Structure-dependent spectroscopic and redox properties of copper(I) complexes with bidentate iminopyridine ligands

A series of iminopyridine ligands; cyclopropylpyridin-2-ylmethyleneamine (A), cyclopentylpyridin-2-ylmethyleneamine (B), cyclohexylpyridin-2-ylmethyleneamine (C), and cycloheptylpyridin-2-ylmethyleneamine, (D) and their copper(I) complexes, [Cu(L)₂]⁺ (1a-1d) and [Cu(L)(PPh₃)₂]⁺ (2a-2d) have been synthesized and characterized by CHN analyses, ¹H NMR and IR and UV-Vis spectroscopy. Structures of 1a, 1b, 1c and 2a were determined by X-ray crystallography. The coordination polyhedron about the Cu^I center in the complexes is best described as a distorted tetrahedron. The dihedral angles between the least-squares planes of the chelate ligands show considerable variation from 86.1° in 1a to 68.3° in 1b, indicating the importance of packing forces in the crystalline environment. The UV-Vis spectra of the complexes are characterized by first metal to ligand charge transfer bands increasing in wavelength with increasing size of the ring substituents in the ligands, except for the cyclopropyl compounds (1a and 2a), in good agreement with the variation of the dihedral angles between the ligand planes. Cyclic voltammetry of the complexes indicates a quasireversible redox behavior for the complexes. The bulkier ligands (PPh₃) inhibit the geometric distortion within the oxidized form and the redox potentials of complexes 2a-2d are shifted to more positive values, therefore.     

Diheteroarylmethyl substituted titanocenes: A novel class of possible anti-cancer drugs

From the reaction of tert-butyl lithium or n-butyl lithium with N-methylpyrrole (1a), furan (1b) or 2-bromo-thiophen (1c), 2-N-methylpyrrolyl lithium (2a), 2-furyl lithium (2b) or 2-thiophenyl lithium (2c), respectively, was obtained. When reacted with 6-(2-N-methylpyrrolyl) fulvene (3a), 6-(2-furyl) fulvene (3b) or 6-(2-thiophenyl) fulvene (3c), the corresponding lithiated intermediates were formed (4a-c). Titanocenes (5a-c) were obtained through transmetallation with titanium tetrachloride. When these titanocenes were tested against pig kidney epithelial (LLC-PK) cells, inhibitory concentrations (IC₅₀) of 32 μM, 140 μM, and 240 μM, respectively, were observed. These values represent improved cytotoxicity against LLC-PK, compared to their ansa-analogues.     

Thermal solvent-free synthesis of novel pyrazolyl chalcones and pyrazolines as potential antimicrobial agents

A novel approach was adopted for the synthesis of series of new pyrazolyl chalcones (3a-c) by the reaction of 5-chloro-3-methyl-1-phenylpyrazole-4-carboxaldehyde (1) with different 5-acetylbarbituric acid derivatives (2a-c) under thermal solvent-free condition. The chalcones were then converted to the corresponding pyrazolines (4a-c) under the same condition in excellent yields. All the synthesized compounds were characterized using elemental analysis and spectral data (IR, ¹H NMR, and mass spectrometry). The synthesized compounds were tested for their antimicrobial activity by disk diffusion assay with slight modifications against Gram-positive, Gram-negative strains of bacteria as well as fungal strains. The investigation of antimicrobial screening revealed that compounds (3a-4c) showed good antibacterial and antifungal activities, respectively. Among the screened compounds, 3b showed more potent inhibitory activity (MIC = 12.5 μg/ml) nearly to that of standard antibiotics ciprofloxacin, griseofulvin and fluconazole.     

Exploration of antimicrobial and antioxidant potential of newly synthesized 2,3-disubstituted quinazoline-4(3H)-ones

A series of 2-(chloromethyl)-3-(4-methyl-6-oxo-5-[(E)-phenyldiazenyl]-2-thioxo-5,6-dihydropyrimidine-1(2H)-yl)quinazoline-4(3H)-ones 9a-j was synthesized by treating 2-(chloroacetyl)amino benzoic acid with 3-amino-6-methyl-5-[(E)-phenyldiazenyl]-2-thioxo-2,5-dihydropyrimidine-4(3H)-one 8a-j and was screened for in vitro antibacterial activities against a representative panel of Gram-positive and Gram-negative bacteria. The compounds were synthesized in excellent yields and the structures were corroborated on the basis of IR, ¹H NMR, Mass and elemental analysis data. All the synthesized compounds elicited the potent inhibitory action against all the tested bacterial stains. Furthermore, in order to explore the antioxidant potential of newly synthesized compounds, the free radical scavenging activity measurement were performed by the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) assay method. It is revealed from the antioxidant screening results that the compounds 9c and f manifested profound antioxidant potential.     

