Synthesis and structural chemistry of bis(pyridylimino)isoindolato-ruthenium complexes and their activity as mediators in the atom transfer radical polymerization (ATRP) of styrene

The reaction of the Bispyridyl Isoindole (BPI) type ligands L1 and L2 (L1 = 1,3-Bis(2-(4-tert-butylpyridyl)imino) isoindole, L2 = 1,3-Bis(2-(5-bromo)imino)-5,6-dimethylisoindole) with [Ru(μ-Cl)₂(cod)]_x in presence of triethylamine using coordinating solvents like acetonitrile, dimethyl sulfoxide or pyridine cleanly gave the complexes [{BPI(L1,L2)}Ru^II(Cl)(S)₂] (L1: S = acetonitrile (1), dimethyl sulfoxide (2), pyridine (3); L2: S = acetonitrile (4), dimethyl sulfoxide (5), pyridine (6)). In these complexes the BPI ligands meridionally coordinated to the ruthenium center as established by X-ray diffraction for complexes 3 and 6. The catalytic activity in the direct ATRP (Atom Transfer Radical Polymerization) of styrene was tested for complexes 1-6.     

Synthesis, characterization, and cyclometalation studies of benzo[1,2-h: 5,4-h′]diquinolines with palladium and platinum

Benzo[1,2-h: 5,4-h′]diquinoline(1a) represents a new family of tridentate NCN pincer ligand. We report the synthesis of the parent ligand (1a) and its derivatives (1b R = Me, 1c R = t-Butyl, 1d R = Phenyl). The ligands were characterized by ¹H and ¹³C NMR, as well as mass spectral analysis, and X-ray structural determination. They readily undergo cyclometalation with LiPdCl₄, Pd(OAc)₂, and K₂PtCl₄ to form the cyclometalated Pd(NCN)Cl (2a-c, 3a), and Pt(NCN)Cl (4a) pincer complexes. These complexes have been characterized through NMR, and mass spectrometry. PdNCNCl (2a) structure was determined by single crystal X-ray diffraction. Complex 2a has shown to catalyze the Heck coupling reaction between bromobenzene and n-butylacyrlate in NMP at 140 °C, TON of 2506 were observed.     

Synthesis, characterization and in vitro DNA binding studies of tin(IV) complexes of tert-butyl 1-(2-hydroxy-1-phenylethylamino)-3-methyl-1-oxobutan-2-yl carbamate

Tin(IV) complexes 1(a and b) and 2(a and b) of valine derived peptide derivatives were synthesized and characterized on the basis of elemental analysis, IR, ¹H, ¹³C, ¹¹⁹Sn NMR, ESI-MS spectra and molar conductance measurements. The C-Sn-C angle was estimated from ^I3C and ¹H NMR data ¹J(¹¹⁹Sn, ^I3C) = 623 Hz; solution ²J(¹¹⁹Sn, ¹H) = 93.04 Hz to be 149.9°. In vitro binding studies of complexes 1 and 2 under physiological conditions at room temperature with CT-DNA were carried out employing UV-visible, fluorescence, circular dichroism and viscometric studies. The binding affinity of the complexes was quantified by calculating the K_b values and it follows the order 2a > 1a > 2b > 1b. To further examine the specific mode of binding, the interaction of complexes 2(a and b) were carried out with 5′GMP and 5′TMP by using absorption and NMR (¹H, ³¹P) spectroscopy. The supercoiled pBR322 plasmid DNA cleavage activity of the complexes was ascertained by gel electrophoresis assay. The complexes cleave supercoiled pBR322 plasmid DNA efficiently into its nicked form at micromolar concentrations.     

A cyclometalated diplatinum complex containing 1,1′-bis(diphenylphosphino)ferrocene as spacer ligand: Antitumor study

Cyclometalated platinum(II) complex [Pt(C^N)Cl(dmso)], 1, in which C^N = N(1),C(2′)-chelated deprotonated 2-phenylpyridine and dmso = dimethylsulfoxide, was reacted with 1 equiv of 1,1′-bis(diphenylphosphino)ferrocene, dppf, to give the cyclometalated diplatinum(II) complex [Pt₂(C^N)₂Cl₂(μ-dppf)], 2, along with 0.5 equiv of unreacted dppf. However, the related reaction with 0.5 equiv of dppf produced complex 2 in pure form. Complex 2 in solution was fully characterized by using multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, and ¹⁹⁵Pt) and a number of 2D NMR experiments. The structure of complex 2 in solid state was determined by X-ray crystallography showing that the bridging dppf ligand is arranged close to “antiperiplanar staggered” conformation. Cytotoxicity of the complex 2 was studied in three human cancer cell lines derived from ovarian carcinoma(CH1), lung carcinoma(A549), and colon carcinoma (SW480) by means of the MTT assay (MTT = 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide).     

