James B. Updegraff

Homoleptic, Four-Coordinate Azadipyrromethene Complexes of d10 Zinc and Mercury

Tetraarylazadipyrromethenes, and especially their boron chelates, are a growing class of chromophores that are photoactive toward red light. The coordination chemistry of these ligands remains to be explored. Reported here are four-coordinate zinc(II) and mercury(II) complexes of tetraarylazadipyrromethene ligands. The new complexes contain two azadipyrromethenes bound per d(10) metal center and are characterized by (1)H NMR, optical absorption spectroscopy, X-ray diffraction crystallography, and elemental analysis. Solid-state structures show that these bis-chelate complexes distort significantly from idealized D2d symmetry. AM1 geometry optimizations indicate relaxation energies in the range of 6.8-15.2 kcal mol(-1); interligand pi-stacking provides an added energetic impetus for distortion. The absorption spectra show a marked increase in the absorption intensity in the red region and, in the case of the zinc(II) complexes, the development of a second distinct absorption band in this region, which is red-shifted by ca. 40-50 nm relative to the free ligand. Semiempirical INDO/S computations indicate that these low-energy optical absorptions derive from allowed excitations among ligand-based orbitals that derive from the highest occupied molecular orbital and lowest unoccupied molecular orbital of the free azadipyrromethene.

Synergistic Binding of Both Lewis Acids and Bases to Phosphinidenes

Free phosphinidenes or phosphanylidenes (RP), the heavier analogues of carbenes, remain unisolable owing to their extreme reactivity. Although a significant body of stable transition metal complexes having terminal PR functionalities now exists, simple main group adducts of phosphinidenes are by comparison rare. Phosphanylidene-s-phosphoranes (RP= PR’3) are a fundamental type of base-stabilized adducts of phosphinidenes First recognized in 1961 with the synthesis of CF3P=PMe3, [3] and later studied in more detail, these early derivatives were thermally unstable and not structurally characterized. Derivatives bearing additional phosphorus atoms and lone pairs, such as R2P P=P(X)R’2 are also an important class of such materials, and they have received attention as phosphinidene precursors and transfer reagents. 5] The more recent discovery of thermally stable ArP=PR3, where Ar is a sterically demanding aryl group, allowed for structural identification and more detailed studies. Phosphanylidene-s-phosphoranes can be pictorially represented by various resonance forms (Scheme 1, top)

Constrained Digold(I) Diaryls: Syntheses, Crystal Structures, and Photophysics

A series of di(gold(I) aryls), L(AuR)(2) (L = DPEphos, DBFphos, or Xantphos; R = 1-naphthyl, 2-naphthyl, 9-phenanthryl, or 1-pyrenyl), have been prepared. The complexes were characterized by multinuclear NMR spectroscopy, static and time-dependent optical spectroscopy, mass spectrometry, microanalysis, and X-ray crystallography. In addition, DFT calculations on model dinuclear gold complexes have been used to examine the electronic structures. Photophysical properties of the dinuclear complexes have been compared to mononuclear analogues. Low-temperature excited-state lifetimes for both the mononuclear and dinuclear complexes in toluene indicate triplet-state emission. Time-resolved DFT calculations suggest that emission originates from aryl-ligand transitions, even if the LUMO resides elsewhere.

Three-Coordinate, Phosphine-Ligated Azadipyrromethene Complexes of Univalent Group 11 Metals

Tetraarylazadipyrromethenes are Lewis basic, red-light absorbing dyes with optical properties conducive to sensing and therapeutic applications. Recently, transition metal complexes of these ligands have been described. Here, we report a series of three-coordinate Group 11 complexes of unsubstituted and methoxy-substituted tetraarylazadipyrromethenes. In each, two pyrrole nitrogens chelate a d(10) metal ion; triphenyl- or triethylphosphine occupies a third coordination site. New complexes are characterized by multinuclear NMR, X-ray crystallography, optical absorption and emission spectroscopy, and elemental analysis. Solid-state structures show trigonal planar geometries about the metal centers, and reveal pervasive intra- and intermolecular pi-stacking interactions. Visible light absorption intensifies with metal binding, in some cases shifting to longer wavelengths. The complexes weakly luminesce in the red region; emission wavelengths and quantum yields are similar to those of free azadipyrromethenes. Methoxy-substitution on the ligand red-shifts optical features, whereas substitution of triethylphosphine for triphenylphosphine in the third coordination site has minimal structural or spectral consequences.