Synthesis and complexation of tetrakis(diphenylphosphinomethyl)calix[4]arene adopting the 1,3-alternate conformation

Novel upper-rim modified tetraphosphinocalix[4]arenes (5a-b) adopting 1,3-alternate conformation have been synthesized. Reaction of 5,11,17,23-tetrachloromethyl-25,26,27,28-tetrahydroxycalix[4]arene (1) with Ph₂POEt gave 5,11,17,23-tetrakis(diphenylphosphinoylmethyl)-25,26,27,28-tetrahydroxycalix[4]arene (2). Tetra-O-substitution of 2 with n-propyl iodide or benzyl bromide in the presence of K₂CO₃ carried out to afford 5,11,17,23-tetrakis(diphenylphosphinoylmethyl)-25,26,27,28-tetrapropoxy-(3a) or -benzyloxycalix[4]arene (3b), whereas di-O-substituted calix[4]arene, 5,11,17,23-tetrakis(diphenylphosphinoylmethyl)-25,27-dipropoxy-26,28-dihydroxycalix[4]arene (4), was obtained exclusively when Na₂CO₃ was used as base. Reduction of 3a-b with PhSiHCl₂ afforded 5,11,17,23-tetrakis(diphosphinomethyl)-25,26,27,28-tetrapropoxy-(5a) and -tetrabenzyloxycalix[4]arene (5b). ¹H and ¹³C NMR analysis reveals that the phosphines (5a-b) and the tetra-O-substituted phosphine oxides (3a-b) adopt 1,3-alternate conformation, while the parent tetrahydroxy-(2) and the di-O-propylated phosphine oxide (4) adopt cone-conformation. The X-ray structure indicates that the calix[4]arene moieties in 4 a pinched-cone conformation in solid state. Complexation of the phosphine ligand (5a) with [RuCl₂(p-cymene)]₂ affords the tetranuclear complexes, [{RuCl₂(p-cymene)}₂ · 5a] (6), as 1,3-alternate conformer.     

Lewis acidity of platinum(II)-based Baeyer-Villiger catalysts: An electrochemical approach

The electrochemical behavior of the Pt(II)-based Baeyer-Villiger catalysts of the general formulae [Pt(μ-OH)(P^∩P)]₂(BF₄)₂ (P^∩P = dppe (1a), 2Fdppe (1 b), 4Fdppe (1c), dfppe (1d), dmpe (1e), depe (1f), dippe (1g), dtbpe (1h)) and [Pt(OH₂)₂(P^∩P)](OTf)₂ (P^∩P = dppe (2a), 2Fdppe (2b), 4Fdppe (2c), dfppe (2d)) is reported. They exhibit irreversible reduction processes whose potentials reflect the Lewis acidity of the metal centres, showing (for the aromatic diphosphine complexes) overall relations with the number of fluorine atoms, with J_Pt-P, with the ν(CN) coordination shift of a ligand isocyanide probe and with the catalytic activity. Single-crystal X-ray diffraction analyses were carried out for [Pt(μ-OH)(4Fdppe)]₂(BF₄)₂ (1c) and [Pt(μ-OH) (dippe)]₂(BF₄)₂ (1g).     

Synthesis and evaluation of chromenyl barbiturates and thiobarbiturates as potential antitubercular agents

A novel series of barbiturate and thiobarbiturate analogs of 2-benzoyl-3-methyl-5-oxo-5H-furo[3,2-g]chromene-6-carbaldehydes (3a-g and 4a-d, respectively) and 6-methyl-4,8-dioxo-4,8-dihydropyrano[3,2-g]chromenes (7a-c), were synthesized and evaluated for their antitubercular activities against Mycobacterium tuberculosis H37RV, and cytotoxicity (CC₅₀) in the VERO cell MABA assay. The results indicate that the furanochromene series of compounds (3a-g and 4a-d) showed only weak to moderate antitubercular activity. However, the pyranochromene analog 7b showed good antitubercular activity (IC₉₀: 5.9 μg/mL) and cytotoxicity (CC₅₀: 14.27 μg/mL). The antitubercular activity of 7b was superior to the antituberculosis drug, pyrazinamide (PZA; IC₉₀: >20 μg/mL). Analog 7b was considered to be a lead compound for subsequent structural optimization.     