Synthesis, characterization and spectroscopic studies of cyclometalated platinum(II) complexes containing meta-bis(2-pyridoxy)benzene

A series of mononuclear and binuclear cyclometalated platinum(II) complexes containing new terdentate meta-bis(2-pyridoxy)benzene ligands: 3,5-bis(2-pyridoxy)toluene (L₁H) and 3,5-bis(2-pyridoxy)-2-dodecylbenzene (L₂H): [Pt(L₁)Cl] (1), [Pt(L₂)Cl] (2), [Pt(L₁)(CH₃CN)](ClO₄) (3), {[Pt(L₁)]₂(μ-dppm)}(ClO₄)₂ (4), {[Pt(L₂)]₂(μ-dppm)}(ClO₄)₂ (5), {[Pt(L₁)]₂(μ-pyrazole)}(ClO₄) (6), {[Pt(L₂)]₂(μ-pyrazole)}(ClO₄) (7), {[Pt(L₁)]₂(μ-imidazole)}(ClO₄) (8) and {[Pt(L₂)]₂(μ-imidazole)}(ClO₄) (9), have been synthesized and characterized. These ligands are coordinated to platinum(II) in a “pincer”-like manner and the presence of pyridyl donors enhances the availability of the ligand π^∗ orbitals for electronic transition. Spectroscopic properties of these cyclometalated complexes were studied. While the non-coplanar nature of the ligands hinders ligand-ligand and metal-metal interactions in these cyclometalated complexes, the presence of long hydrocarbon side chain on ligand L₂H seems to alleviate such hindrance. Intermolecular π-π, and possibly Pt-Pt interactions were observed in complex 2 at high concentration.     

Synthesis and characterization of half-sandwich Rh, Ir complexes containing mono-thiolate-ortho-carborane ligand

Two binuclear complexes [Cp^∗M(Cl)Carb^S]₂ (Cp^∗ = η⁵-C₅Me₅, M = Rh (1a), Carb^S = SC₂(H)B₁₀H₁₀, Ir (1b)) were synthesized by the reaction of LiCarb^S with the dimeric metal complexes [Cp^∗MCl(μ-Cl)]₂ (M = Rh, Ir). Four mononuclear complexes Cp^∗M(Cl)(L)Carb^S (L = BuⁿPPh₂, M = Rh (2a), Ir (2b); L = PPh₃, M = Rh (4a), Ir (4b)) were synthesized by reactions of 1a or 1b with L (L = BuⁿPPh₂ (2); PPh₃ (4)) in moderate yields, respectively. Complexes 3a, 3b, 5a, 5b were obtained by treatment of 2a, 2b, 4a, 4b with AgPF₆ in high yields, respectively. All of these compounds were fully characterized by IR, NMR, and elemental analysis, and the crystal structures of 1a, 1b, 2a, 2b, 4a, 4b were also confirmed by X-ray crystallography. Their structures showed 3a, 3b and 5a, 5b could be expected as good candidates for heterolytic dihydrogen activation. Preliminary experiments on the dihydrogen activation driven by these half-sandwich Rh, Ir complexes were done under mild conditions.     

Osmium assisted C-H activation and CN cleavage of N-(2′-hydroxyphenyl) benzaldimines. Synthesis, structure and electrochemical properties of some organoosmium complexes

