalated gold(III) complexes containing bridging alkynyl ligands of different natures has been synthesised and characterised. The photophysical properties of the complexes have been investigated through electronic absorption spectroscopy and emission studies. The vibronic emission bands are found to originate from the triplet intraligand (IL) π–π* excited states of the bis‐cyclometalating ligands with some mixing of ³IL π–π* character of the alkynyl ligands. The electrochemical study of a nonsymmetric dinuclear complex shows two successive reduction processes originating from the reductions of the two different cyclometalating ligands. The complexes are found to undergo supramolecular self‐assembly processes driven by π–π stacking and hydrophobic/hydrophilic interactions to give honeycomb nanostructures, as revealed from the SEM images. Solvent‐dependent morphological transformations have also been observed, which have been studied by SEM and ¹H NMR spectroscopy.     

Rotamers of palladium complexes bearing IR active N-heterocyclic carbene ligands: Synthesis, structural characterization and catalytic activities

The preparation and properties of mono- versus bis(carbene) Pd(II) complexes bearing unsymmetrical cyano- and ester-functionalized NHC ligands as potential IR probes were studied in detail. Direct reaction of Pd(OAc)₂ with functionalized imidazolium salts afforded either bis(carbene) (3a, c) or monocarbene complexes (5, 6) with a N-coordinated imidazole co-ligand. The latter were exclusively obtained with N-ethylene substituted salts, which were found to undergo N-C cleavage reaction. The milder Ag-carbene transfer reaction on the other hand was tolerable to the length of the substituents and the nature of the functional groups. All bis(carbene) complexes (3a-c, 4a-c) were obtained as a inseparable mixture of square-planar trans-anti and trans-syn rotamers. The identity, ratio and dynamic equilibrium of these rotamers have been investigated and the relatively high rotational barrier for rotamers of 3a was estimated to be about 74 kJ mol⁻¹ at 380 K. All eight complexes were fully characterized by NMR and IR spectroscopies, ESI mass spectrometry and X-ray single crystal and powder diffraction. A preliminary catalytic study showed that ester-functionalized complexes 4a and 4b gave rise to highly active catalyst in the double Mizoroki-Heck coupling of aryl dibromides, while the in situ ester-hydrolyzed complexes were also active in the coupling of activated aryl chlorides.     

Coordination compounds of copper and nickel with N,N′-[4,4′-(perfluoro-1,4-phenylene)bis(oxy)bis(4,1-phenylene)]-bis[2-(pyridin-2-ylmethylidene)hydrazinecarbothioamide] and its derivatives

N,N′-[4,4′-(Perfluoro-1,4-phenylene)bis(oxy)bis(4,1-phenylene)]bis[2-(pyridin-2-ylmethylidene)-hydrazinecarbothioamide] as well as its methyl and phenyl derivatives react with copper and nickel chlorides in ethanol to form coordination compounds. In the products, the hydrazinecarbothioamides act as doubly deprotonated bridging ligands. The prepared complexes have been found to inhibit in vitro the growth and propagation of the myeloid human leukemia HL-60 cancer cells at the 10^?5–10^?7 mol/L concentration.     

Copper(II) complexes containing chiral substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine ligands: Synthesis, X-ray structural studies and asymmetric catalysis

New chiral N,N-bidentate ligands derived from substituted 2-(4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridines have been prepared and characterised by means of ¹H, ¹³C NMR spectroscopy and optical rotation. Their Cu(II) complexes were characterized by means of elemental analysis, ¹H NMR spectroscopy and MS. By means of X-ray diffraction, molecular geometry of the complex of 2-(1-methyl-4-isopropyl-4-methyl-4,5-dihydro-1H-imidazol-5-one-2-yl)pyridine with copper(II) chloride was determined. The complex exhibits heterochiral dimeric arrangement of two square pyramids with one terminal and one bridge-forming chlorine atoms and two nitrogen atoms in the bases of the pyramids. The tops of these pyramids are formed by the remaining chlorine atoms. The complexes prepared catalyse the Henry reaction with the overall yields of 41-97% and with the maximum enantioselective excess of 19%.