Gold(I) halide complexes of bis(diphenylphosphine)diphenyl ether ligands: a balance of ligand strain and non-covalent interactions

A series of bis(gold(I) halide; halide = Cl, Br, I) complexes of di(phosphino)diphenyl ether derivatives (L = DPEphos, DBFphos, Xantphos, tBuXantphos) have been synthesized. The new complexes have been characterized by X-ray crystallography, multinuclear NMR, and elemental analysis. The compounds luminesce at room temperature in dichloromethane solution. Many such complexes undergo aurophilic Au...Au bonding, and have chiral structures as a result. In complexes of the tBuXantphos ligand, X-ray crystallography indicates that an ion pair forms where the diphosphine ligand chelates one gold atom, and the other is part of an [AuX(2)](-) counterion (X = Cl, Br, I). It appears that the observed conformations of the metal-coordinated ligands are a balance of ligand strain and non-covalent interactions, including aurophilicity, intramolecular pi-stacking, halide-halide repulsion, and intramolecular Au-O interactions. Together with previous investigations, this research shows that Xantphos and its derivatives form a robust set of coordination complexes with gold that are stable in air and amenable to further synthetic manipulation. It is anticipated that these materials will be suitable precursors for gold-carbon coupling reactions and gold-based catalysis.

Azido, Triazolyl, and Alkynyl Complexes of Gold(I): Syntheses, Structures, and Ligand Effects

Gold(I) triazolyl complexes are prepared in [3 + 2] cycloaddition reactions of (tertiary phosphine)gold(I) azides with terminal alkynes. Seven such triazolyl complexes, not previously prepared, are described. Reducible functional groups are accommodated. In addition, two new (N-heterocyclic carbene)gold(I) azides and two new gold(I) alkynyls are described. Eight complexes are crystallographically authenticated; aurophilic interactions appear in one structure only. The packing diagrams of gold(I) triazolyls all show intermolecular hydrogen bonding between N-1 of one molecule and N-3 of a neighbor. This hydrogen bonding permeates the crystal lattice. Density-functional theory calculations of (triphenylphosphine)gold(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger trans-influencer than is the alkynyl, but the alkynyl is more electron-releasing. These results suggest that trans-influences in two-coordinate gold(I) complexes can be more than a simple matter of ligand donicity.

N-(9H-Fluoren-9-ylidene)-N-(-2-methoxy- phenyl)amine

Department of Chemistry, YoungstownState University, One University Plaza,Youngstown, Ohio 44555-3663, USACorrespondence e-mail:crundwellg@mail.ccsu.eduKey indicatorsSingle-crystal X-ray studyT = 100 KMean ˙(C–C) = 0.002 A˚R factor = 0.051wR factor = 0.139Data-to-parameter ratio = 17.9For details of how these key indicators wereautomatically derived from the article, seehttp://journals.iucr.org/e.# 2004 International Union of CrystallographyPrinted in Great Britain – all rights reserved

4-Bromo­thio­phene-2-carbox­aldehyde

The title compound, C4H3BrOS, (I), was recrystallized from ethanol at 273 K. The crystal structure of (I) has been determined at 100 K.

Redetermination of 9-nitroanthracene at 100 K

The title compound, C14H9NO2, was synthesized by the electrophilic aromatic substitution reaction between anthracene and nitric acid. The crystal structure is a low-temperature (100 K) redetermination of a previously reported room-temperature structure [Trotter (1959). Acta Cryst. 12, 237–242].