Reaction of N-(2′-hydroxyphenyl)-4-R-benzaldimines (L-R, R = OCH₃, CH₃, H, Cl and NO₂) with [Os(PPh₃)₃Br₂] in refluxing 2-methoxyethanol in the presence of triethylamine affords two families of organoosmium complexes (1-R and 2-R). In both 1-R and 2-R complexes a benzaldimine ligand is coordinated to the metal center as tridentate C,N,O-donor. In the 1-R complexes, a bidentate N,O-donor imionsemiquinonate ligand, derived from the hydrolysis of another benzaldimine, and a PPh₃ ligand are also coordinated to osmium. In the 2-R complexes, a carbonyl, derived from decarbonylation of 4-R-benzaldehyde (derived from the same hydrolysis stated above), and two PPh₃ ligands take up the remaining coordination sites on osmium. Structures of the 1-Cl and 2-OCH₃ complexes have been determined by X-ray crystallography. All the 1-R and 2-R complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the 1-R complexes shows a reversible Os(III)-Os(IV) oxidation within 0.47-0.67 V (vs SCE), followed by an irreversible oxidation of the imionsemiquinonate ligand within 1.10-1.36 V. An irreversible Os(III)-Os(II) reduction is also displayed by the 1-R complexes within −1.02 to −1.14 V. Cyclic voltammetry on the 2-R complexes shows a reversible Os(II)-Os(III) oxidation within 0.29-0.51 V, followed by a quasi-reversible oxidation within 1.04-1.29 V, and an irreversible reduction of the coordinated benzaldimine ligand within −1.16 to −1.31 V.     

Neutral penta-coordinated diorganotin(IV) complexes derived from ortho-aminophenol Schiff bases: Synthesis, characterization and molecular structures

The one pot reactions carried among ortho-aminophenol, R₂SnO (R = Me or Ph) and acetyl acetone, 2-hydroxyacetophenone and 2-hydroxy-3-methylacetophenone led to six new diorganotin(IV) compounds Me₂SnL1 (1), Ph₂SnL1 (2), Me₂SnL2 (3) Ph₂SnL2 (4), Me₂SnL3 (5) and Ph₂SnL3 (6) (H2L1 = 2-(3-hydroxy-1-methyl-but-2-enylideneamino)-phenol, H2L2 and H2L3 = 2-[1-(2-hydroxyaryl)alkylideneamino]-phenol) in good yields. Combination of IR, ¹H, ¹³C and ¹¹⁹Sn NMR and X-ray diffraction techniques along with elemental analyses evidenced the formation of penta-coordinated monomeric species. The crystal structures of ligand H2L1 and complexes 1, 3 and 4 were determined by single crystal X-ray diffraction study. In the solid state, the ligand H2L1 exists as keto-enamine tautomeric form. There are N-H…O intra-molecular hydrogen bonds between amine and carbonyl groups. Diorganotin(IV) complexes 1, 3 and 4 are monomers with TBP (trigonal bipyramidal) geometry surrounding the tin atom. The O, N, O- tridentate ligand places its two oxygen donating atoms in the axial positions, and the nitrogen atom occupies one equatorial position. The two R groups attached to tin occupy the other two equatorial positions. The solution structures were predicted by ¹¹⁹Sn NMR spectroscopy.     

From platina-β-diketones to diacetylplatinum(II) complexes - Synthesis, characterization and structural features

The reaction of the electronically unsaturated platina-β-diketone [Pt₂{(COMe)₂H}₂(μ-Cl)₂] (1a) with N^?N donors led to the formation of diacetyl(hydrido)platinum(IV) complexes [Pt(COMe)₂Cl(H)(N^?N)] (2). By the reaction of these complexes with NaOH in a two-phase system (H₂O/CH₂Cl₂) diacetylplatinum(II) complexes [Pt(COMe)₂(N^?N)] (N^?N = bpy, 4a; 4,4′-Me₂-bpy, 4b; 4,4′-t-Bu₂-bpy, 4c; 4,4′-Ph₂-bpy, 4d; 4,4′-t-Bu₂-6-n-Bu-bpy, 4e; bpym, 4f; bpyr, 4g; phen, 4h; 4-Me-phen, 4i; 5-Me-phen, 4j) were obtained. All complexes were characterized by microanalysis, IR and ¹H and ¹³C NMR spectroscopy. Additionally, complexes 4a, 4c, 4d and 4e were characterized by single-crystal X-ray diffraction analysis. The observed variety of packing patterns resulting from π-π stacking and hydrogen bonding is discussed.     

