Synthesis, structural characterization and the first electroluminescent properties of tris- and bis-cycloiridiated complexes of sterically hindered electron-poor 2-(3,5-bis(trifluoromethyl)phenyl)-4-trifluoromethylpyridine

An application of the new sterically hindered electron-poor 2-(3,5-bis(trifluoromethyl)phenyl)-4-trifluoromethylpyridine [HC--N] (1) in the one-step high temperature cyclometalation by Ir(III)Cl3 in the presence of Ag(I)OC(O)CF3 resulted in the synthesis of tris-cyclometalated complexes [C--N]2Ir[C--C] (3) and [C--N]3Ir (5). A neutral silver cluster with a repeating unit of hexa-silver groups in an infinite chain of (2) was isolated from the above reaction as well. When this cyclometalation was carried out in trimethylphosphate at lower temperature, bis-cyclometalated derivatives [C--N]2Ir(mu-Cl)2Ir[CN]2 (6), [C--N]2Ir[eta2-(O(C((t)Bu))2CH] (7), and [C--N]2Ir(mu-O-P(OMe)2-O)2Ir[C--N]2 (8) were synthesized. According to X-ray analyses complex (3), while trivalent, contains four cyclometalated single Ir-C bonds. One of the Ir-C bonds, next to the nitrogen atom of the CC pyridinium ligand, was found to be the shortest to date (1.977(4) angstroms) for a single bond between iridium and carbon atoms. The coordination of the C--C ligand in (3) to iridium has a decidedly interesting bonding pattern and can be explained by various formulations. The first one is considering this ligand as a monoanionic chelating ligand, in which the second coordination site arises from a carbene or azomethine ylide. Overall the best single picture may be a dianionic ligand making two normal Ir-C bonds, in which the ligand just happens to contain a pyridinium function that compensates for one negative charge on the iridium. LEDs constructed with compounds (7) and (8) give blue-green emission with peak electroluminescent efficiency of 15 and 2 cd A(-1), respectively. An LED constructed with compound (5) gives a yellowish emission with peak electroluminescent efficiency of 5.5 cd A(-1).     

High‐temperature catalysts for the production of α‐olefins based on iron(II) and iron(III) tridentate bis(imino)pyridine complexes modified by nitrilo group

Series of Fe(II) and Fe(III) tridentate bis(imino)pyridine complexes without nitrilo groups 2–6 and with nitrilo groups 7–13 were synthesized. According to X‐ray analysis, the introduction of nitrilo groups in para‐ and ortho‐positions tends to result in shorter axial Fe? N bonds. Both types of complexes, 2–6 and 9–13 , afforded very productive catalysts for the production of α‐olefins with higher K values and better linearity of Schultz–Flory distribution α‐olefins than the parent methyl substituted Fe(II) complex 1 . Noticeably, the complexes functionalized with a para‐nitrilo group 9–13 tend to make α‐olefins with higher K values of the Schultz–Flory distribution, more ideal distributions, and less of the heavier insoluble fractions of α‐olefins than corresponding nonsymmetrically substituted complexes without para‐nitrilo groups 2–6 . Statistically significant correlations were obtained between % solids of total α‐olefins and the blocked solid angle fraction in the +z hemisphere ( = 51.3%, p = 0.012) and between catalyst productivity and total blocked solid angle fraction ( = 43.5%, p = 0.023). The modest values of show that, while steric effects are significant, they are not the sole factor determining catalyst performance. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 585–611, 2008     

A stabilized beta-oxaphosphoniumbetaine: an elusive zwitterion

A beta-oxaphosphoniumbetaine stabilized by two tert-butyl groups at the phosphonium part of the betaine and two trifluoromethyl groups at the carbon adjoined to the oxa part of the betaine was isolated and structurally characterized. Additional stabilization results from the solvation of the betaine by a parent phosphonium salt, as in 4, or by protonation with methanol, as in 10. According to X-ray analysis, the betaine exhibits a sterically strained "gauche" conformeric form, with torsion angles in the P-C-C-O moiety of 32.2 degrees for 4 and 28.1 degrees for 10. The P...O separations of 3.121 A for 4 and 3.086 A for 10 are just under the sum of the O and P van der Waals radii (3.32 A). The fast H/D exchange of alpha hydrogen atoms to the phosphonium center was observed in the solution of 10 in deuterium oxide and MeOH-d4. The beta-oxaphosphoniumbetaine has long been suspected as an intermediate in the Wittig reaction, but this is the first time a stabilized derivative has been isolated.     