Synthesis, X-ray structures, electrochemical properties and cytotoxic effects of Co(II) complexes

1-Benzothiazol-2-yl-3,5-dimethyl-1H-pyrazole (1a) and 1-benzothiazol-2-yl-5-(2-hydroxyphenyl)-3-methyl-1H-pyrazole-4-carboxylic acid methyl ester (1b) were reacted with the hexahydrates of cobalt(II) chloride, cobalt(II) nitrate and cobalt(II) perchlorate to give the corresponding complexes 2a-4a and 2b-5b, respectively. Obtained compounds differ in coordination spheres of central atoms. The complex 2a includes a fivefold coordinated cobalt(II) ion, whereas 3a shows a distorted octahedral configuration around the cobalt(II) ion. All complexes were characterised by FTIR spectroscopy, MS and elemental analysis. The X-ray structures of 2a, 3a and 5b complexes were also solved. The cytotoxic properties of the ligand 1a and both series of Co(II) complexes were examined on human leukemia NALM-6 and HL-60 cells and melanoma WM-115 cells. The ligands, were found to have very low cytotoxicity. Complex 3b exhibited the highest cytotoxic activity with IC₅₀ values in the range of 6.9-17.1 μM for three examined cell lines.     

Synthesis of 4,6-dideoxy-3-fluoro-2-keto-β-d-glucopyranosyl analogues of 5-fluorouracil, N-benzoyl adenine, uracil, thymine, N-benzoyl cytosine and evaluation of their antitumor activities

The synthesis of the unsaturated 4,6-dideoxy-3-fluoro-2-keto-β-d-glucopyranosyl nucleosides of 5-fluorouracil (6a), N⁶-benzoyl adenine (6b), uracil (6c), thymine (6d) and N⁴-benzoyl cytosine (6e), is described. Monoiodination of compounds 1a,b, followed by acetylation, catalytic hydrogenation and finally regioselective 2′-O-deacylation afforded the partially acetylated dideoxynucleoside analogues of 5-fluorouracil (5a) and N⁶-benzoyl adenine (5b), respectively. Direct oxidation of the free hydroxyl group at the 2′-position of 5a,b, with simultaneous elimination reaction of the β-acetoxyl group, afforded the desired unsaturated 4,6-dideoxy-3-fluoro-2-keto-β-d-glucopyranosyl derivatives 6a,b. Compounds 1c-e were used as starting materials for the synthesis of the dideoxy unsaturated carbonyl nucleosides of uracil (6c), thymine (6d) and N⁴-benzoyl cytosine (6e). Similarly a protection-selective deprotection sequence followed by oxidation of the free hydroxyl group at the 2′-position of the dideoxy benzoylated analogues 9c-e with simultaneous elimination reaction of the β-benzoyl group, gave the desired nucleosides 6c-e. None of the compounds was inhibitory to a broad spectrum of DNA and RNA viruses at subtoxic concentrations. The 5-fluorouracil derivative 6a was more cytostatic (50% inhibitory concentration ranging between 0.2 and 12 μM) than the other compounds.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Synthesis and structural characterization of mercury(II) complexes with a novel ferrocenyliminophosphine

Synthesis of the novel ligand ferrocenyliminophosphine [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)CHN(C₆H₄-2-PPh₂)}] (1, L) and studies on its complexation properties with mercury (II) are reported. Halogen-bridged binuclear mercury (II) complexes [HgX(μ-X)L]₂ (X = Cl (2a), Br (2b)) and a mononuclear mercury (II) complex HgCl₂L₂ (4a) have been obtained under different reaction conditions. In both cases, the ferrocenyliminophosphine acts as a P-monodentate ligand and the imino nitrogen does not participate in coordination to mercury (II). All the new compounds 1, 2a, 2b and 4a were characterized by elemental analysis, ¹H NMR, ³¹P NMR and IR spectra. In addition, structures of 2a and 4a have been determined by X-ray single-crystal analysis.     