Chiral organotin (IV) carboxylates complexes: Syntheses, characterization, and crystal structures with chiral (S)-(+)-6-methoxy-α-methyl-2-naphthaleneaceto acid ligand

Eight new organotin (IV) carboxylates, (R₃Sn)₄(nap)₄ (R = Me 1, n-Bu 2), [(R₃Sn) (nap)]_n (R = Ph 3, PhCH₂4), (R₂Sn) (nap)₂ (R = n-Bu 5, Ph 6, PhCH₂7) and {[R₂Sn(nap)]₂O}₂ (R = Me 8) (nap = (S)-(+)-6-methoxy-α-methyl-2-naphthaleneaceto anion) have been synthesized. All of the complexes have been characterized by elemental analysis, FT-IR, NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. Among these complexes, complexes 1, 3, 5 and 8 were also characterized by X-ray crystallography diffraction analysis, and the data of X-ray crystallography diffraction indicated that complexes 1, 3 and 5 are new chiral organotin (IV) carboxylates complexes. The structural analyses show that complex 1 has a tetranuclear Sn₄O₈ macrocycle structure, complex 3 has a 1D spring-like chiral helical chain with a columnar channel, complex 5 possesses a dimer structure, and complex 8 has a supramolecular chainlike ladder structure through weak intermolecular non-covalent O^…O interactions.     

Cyclometalated Ir(III) complexes containing N-aryl picolinamide ancillary ligands

The reaction of the cyclometalated chloro-bridged iridium(III) dimer, [(ppy)₂ Ir(μ-Cl)]₂ (ppy - 2-phenyl pyridine) with N-aryl picolinamides (LH, LH-NO₂, LH-CH₃, LH-l, LH-F) resulted in the formation of neutral heteroleptic complexes [Ir(ppy)₂L] (1), [Ir(ppy)₂L-NO₂](2), [Ir(ppy)₂L-CH₃](3), [Ir(ppy)₂L-Cl](4) and [Ir(ppy)₂L-F] (5). These complexes contain a six-coordinate iridium with a 2C, 4N coordination environment. The N-aryl picolinamide ligands are deprotonated during complexation and the resulting amidates bind to iridium in a chelating manner (N, N). Optical spectroscopic studies revealed that the complexes 1-5 exhibited intense π→π^∗ absorptions in the ultraviolet region. In addition low energy transitions due to ¹MLCT, ¹LLCT and ³MLCT are also seen. The emission spectra of 1-5, upon excitation at 450 nm, show a single emission with a λ_max around 513 nm. The lifetimes of this emission are in between 7.4 and 9.6 μs while the quantum yields are quite high and range from 0.2 to 0.5. Based on density functional theory (DFT) calculations on 1 and 3, the three highest occupied orbitals are composed of ligand π orbitals mixed with Ir-d orbitals while the three lowest unoccupied orbitals are mostly π orbitals of the ligands. From the time dependent DFT calculations it is revealed that the lowest energy electronic singlet and triplet excitations are a mixture of MLCT and LLCT.     

Rhodium(I) carbonyl complexes of quinoline carboxaldehyde ligands and their catalytic carbonylation reaction

The dimeric rhodium precursor [Rh(CO)₂Cl]₂ reacts with quinoline (a) and its three isomeric carboxaldehyde ligands [quinoline-2-carboxaldehyde (b), quinoline-3-carboxaldehyde (c), and quinoline-4-carboxaldehyde (d)] in 1:2 mole ratio to afford complexes of the type cis-[Rh(CO)₂Cl(L)] (1a-1d), where L = a-d. The complexes 1a-1d have been characterised by elemental analyses, mass spectrometry, IR and NMR (¹H, ¹³C) spectroscopy together with a single crystal X-ray structure determination of 1c. The X-ray crystal structure of 1c reveals square planar geometry with a weak intermolecular pseudo dimeric structure (Rh?Rh = 3.573 Å). 1a-1d undergo oxidative addition (OA) with different electrophiles such as CH₃I, C₂H₅I and I₂ to give Rh(III) complexes of the type [Rh(CO)(COR)Cl(L)I] {R = -CH₃ (2a-2d), R = -C₂H₅ (3a-3d)} and [Rh(CO)Cl(L)I₂] (4a-4d) respectively. 1b exhibits facile reactivity with different electrophiles at room temperature (25 °C), while 1a, 1c and 1d show very slow reactivity under similar condition, however, significant reactivity was observed at a temperature ∼40 °C. The complexes 1a-1d show higher catalytic activity for carbonylation of methanol to acetic acid and methyl acetate [Turn Over Frequency (TOF) = 1551-1735 h⁻¹] compared to that of the well known Monsanto’s species [Rh(CO)₂I₂]⁻ (TOF = 1000 h⁻¹) under the reaction conditions: temperature 130 ± 2 °C, pressure 33 ± 2 bar, 450 rpm and time 1 h. The organometallic residue of 1a-1d was also isolated after the catalytic reaction and found to be active for further run without significant loss of activity.     