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.     

High precision delta(17)O isotope measurements of oxygen from silicates and other oxides: method and applications

The use of infrared laser-assisted fluorination to release oxygen from milligram quantities of silicates or other oxide mineral grains is a well-established technique. However, relatively few studies have reported the optimisation of this procedure for oxygen-17 isotope measurements. We describe here details of an analytical system using infrared (10 μm) laser-assisted fluorination, in conjunction with a dual inlet mass spectrometer of high resolving power ( approximately 250) to provide (17)O and (18)O oxygen isotope measurements from 0.5-2 mg of silicates or other oxide mineral grains. Respective precisions (1) of typically 0.08 and 0.04 per thousand are obtained for the complete analytical procedure. Departures from the mass-dependent oxygen isotope fractionation line are quantified by Delta(17)O; our precision (1) of such measurements on individual samples is shown to be +/-0.024 per thousand. In turn, this permits the offset between parallel, mass-dependent fractionation lines to be characterised to substantially greater precision than has been possible hitherto. Application of this system to investigate the (17)O versus (18)O relationship for numerous terrestrial whole-rock and mineral samples, of diverse geological origins and age, indicates that the complete data set may be described by a single, mass-dependent fractionation line of slope 0.5244+/- 0.00038 (standard error). Copyright 1999 John Wiley & Sons, Ltd.     

A novel pattern of dimerization for 1, 4‐diphospha‐1,3‐butadienes

A new example of [2+4] cycloaddition of the low‐coordinated diphospha‐analog of butadiene protected with a 2,4‐di‐tert‐butyl‐6‐methylphenyl group has been described. X‐ray structure investigations of monomer 4b and dimer 5a have been reported for the first time. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:231–234, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10123     

2,4,6‐Tri‐tert‐butylphenyl and 2,4‐di‐tert‐butyl‐6‐methylphenyl groups: Look similar,react differently

The crystal structures of molecules with two phosphaalkene groups have been determined. Differences in the stabilization of the PC π‐bond by the 2,4,6‐tri‐tert‐butylphenyl and 2,4‐di‐tert‐butyl‐6‐methylphenyl groups were observed. It has been found that lithium supermesityl(trimethylsilyl)phosphide could be a very efficient base to remove a proton from acetonitrile.© 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:662–666, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10083     

Effect of the relaxation of high-frequency vibrational modes on the kinetics of charge separation and recombination

The processes of intramolecular electron transfer from the second excited electron state accompanied by superfast reverse transfer to the first excited state are studied. The kinetics of the populations of the first and second excited states, along with that the charge-separated states, is calculated within the generalized stochastic model, taking into account the reorganization of the medium and intramolecular high-frequency vibrations. It is shown that variations in the relaxation rate of the high-frequency vibrational modes can change the population of the quenching products by a factor of two to three. It is established that in the case of the weak exothermicity of the charge separation process, the population of the charge-separated states declines upon an increase in the vibrational relaxation rate, while the population of the first excited state increases; in the region of high exothermicity, these dependences change to ones that are opposite. To reveal the scales of these effects in real systems, the kinetics of the photo-induced processes in the zinc-porphyrin derivatives, including electron-acceptor imide groups covalently coupled with porphyrin rings, are calculated. It is shown that the results from calculating the kinetics of the population of the first and the second excited states agree well with the experimental data on the kinetics of the fluorescence of these states. The absolute values of the population of the charge-separated state and the first excited state are determined. The key role of the hot electron transitions that occur in parallel with the relaxation of the medium and intramolecular vibrations in the considered process is shown.     

Test of bell’s inequality using the one-atom micromaser

We examine a local realist bound in the case of a one-atom micromaser. It is shown that such a bound is violated using a simplified treatment of the micromaser. We consider the effect of dissipation in a proposed experiment with the real micromaser. It is seen that the magnitude of violation of a Bell-type inequality depends significantly on the cavity parameters.     

Reaction of phenyl azide with N,N-dimethyl-aminomethylenephenylphosphines

Phenyl azide reacts with N,N-dimethylamino-P-phenylmethylenephosphines with cleavage of the phosphoruscarbon double bond and formation of the dimer of diiminophosphorane and amidines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2381–2382, October, 1989.