Synthesis and biological evaluation of glycal-derived novel tetrahydrofuran 1,2,3-triazoles by ‘click’ chemistry

Thirteen new 1,2,3-triazoles (5a-e, 15a-d, 17a-b, 19, and 21) were synthesized by ‘click’ reaction of sugar-derived azides with commercially available acetylenes. The synthesized triazoles were tested in vitro for their biological activity, and compound 5b displayed both antibacterial and antifungal activities at an MIC value of 12.5 μg/mL, while compounds 15b and 19 showed antibacterial activity at an MIC value of 25 μg/mL.     

Dopamine release and molecular modeling study of some coumarin derivatives

4-aryl-2-amino-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)-pyridin-3-carbonitrile (1), 4-aryl-2-oxo-6-(4-hydroxy-2-oxo-2H-chromen-3-yl)-pyridin-3-carbonitriles (2a-2c), 3-(6-aryl-1,2,5,6- tetrahydro-2-thioxopyrimidin-4-yl)-4-hydroxy-2H-chromen-2-one (3a, 3b) and pyrazol-3-yl-4-hydroxycoumarin derivatives (4a-4c, 5, 6a, 6b, 7a, 7b, and 8a-8c) were prepared in order to measure their % change dopamine release in comparison to amphetamine as reference, using PC-12 cells in different concentrations. In addition, the molecular modeling study of the compounds into 3BHH receptor was also demonstrated. The calculated inhibition constant (k_i) implemented in the AutoDock program revealed identical correlation with the experimental results to that obtained binding free energy (ΔG_b) as both parameters revealed reasonable correlation coefficients (R²) being 0.51 involving 10 compounds; (1, 2b, 2c, 3a, 3b, 4a, 4b, 6a, and 8c).     

Synthesis, characterization, crystal structures and photophysical properties of copper(I) complexes containing 1,1′-bis(diphenylphosphino)ferrocene (B-dppf) in doubly-bridged mode

Five copper(I) complexes having general formula [Cu₂(μ-X)₂(κ²-P,P-B-dppf)₂] (X = Cl(1), Br(2), I(3), CN(4), and SCN(5)) were prepared starting with CuX and B-dppf in 1:1 molar ratio in DCM-MeOH (50:50 V/V) at room temperature. The complexes have been characterized by elemental analyses, IR, ¹H NMR, ³¹P NMR and electronic spectral studies. Molecular structures for 1, 2 and 4 were determined crystallographically. Complexes 1, 2 and 4 exist as centrosymmetric dimers in which the two copper atoms are bonded to two bridging B-dppf ligands and two bridging (pseudo-)halide groups in a μ-η¹ bonding mode to generate nearly planar Cu₂(μ-η¹-X)₂ framework. Both bridging B-dppf ligands are arranged in antiperiplanar staggered conformation in 1 and 2 (mean value 56.40-56.76°), and twisted from the eclipsed conformation (mean value 78.19°) in 4. The Φ angle value in 4 is relatively larger as compared to 1 and 2. This seems to indicate that the molecular core [Cu₂(μ-η¹-X)₂] in 4 is a sterically demanding system that forces the B-dppf ligand to adopt a relatively strained conformation in comparison to less strained system in 1 and 2. All the complexes exhibit moderately strong luminescence properties in the solution state at ambient temperature.     

Influence of the phosphine arrangement on the reactivity of palladium(II) and platinum(II) polyphosphine complexes with copper(I) chloride

The distorted square-planar complexes [Pd(PNHP)Cl]Cl (1) (PNHP = bis[2-(diphenylphosphino)ethyl]amine), [M(P₃)Cl]Cl [P₃ = bis[2-(diphenylphosphino)ethyl]phenylphosphine; M = Pd (2), Pt (3)] and [Pt(NP₃)Cl]Cl (5) (NP₃ = tris[2-(diphenylphosphino)ethyl]amine), coexisting in the later case with a square-pyramidal arrangement, react with one equivalent of CuCl to give the mononuclear heteroionic systems [M(L)Cl](CuCl₂) [L = PNHP, M = Pd (1a); L = P₃, M = Pd (2a), Pt (3a); L = NP₃, M = Pt (5a)]. The crystal structure of 3a confirms that Pt(II) retains the distorted square-planar geometry of 3 in the cation with P₃ acting as tridentate chelating ligand, the central P atom being trans to one chloride. The counter anion is a nearly linear dichlorocuprate(I) ion. However, the five-coordinate complexes [Pd(NP₃)Cl]Cl (4), [M(PP₃)Cl]Cl (M = Pd (6), Pt (7); PP₃ = tris[2-(diphenylphosphino)ethyl] phosphine) containing three fused five-membered chelate rings undergo a ring-opening by interaction with one (4, 6, 7) and two (6, 7) equivalents of CuCl with formation of neutral MCu(L)Cl₃ [L = NP₃, M = Pd (4a); L = PP₃, M = Pd (6a), Pt (7a)] and ionic [MCu(PP₃)Cl₂](CuCl₂) [M = Pd (6b), Pt (7b)] compounds, respectively. The heteronuclear systems were shown by ³¹P NMR to have structures where the phosphines are acting as tridentate chelating ligands to M(II) and monodentate bridging to Cu(I). Further additions of CuCl to the neutral species 6a and 7a in a 1:1 ratio resulted in the achievement of the ionic complexes 6b and 7b with ions as counter anions. It was demonstrated that the formation of heterobimetallic or just mononuclear mixed salt complexes was clearly influenced by the polyphosphine arrangement with the tripodal ligands giving the former compounds. However, complexes [M(NP₃)Cl]Cl constitute one exception and the type of reaction undergone versus CuCl is a function of the d⁸ metal centre.     

