Luminescent complexes of iridium(III) containing N/\C/\N-coordinating terdentate ligands

A family of bis-terdentate iridium(III) complexes is reported which contain a cyclometalated, N/\C[wedge]N-coordinating 1,3-di(2-pyridyl)benzene derivative. This coordination mode is favored by blocking competitive cyclometalation at the C4 and C6 positions of the ligand. Thus, 1,3-di(2-pyridyl)-4,6-dimethylbenzene (dpyxH) reacts with IrCl3 x 3H2O to generate a dichlorobridged dimer [Ir(dpyx-N,C,N)Cl(mu-Cl)]2, 1. This dimer is cleaved by DMSO to give [Ir(dpyx)(DMSO)Cl2], the X-ray crystal structure of which is reported here, confirming the N/\C/\N coordination mode of dpyx. The dimer 1 can also be cleaved by a variety of other ligands to generate novel classes of mononuclear complexes. These include charge-neutral bis-terdentate complexes of the form [Ir(N/\C/\N)(C/\N/\C)] and [Ir(N/\C/\N)(C/\N/\O)], by reaction of 1 with C/\N/\C-coordinating ligands (e.g., 2,6-diphenylpyridine and derivatives) and C/\N/\O-coordinating ligands (based on 6-phenylpicolinate), respectively. Treatment of 1 with terpyridines leads to dicationic complexes of the type [Ir(N/\C/\N)(N/\N/\N)]2+, while 2-phenylpyridine gives [Ir(dpyx-N/\C/\N)(ppy-C,N)Cl]. All of the charge-neutral complexes are luminescent in fluid solution at room temperature. Assignment of the emission to charge-transfer excited states with significant MLCT character is supported by DFT calculations. In the [Ir(N/\C/\N)(C/\N/\C)] class, fluorination of the C/\N/\C ligand at the phenyl 2' and 4' positions leads to a blue-shift in the emission and to an increase in the quantum yield (lambda(max) = 547 nm, phi = 0.41 in degassed CH(3)CN at 295 K) compared to the nonfluorinated parent complex (lambda(max) = 585 nm, phi = 0.21), as well as to a stabilization of the compound with respect to photodissociation through cleavage of mutually trans Ir-C bonds. [Ir(dpyx-N/\C/\N)(ppy-C,N)Cl] is an exceptionally bright emitter: phi = 0.76, lambda(max) = 508 nm, in CH(3)CN at 295 K. In contrast, the [Ir(N/\C/\N)(C/\N/\O)] complexes are much less emissive, shown to be due to fast nonradiative decay of the excited state, probably involving reversible Ir-O bond cleavage. The [Ir(N/\C/\N)(N/\N/\N)]2+ complexes are very feeble emitters even at 77 K, probably due to the almost exclusively interligand charge-transfer nature of the lowest-energy excited state in these complexes.     

Ethylene polymerization and ethylene/hexene copolymerization by vanadium(III) complexes bearing bidentate phenoxy‐phosphine oxide ligands

A series of novel vanadium(III) complexes bearing bidentate phenoxy‐phosphine oxide [O,P=O] ligands, (2‐R₁‐4‐R₂‐6‐Ph₂P=O‐C₆H₂O)VCl₂(THF)₂ ( 2a : R₁ = R₂ = H; 2b : R₁ = F, R₂ = H; 2c : R₁ = tBu, R₂ = H; 2d : R₁ = Ph, R₂ = H; 2e : R₁ = R₂ = Me; 2f : R₁ = R₂ = tBu; 2g : R₁ = R₂ = CMe₂Ph) have been synthesized by adding 1 equiv of the ligand to VCl₃(THF)₃ dropwise in the presence of excess triethylamine. Under the same conditions, the adding of VCl₃(THF)₃ to 2.0 equiv of the ligand afforded vanadium(III) complexes bearing two [O,P=O] ligands ( 3c , 3f ). All the complexes were characterized by FTIR and mass spectra as well as elemental analysis. Structures of complexes 2c and 3c were further confirmed by X‐ray crystallographic analysis. On activation with Et₂AlCl and ethyl trichloroacetate, these complexes displayed high catalytic activities for ethylene polymerization (up to 26.4 kg PE/mmol_V·h·bar) even at high reaction temperature (70 °C) indicative of high thermal stability, and produced high molecular weight polymers with unimodal molecular weight distributions. Additionally, the complexes with optimized structure exhibited high catalytic activities for ethylene/1‐hexene copolymerization. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled in a wide range via the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and reaction temperature. The monomer reactivity ratios r_E and r_H were determined according to ¹³C NMR spectra, which indicated these complexes preferred ethylene to 1‐hexene in the copolymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5298–5306     