Fe Spin crossover materials based on dissymmetrical N4 Schiff bases including 2-pyridyl and 2R-imidazol-4-yl rings: Synthesis,crystal structure and magnetic and Mössbauer properties

The synthesis and characterization of new symmetrical Fe^II complexes, [FeL^A(NCS)₂] (1), and [FeL^Bx(NCS)₂] (2–4), are reported (L^A is the tetradentate Schiff base N,N′-bis(1-pyridin-2-ylethylidene)-2,2-dimethylpropane-1,3-diamine, and L^Bx stands for the family of tetradentate Schiff bases N,N′-bis[(2-R-1H-imidazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine, with: R = H for L^B1 in 2, R = Me for L^B2 in 3, and R = Ph for L^B3 in 4). Single-crystal X-ray structures have been determined for 1 (low-spin state at 293 K), 2 (high-spin (HS) state at 200 K), and 3 (HS state at 180 K). These complexes remain in the same spin-state over the whole temperature range [80–400 K]. The dissymmetrical tetradentate Schiff base ligands L^Cx, N-[(2-R₂-1H-imidazol-4-yl)methylene]-N′-(1-pyridin-2-ylethylidene)-2,2-R₁-propane-1,3-diamine (R₁ = H, Me; R₂ = H, Me, Ph), containing both pyridine and imidazole rings were obtained as their [FeL^Cx(NCS)₂] complexes, 5–10, through reaction of the isolated aminal type ligands 2-methyl-2-pyridin-2-ylhexahydropyrimidine (R₁ = H, 5–7) or 2,5,5-trimethyl-2-pyridin-2-ylhexahydropyrimidine (R₁ = Me, 8–10) with imidazole-4-carboxaldehyde (R₂ = H: 5, 8), 2-methylimidazole-4-carboxaldehyde (R₂ = Me: 6, 9), and 2-phenyl-imidazole-4-carboxaldehyde (R₂ = Ph: 7, 10) in the presence of iron(II) thiocyanate. Together with the single-crystal X-ray structures of 7 and 9, variable-temperature magnetic susceptibility and Mössbauer studies of 5–10 showed that it is possible to tune the spin crossover properties in the [FeL^Cx(NCS)₂] series by changing the 2-imidazole and/or C2-propylene susbtituent of L^Cx.     

Cobalt complexes of terpyridine ligands: Crystal structure and nuclease activity

Cobalt(II) (1) and cobalt(III) (2) complexes of tridentate ligand, imidazole terpyridine (Itpy), have been synthesized and characterized by both spectroscopic and electrochemical techniques. Single crystal X-ray diffraction studies of complexes 1 and 2 shows that the complexes belong to monoclinic crystal system, with the two Itpy ligands coordinated to the central metal ion. The binding behavior of both the cobalt complexes to calf thymus DNA has been investigated by UV–Vis, fluorescence spectroscopy, viscosity and electrochemical measurements. The results suggest that complexes 1 and 2 bind to DNA through intercalation. The intrinsic DNA binding constant values obtained from absorption spectral titration studies were found to be (5.07 ± 0.12) × 10³ M⁻¹ and (7.46 ± 0.16) × 10³ M⁻¹, respectively, for complexes 1 and 2. Gel electrophoresis studies with the cobalt complexes show that while complex 1 cleaves DNA in the presence of hydrogen peroxide, complex 2 cleaves DNA in the presence of ascorbic acid and hydrogen peroxide.     