Synthesis and characterisation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes [Ti(IV), Zr(IV), Hf(IV), La(III), Ce(III), Yb(III), Sn(II) and Fe(II)]

The preparation of a series of 1,2-phenylenedioxoborylcyclopentadienyl-metal complexes is described. These are of formula [M{η⁵-C₅H₄(BX)}Cl₃] [M = Ti and X = CAT (2a), CAT^t (2b) or CAT^tt (2c); X = CAT^tt and M = Zr (4a) or Hf (4b)], [M{η⁵-C₅H₄(BX)}₂Cl₂] [M = Zr, X = CAT (3a) or CAT^t (3c); or M = Hf, X = CAT (3b) or CAT^t (3d)], [M{(μ-η⁵-C₅H₃BCAT)₂ SiMe₂}Cl₂] [M = Zr (5a) or Hf (5b)], [M{η⁵-C₅H₃(BCAT)₂}Cl₃] [M = Zr (6a) or Hf (6b)], [M{η⁵-C₅H₄BCAT}₃(THF)] [M = La (7a), Ce (7b) or Yb (7c)], [Sn{η⁵-C₅ H₄(BCAT^t)}Cl](8) and [Fe{η⁵-C₅H₄(BCAT^t)}₂] (9). The abbreviations refer to BO₂C₆H₄-1,2 (BCAT) and the 4-Bu^t (BCAT^t) and the (BCAT^tt) analogues. The compounds 2a-9 have been characterised by microanalysis, multinuclear NMR and mass spectra. The single crystal X-ray structure of the lanthanum compound 7a is presented.     

Syntheses of Group 14 bis(tert-butylamido)cyclodiphosph(III)azane dichlorides, and the solid-state structures of the silicon and tin derivatives

To test the synthetic utility of bis(tert-butylamido)cyclodiphosph(III)azanes as ligands we extended the coordination chemistry of these diamides from Group 4 to Group 14. The syntheses of compounds of the formula cis-[^tBuNP(μ-^tBuN)₂PN^tBu]ECl₂, E = Si (1), Ge (2), Sn (3) and the solid-state structures of 1 and 3 are reported. Silicon tetrachloride reacted with dilithiobis(tert-butylamido)cyclodiphosph(III)azane to cleanly produce cis-[^tBuNP(μ-^tBuN)₂PN^tBu]SiCl₂, but for the germanium and tin analogues the interaction of GeCl₄ or SnCl₄ with the diazastannylene cis-[^tBuNP(μ-^tBuN)₂PN^tBu]Sn proved to be a better method. Single-crystal X-ray studies on both 1 and 3 revealed that they had C_s-symmetric structures, the central element being coordinated by two amide nitrogens and two chlorides, in addition to being weakly coordinated by one of the cyclodiphosph(III)azane ring nitrogens. Using structural comparisons between crystallographically-independent 1a and 1b, between 1 and 3, and between 3 and its isomorphous zirconium analogue, the nature of this donor bond is discussed.     