Synthesis,structural characterization,and olefin polymerization behavior of vanadium(III) complexes bearing bidentate phenoxy‐phosphine ligands

Vanadium(III) complexes bearing phenoxy‐phosphine ligands ( 2a–g ) (2‐R₁‐4‐R₂‐6‐PPh₂‐C₆H₂O)VCl₂(THF)₂ ( 2a : R₁ = R₂ = H; 2b : R₁ = F, R₂ = H; 2c : R₁ = Ph, R₂ = H; 2d : R₁ = tBu, R₂ = H; 2e : R₁ = R₂ = Me; 2f : R₁ = R₂ = tBu; 2g : R₁ = R₂ = CMe₂Ph) were prepared from VCl₃(THF)₃ by treating with 1.0 equiv of the ligand in tetrahydrofuran (THF) in the presence of excess triethylamine (TEA). The reaction of VCl₃(THF)₃ with 2.0 equiv of the ligand in THF in the presence of excess TEA afforded vanadium(III) complexes bearing two phenoxy‐phosphine ligands ( 3c–f ). These complexes were characterized by FTIR and mass spectrum as well as elemental analyses. Structures of 2f and 3c were further confirmed by X‐ray crystallographic analyses. Complexes 2a–g and 3c–f were employed as the catalysts for ethylene polymerization under various reaction conditions. On activation with Et₂AlCl, these complexes exhibited high catalytic activities (up to 41.3 kg PE/mmol_V·h·bar) even at high temperature (70°C), and produced high molecular weight polymer with unimodal molecular weight distributions, indicating the polymerization took place in a single‐site nature. Complexes 3c–f displayed better thermal stability than the corresponding complexes 2a–g under similar conditions. In addition, copolymerizations of ethylene and 1‐hexene with precatalysts 2a–g were also explored in the presence of Et₂AlCl. Catalytic activity, comonomer incorporation, and properties of the resultant polymers can be controlled over a wide range by tuning catalyst structures and reaction parameters.© 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Rhodium(I) carbonyl complexes with heterocyclic and nonheterocyclic nitrogen-donor ligands

Summary Complexes of the [Rh(N-N)(CO)₂][RhCl₂(CO)₂], [Rh(N-N)(CO)₂]BF₄ and Rh(N-N)(CO)₂Cl types where (N-N) = 2,9-dimethyl-1,10-phenanthroline (Me₂Phen), 4,7-diphenyl-1,10-phenanthroline (Ph₂Phen), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (Me₂2Ph₂Phen) or 2,2-biquinoline (biq), have been prepared and investigated. Benzidine (benz) ando-tolidine (tol) also form complexes of the first type. The complexes of the first two types behave as 11 electrolytes. While Ph₂Phen forms the four coordinate monocarbonyl Rh(Ph₂Phen)(CO)Cl complex, benzo(f)-quinoline (Q) yields the Rh(CO)₂ (Q)Cl compound. Triphenyl-phosphine and triphenylarsine react with the above complexes to form the well knowntrans-Rh(CO)ClL₂ where L = PPh₃ or AsPh₃. The i.r. and u.v.-visible spectra of the compounds are discussed.     

Insulin-enhancing vanadium(III) complexes

Simple, high-yield, large-scale syntheses of the V(III) complexes tris(maltolato)vanadium(III), V(ma)3, tris(ethylmaltolato)vanadium(III), V(ema)3, tris(kojato)vanadium(III) monohydrate, V(koj)3-H2O, and tris(1,2-dimethyl-3-hydroxy-4-pyridinonato)vanadium(III) dodecahydrate, V(dpp)3-12H2O, are described; the characterization of these complexes by various methods and, in the case of V(dpp)3-12H2O, by an X-ray crystal structure determination, is reported. The ability of these complexes to normalize glucose levels in the STZ-diabetic rat model has been examined and compared with that of the benchmark compound BMOV (bis(maltolato)oxovanadium(IV)), an established insulin-enhancing agent.     