Ruthenium piano-stool complexes containing mono- or bidentate pyrrolidinylalkylphosphines and their reactions with small molecules

Ruthenium piano-stool complexes incorporating the new bidentate aminoalkylphosphine ligand 1,2-bis(dipyrrolidin-1-ylphosphino)ethane (dpyrpe, I) or its monodentate counterpart bis(pyrrolidin-1-yl)methylphosphine (pyr₂PMe, II) have been prepared, [(C₅R₅)RuCl(PP)] (R = Me and PP = dpyrpe, 1; R = Me and PP = (pyr₂PMe)₂, 2; R = H and PP = dpyrpe, 3). Complexes 2 and 3 have been characterized by X-ray crystallography. Complexes 1 and 2 react with NaBAr₄^f in the presence of ligand L to yield [Cp^∗Ru(L)(dpyrpe-κ²P)][BAr^f₄] (L = MeCN, 4a; CO, 4b; N₂, 4c) and [Cp^∗Ru(L)(pyr₂PMe)₂][BAr₄^f] (L = MeCN, 5a; CO, 5b; N₂, 5c). Complex 4a was crystallographically characterized. The CO complexes 4b and 5b were examined using IR spectroscopy in an attempt to establish the electron-donating capabilities of I and II. Complex 1 oxidatively adds H₂ in the presence of NaBAr₄^f to yield the Ru(IV) dihydride [Cp^∗RuH₂(dpyrpe-κ²P)][BAr₄^f], 7.     

Pluri-dimensional hydrogen-bonded networks of novel thiophene-introduced oligo(imidazole)s and physical properties of their charge-transfer complexes with TCNQ

Novel π-extended oligo(imidazole)s composed of imidazole and thiophene ring systems, bis(imidazolyl)thiophenes 1-4, were synthesized as new building blocks for electron-donor molecules having diverse hydrogen-bonding directionalities in order to explore hydrogen-bonded charge-transfer complexes and supramolecular assemblies. The cyclic voltammetry of these compounds showed increase of electron-donating ability compared with those of 2,2′- and 4,4′-biimidazoles. In the crystal structure, 1, 2 and 3 exhibited multi-dimensional hydrogen-bonded networks via solvent molecules including the π-π interaction. Charge-transfer complexes of 1, 2 and 4 with TCNQ were characterized as partial charge-transfer complexes with segregated stacks. The compressed pellets of the TCNQ complex of 2 showed a high electrical conductivity (σ_rt=5.2×10⁻² S cm⁻¹) at room temperature with semiconducting behavior (activation energy, E_a=71 meV).     

Synthesis, structural characterization, and initial electroluminescent properties of bis-cycloiridiated complexes of 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine

A series of bis-cyclometalated Ir(III) complexes (8-10, 12, 15, 17, 19, 21, 23, 25, 28, 29 and 33) bearing two chromophoric N^∧C cyclometalated ligands derived from 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine (1) and a third nonchromophoric ligand has been synthesized. A palladium-catalyzed cross-coupling reaction between 2-chloro-4-methylpyridine (2) and 3,5-bis(trifluoromethyl)phenylboronic acid (3) was used to prepare 2-(3,5-bis(trifluoromethyl)phenyl)-4-methylpyridine (1). Cyclometalation of (1) by IrCl₃ was carried out in (MeO)₃PO, with the formation of chloro-bridged dimer [N^∧C]₂Ir(μ-Cl)₂Ir[C^∧N]₂ (8). Reaction of (8) with lithium 2,4-pentanedionate, lithium 2,2,6,6-tetramethyl-heptane-3,5-dionate (13), dipivaloyltrimethylsilylphosphine (14), 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octadione (16), 1,1,1,3,3,3-hexafluoro-2-pyridin-2-yl-propan-2-ol (18), 1,1,1,3,3,3-hexafluoro-2-pyrazol-1-ylmethyl-propan-2-ol (20), 2-diphenylphosphanylethanol (22), and 1-diphenylphosphanylpropan-2-ol (24), afforded octahedral iridium complexes 9, 12, 15, 17, 19, 21, 23 and 25, respectively. Complex 10, which contains three different ligands (L₁ = N^∧C of 1; L₂ = N^∧C of 4,4′-dimethyl-[2,2′]bipyridinyl 4; L₃ = O^∧O of 2,4-pentanedione), and complex 11, which contains no cyclometalated ligands (L₁ = 4; L₂ = L₃ = Cl; L₄ = O^∧O of 2,4-pentanedione) were also isolated as minor products in a one-pot reaction between a 94:5 mixture of 1 and 4, IrCl₃ and lithium 2,4-pentanedionate. Reaction of 8 with diphenylphosphanylmethanol (27) in 1,2-dichloroethane unexpectedly led to complexes 28 and 29. The reactions of 8 with benzoylformic acid resulted in the formation of hydroxyl-bridged dimer [N^∧C]₂Ir(μ-OH)₂Ir[C^∧N]₂ (33). According to X-ray analyses, Ir-to-Ir distances in the crystal cell increase from 6.86 Å for 10 to 13.31 Å for 33. The angle theta, which represents the twisting of two cyclometalated C-Ir-N planes relative to each other, varies from 97.5° for 21 to 90.76 for complex 28. OLED devices were fabricated from several Ir complexes and preliminary results are discussed.     