Synthesis, characterization, crystal structure and antitumor activity of organotin(IV) compounds bearing ferrocenecarboxylic acid

Four new organotin(IV) complexes [(Bu₃Sn)(FcCOO)]_n (1), [(μ-Bu₂Sn)₂(μ-Bu₂SnFcCOO)₂(μ₃-O)₂(μ-OCH₃)₂]₂ (2), [Ph₃Sn(FcCOO)(H₂O)](phen) (3) and [{Ph₃Sn(FcCOO)}₂(4,4′-bipy)] (4) [Fc = (η⁵-C₅H₅)Fe(η⁵-C₅H₄)] have been synthesized and characterized by elemental analyses, IR, (¹H and ¹³C) NMR spectra and X-ray single-crystal diffraction analyses. The structure analyses show that all tin atoms in complexes 1-4 are five-coordinated with trigonal bipyramid geometry. Complexes 1-4 and FcCOOH undergo reversible one-electron oxidations in methanol solution. The antitumor activities of complexes 1-4 have also been tested. Complexes 1 and 2 exhibit medium activity towards P388 cell lines and Hela cell lines. Complexes 3 and 4 exhibit medium activity towards P388 cell lines but strong activity towards Hela cell lines. This may result from complexes 3 and 4 including the neutral molecules 1,10-phenanthroline and 4,4′-bipy.     

Multimetallic compounds containing cyclometalated Ir(III) units: Synthesis, structure, electrochemistry and photophysical properties

The reaction of the cyclometalated Ir^III dimer [{(ppy)₂Ir}₂(μ-Cl)₂] (ppyH = 2-phenylpyridine) with silver triflate followed by a multidentate ligand [1,4-bis[3-(2-pyridyl)pyrazolylmethyl]benzene (bppb), 1,3,5-tri[3-(2-pyridyl)pyrazolylmethyl]-2,4,6-trimethylbenzene (tppb), 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), 2-chloro-4,6-bis(dipyridin-2-ylamino)-1,3,5-triazine (cddt) or 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (tdat)] afforded di- or trinuclear compounds: [{Ir(ppy)₂}₂(μ-bppb)](OTf)₂ (1), [{Ir(ppy)₂}₃(μ-tppb)](OTf)₃ (2), [{Ir(ppy)₂}₂(μ-tptz-OH)](OTf) (3), [{Ir(ppy)₂}₂(μ-cddt)](OTf)₂ (4) and [{Ir(ppy)₂}₂(μ-tdat)](OTf)₂ (5). All of these compounds contain cationic metal cores with corresponding triflate counter anions. The molecular structures of 1-4 reveal that the structural feature of the Ir(ppy)₂ center of the starting precursor is conserved in the products. Also, because of the nature of the ligands, there is virtually no electronic communication between the Ir^III centers except in 3 where a ring hydroxylation at the triazine carbon atom is effected upon metalation. Compounds 1-5 are robust in solution where they retain their structural integrity. The UV-Vis and emission spectra of 1-5 compounds are very similar to each other with the exception of 3 which seems to possess a different electronic structure. All the compounds are luminescent at room temperature. The emission bands indicate significant contribution from ³LC. Increase in the number of ‘Ir(ppy)₂’ units does not have any effect on emission color.     

Synthesis and reactivity of osmium (VI) nitrido complexes containing pyridine-carboxylato ligands

A series of osmium(VI) nitrido complexes containing pyridine-carboxylato ligands Os^VI(N)(L)₂X (L = pyridine-2carboxylate (1), 2-quinaldinate (2) and X = Cl (a), Br (1b and 2c) or CH₃O (2b)) and [Os^VI(N)(L)X₃]⁻ (L = pyridine-2,6-dicarboxylate (3) and X = Cl (a) or Br (b)) have been synthesised. Complexes 1 and 2 are electrophilic and react readily with various nucleophiles such as phosphine, sulfide and azide. Reaction of Os^VI(N)(L)₂X (1 and 2) with triphenylphosphine produces the osmium(IV) phosphiniminato complexes Os^VI(NPPh₃)(L)₂X (4 and 5). The kinetics of nitrogen atom transfer from the complexes Os^VI(N)(L)₂Br (2c) (L = 2-quinaldinate) with triphenylphosphine have been studied in CH₃CN at 25.0 °C by stopped-flow spectrophotometric method. The following rate law is obtained: −d[Os(VI)]/dt = k₂[Os(VI)][PPh₃]. Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) reacts also with [PPN](N₃) to give an osmium(III) dichloro complex, trans-[PPN][Os^III(L)₂Cl₂] (6). Reaction of Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) with lithium sulfide produces an osmium(II) thionitrosyl complex Os^II(NS)(L)₂Cl (7). These complexes have been structurally characterised by X-ray crystallography.