Enhanced lasing properties of dissymmetric Eu(III) complex with bidentate phosphine ligands

The luminescent and lasing properties of Eu(III) complexes were enhanced by using an dissymmetric Eu(III) complex. The photophysical properties (the emission spectral shapes, the emission lifetimes, the emission quantum yields, and the stimulated emission cross section (SEC)) were found to be dependent on the geometrical structures of Eu(III) complexes. The geometrical structures of Eu(III) complexes were determined by X-ray single crystal analyses. The symmetrical group of Eu(hfa)3(BIPHEPO) (tris(hexafluoroacetylacetonato)europium(III) 1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide)) was found to be C1, which was more dissymmetric than Eu(hfa)3(TPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry) and Eu(hfa)3(OPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry). The analytical data were supported by Judd-Ofelt analysis. The most dissymmetrical Eu(III) complex, Eu(hfa)3(BIPHEPO), showed large electron transition probability and large SEC (4.64 x 10(-20) cm2). The SEC of Eu(hfa)3(BIPHEPO) was superior to even the values of Nd-glass laser for practical use (1.6-4.5 x 10(-20) cm2). The lasing properties of Eu(III) complexes in polymer thin film were measured by photopumping of a Nd:YAG laser (355 nm). The threshold energy of lasing oscillation was found to be 0.05 mJ. The increasing rate of the lasing intensity of Eu(hfa)3(BIPHEPO) as a function of the excitation energy was much larger than that of Eu(hfa)3(TPPO)2 and Eu(hfa)3(OPPO)2. The dissymmetrical structure of Eu(hfa)3(BIPHEPO) promoted the enhancement of the lasing property.     

The spin-states and spin-transitions of mononuclear iron(II) complexes of nitrogen-donor ligands

A survey of mononuclear iron(II) complexes with heterocyclic N-donor ligation is presented. A brief introduction to spin-crossover chemistry and low-temperature spin-trapping is provided, since many of these compounds undergo thermal spin-transitions upon cooling or heating. These are highlighted, and the structural changes underlying spin-crossover are discussed where this is known. Materials showing spin-trapping behaviour following thermal quenching or irradiation at very low temperatures are also described.     

Synthesis, characterisation and X-ray structures of diorganotin(IV) and iron(III) complexes of dianionic terdentate Schiff base ligands

Diorganotin(IV) complexes, [SnR₂L] (1)-(4), (R = Me, Ph), of the terdentate Schiff bases N-[(2-pyrroyl)methylidene]-N′-tosylbenzene-1,2-diamine (H₂L¹) and N-[(2-hydroxyphenyl)metylidene]-N′-tosylbenzene-1,2-diamine (H₂L²) have been synthesised. The complexes were obtained by addition of the appropriate ligand to a methanol suspension of the corresponding diorganotin(IV) dichloride in the presence of triethylamine. However, the reaction between the precursor [η⁵-C₅H₅Fe(CO)₂]₂SnCl₂ and the Schiff bases in the presence of triethylamine gave (5) and (6), respectively. The crystal structures of the ligands and complexes have been studied by X-ray diffraction. The structure of [SnR₂L] complexes shows the tin to be five-coordinate in a distorted square pyramidal environment with the dianionic ligand acting in a terdentate manner. In 5 and 6, the iron atom is in a slightly distorted octahedral environment and is meridionally coordinated by two ligands. Spectroscopic data for the ligands and complexes (IR, ¹H, ¹³C and ¹¹⁹Sn NMR and mass spectra) are discussed and related to the structural information.     

Chromium(III) complexes with terdentate 2,6-bis(azolylmethyl)pyridine ligands: Synthesis, structures and ethylene polymerization behavior

Reactions of 2,6-bis(bromomethyl)pyridine with 3,5-dimethylpyrazole and 1H-indazole yield the terdentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (5) and 2,6-bis(indazol-2-ylmethyl)pyridine (6). The molecular structure of the new compound 6 was determined by single-crystal X-ray diffraction. These ligands react with the CrCl₃(THF)₃ complex in THF to form neutral complexes of general formula [CrCl₃{2,6-bis(azolylmethyl)pyridine-N,N,N}] (7, 8) which are isolated in high yields as stable green solids and characterized by means of elemental analysis, magnetic moments, IR, and mass spectroscopy. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active in the polymerization of ethylene.     