Influence of multidentate N-donor ligands on highly electrophilic zinc initiator for the ring-opening polymerization of epoxides

A set of multidentate ligands have been synthesized and used to stabilize the putative highly electrophilic zinc species initiating ring-opening polymerization (ROP) of cyclohexene oxide (CHO) and propylene oxide (PO). Reaction of the bidentate C₂-chiral bis(oxazoline) ligand (^R2,R3BOX: R₂ = (4S)-tBu, R₃ = H (a); R₂ = (4S)-Ph, R₃ = H (b); R₂ = (4R)-Ph, R₃ = (5S)-Ph (c)) with Zn(R₁)₂ (R₁ = Et (1), Me (2)) led to the heteroleptic three-coordinate complexes (^R2,R3BOX)ZnR₁, 1a-c and 2a, which were isolated in 92-96% yield. Next, two pyridinyl-functionalized N-heterocyclic carbene (NHC) ligands have been designed and synthesized: the 1,3-bis(2-pyridylmethyl)imidazolinium salt (d) and the protected NHC adduct 2-(2,3,4,5,6-pentafluorophenyl)-1,3-bis(2-pyridylmethyl)imidazolidine (e). The reaction of ligands d and e with ZnEt₂ led directly to the formation of (NHC)ZnEt(Cl) 3d complex with ethane elimination and the adduct (NHC-C₆F₅(H))ZnEt₂4e, respectively, in high yield. In situ combinations of selected complexes 1a-c, 3d and 4e with B(C₆F₅)₃ (1 or 2 equivalents) give active systems for ROP, with high productivity (3.3-5.9 10⁶ g_polym. mol_Zn⁻¹ h⁻¹) and high molecular weight (M_n up to 132 10³ g mol⁻¹) for CHO polymerization. Although the in situ B(C₆F₅)₃-activated zinc species were not isolated, the sterically demanding BOX ligands (1c > 1b > 1a) and functionalized NHC ligands seem to enhance the stability of highly electrophilic zinc complexes over ligand redistribution, allowing a better control of the cationic ROP as reflected particularly for 3d and 4e complexes by their respective efficiency (42-88%).     

Effect of ortho-substituents on the stereochemistry of 2-(o-substituted phenyl)-1H-imidazoline-palladium complexes

Palladium complexes composed of [Pd(Ln)₂Cl₂] (n = 1, 2, 3, 4, 6), [L5a]₂[PdCl₄] and [Pd(L5b)₂], where L1 = 4,5-dihydro-2-phenyl-1H-imidazole (=2-phenyl-1H-imidazoline), L2 = 2-(o-fluorophenyl)-1H-imidazoline, L3 = 2-(o-methylphenyl)-1H-imidazoline, L4 = 2-(o-tert-butylphenyl)-1H-imidazoline, L5a = 2-(o-hydroxyphenyl)-1H-imidazolinium, L5b = 2-(1H-imidazolin-2-yl)phenolate, and L6 = 2-(o-methylphenyl)-1H-imidazole, were synthesized. Molecular structures of the isolated palladium complexes were characterized by single crystal X-ray diffraction analysis. The effect of ortho-substituents on the phenyl ring on trans-chlorine geometry was noted for complexes [Pd(L1)₂Cl₂] 1a and 1b, [Pd(L2)₂Cl₂] 2 and [Pd(L6)₂Cl₂] 6, whereas cis-chlorine geometry was observed for [Pd(L3)₂Cl₂] 3 and [Pd(L4)₂Cl₂] 4. PdCl₂ reacts with 2-(o-hydroxyphenyl)-1H-imidazoline in DMF to give [L5a]⁺ and [L5b]^- so that [L5a]₂[PdCl₄] 5a and [Pd(L5b)₂] 5b were obtained. In complex 5b, as an N,O-bidentate ligand, two ligands L5b coordinated with the central Pd(II) ion in the trans-form. The coordination of PdCl₂ with 2-(o-hydroxyphenyl)-1H-imidazolines in solution was investigated by NMR spectroscopy.