Crystal structures of (azido)(pentamethylcyclopentadienyl)iridium(III) complexes containing various types of bidentate ligands

Several (azido)iridium(III) complexes having a pentamethylcyclopentadienyl (Cp∗) group, [Cp∗Ir(N₃)₂(Ph₂Ppy-κP)] (1: Ph₂Ppy = 2-diphenylphosphinopyridine), [Cp∗Ir(N₃)(Ph₂Ppy-κP,κN)]CF₃SO₃ (2), [Cp∗Ir(N₃)(dmpm)]PF₆ (3: dmpm = bis(dimethylphosphino)methane), [Cp∗Ir(N₃)(Ph₂Pqn)]PF₆·$·$CH₃OH (4·$·$CH₃OH: Ph₂Pqn = 8-diphenylphosphinoquinoline), and [Cp∗Ir(N₃)(pybim)] (5: Hpybim = 2-(2-pyridyl)benzimidazole) have been prepared and their crystal structures have been analyzed by X-ray diffraction. In complex 1, the Ph₂Ppy ligand is only coordinated via the P atom (-κP), while in 2 it acts as a bidentate ligand through the P and N atoms (-κP,κN) to form a four-membered chelate ring. Comparing the structural parameters of the chelate ring in 2 with those of a similar five-membered chelate ring formed by Ph₂Pqn in 4, it became apparent that the angular distortion in the Ph₂Ppy-κP,κN ring was remarkable, although the Ir–P and Ir–N bonds in the Ph₂Ppy-κP,κN ring were not elongated very much from the corresponding bonds in the Ph₂Pqn-κP,κN ring. In the pybim complex 5, the five-membered chelate ring was coplanar with the pyridine and benzimidazolyl rings. With the related (azido)iridium(III) complexes analyzed previously, comparison of the structural parameters of the Ir–N₃ moiety in [Cp∗Ir^III(N₃)(L–L′)]^+/0 complexes reveals an anomalous feature of the 2,2′-bipyridyl (bpy) complex, [Cp∗Ir(N₃)(bpy)]PF₆.     

Synthesis and characterization of triorganoantimony(V) complexes with bidentate ligands

Monochelated organoantimony(V) complexes of the type R₃Sb(OMe)L, where R = Me or Ph, and L is the anion of acetylacetone, 8-hydroxyquinoline, salicylaldehyde, o-hydroxyacetophenone or 2-hydroxy-1-naphthaldehyde have been obtained from triorganoantimony(V) dibromide and the sodium derivative of the ligands in a benzene-methanol mixture. Molecular weight determination in benzene reveals the monomeric nature of these complexes. IR and NMR data suggest that L acts as a bidentate ligand giving an octahedral environment for the antimony atom.     

Ethylene homopolymerizaton and copolymerizaton by vanadium(III) complexes containing tridentate or tetradentate iminopyrrolyl ligands

Iminopyrrolyl vanadium(III) complexes 2a–b bearing tridentate ligands [C₄H₃NCH?NC₆H₄L]VCl₂(THF) [L = 2‐P(C₆H₅)₂ ( 2a ), 2‐SMe ( 2b )] and complexes 2c–d with tetradentate ligands [(C₄H₃NCH?N)₂R]VCl(THF) [R = 1,2‐C₆H₄ ( 2c ), 1,2‐C₂H₄ ( 2d )] have been synthesized in high yields. With diethylaluminium chloride as a cocatalyst, complexes 2a–d were investigated as efficient catalysts for ethylene polymerization under various reaction conditions, and exhibited high catalytic activity and remarkable thermal stability. With these complexes, high molecular weight polymers with unimodal molecular weight distributions were obtained, indicating that the polymerization reaction took place in a single‐site nature. Ethylene/1‐hexene copolymerizations were also investigated in the presence of Et₂AlCl. Both increasing ligand denticity and introducing softer atom into the sidearm of the ligands significantly influenced catalytic activity, comonomer incorporation, and the molecular weights of the resultant polymers, suggesting that both the steric and the electronic effects of the ligands played an important role in adjusting chain propagation and transfer rate. The chain transfer mechanisms involved in the copolymerization process were investigated by carefully analyzing the microstructure of the copolymers. The signals of vinyl, disubstituted and tri‐substituted vinylene double bond end groups were detected in the copolymer obtained by 2a /Et₂AlCl system but not in those by 2b–c /Et₂AlCl systems, indicating that bulky electron‐donating group, ? P(C₆H₅)₂, may lead to those unusual transfer reactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Luminescense properties of new complexes of Eu(III) and Tb(III) with heterotopic ligands

As a result of coordination between ligands L and L' and europium(III) and terbium(III) ions, the new architectures were formed. The formulae of the complexes have been assigned on the basis of the spectroscopic data in solution and microanalyses. The europium complexes show excellent luminescence properties with high quantum yield (1b-Eu(3)L(2)) and effective intramolecular energy transfer from the ligand to the Eu(III) ions.     

On the origin of circular dichroism in trigonal dihedral cobalt (III) complexes of unsaturated bidentate ligands

The circular dichroism spectra of the complexes Co(acac)3, [Co(ox)3]3-, [Co(mal)3]3-, and [Co(Thiox)3]3- with acac=acetylacetonate, ox=oxalate, mal=malonate, Thiox=dithioxalate, have been investigated computationally employing time-dependent density functional theory. A detailed comparison of the experimental and theoretical results is made. Rotatory strengths associated with typical electronic transitions in the complexes containing unsaturated ligands are interpreted within a qualitative framework in terms of transition moments for excitations within a single ligand.     

Trimethylplatinum(IV) complexes with ON bidentate ligands

Complexes of the trimethylplatinum(IV) moiety with bidentate monobasic salicylaldimines C₆H₅(OH)CHNR (R = ethyl, propyl, phenyl) have been prepared and characterized by IR, UV and NMR spectra and magnetic susceptibility measurements. The complexes are dimeric with double PtOPt bridges, and the metal appears to be pseudo-octahedrally hexacoordinated.     

Vanadium(IV) and vanadium(V) complexes of salicyladimine ligands

The synthesis and characterization of a V(IV) and a V(V) complex of the salicyladimine ligand system are described. The reaction of salicylaldehyde and 1,3-diaminohydroxypropane with vanadyl sulfate produced a monomer (VOL1) which, upon heating in methanol, crystallized as a V(V) complex (VO(2)L1). The reaction of 3-methoxysalicylaldehyde, 1,3-diaminohydroxypropane, and vanadyl sulfate resulted in a binuclear complex held together by hydrogen bonding (VOL2). VOL1 was determined to catalyze the epoxidation of cyclohexene better than VOL2. The synthesis and characterization of VOL1, VOL2, and VO(2)L1 are described. The role of each complex as a catalyst for the epoxidation of cyclohexene is investigated. Results indicate that the V(V) complex performs better than either of the V(IV) complexes.     

Heteroligand copper(II) complexes with hydroxyethyleneiminodiacetic acid and bidentate nitrogen-containing ligands: Structures and properties

Procedures were proposed for the synthesis of the heteroligand copper(II) complexes with N-(2-hydroxyethyl)iminodiacetic acid (H₂Heida) and 2-aminoethanol and ethylenediamine ligands. The optimal parameters of solutions for the isolation of ternary complexes were found. Heteroligand complexes Cu(Heida)En · 3H₂O (I) and Cu(Heida)Mea (II) (En is ethylenediamine, and Mea is 2-aminoethanol) were examined by X-ray diffraction analysis. The thermal properties of complexes I and II and their thermodynamic stability in aqueous solutions were studied.     

A trigonal-bipyramidal oxorhenium(V) complex with a bidentate nitrogen-donor ligand

The oxorhenium(V) complex [ReO(Hapb)(apb)] (1) (H₂apb =?2-(2-aminophenyl)-1-benzimidazole) was prepared by reaction of trans-[ReO₂(py)₄]Cl with a twofold molar amount of H₂apb. The complex was characterized by spectroscopy and X-ray crystallography. The results show that the rhenium atom lies in a distorted trigonal-bipyramidal environment, with the two imidazole nitrogen atoms in apical positions, and the oxo and two amido nitrogens in the trigonal plane.