Luminescent homoleptic bismuth(III) complexes have been synthesized by adding several functionalized 8-hydroxyquinolate ligands to bismuth(III) chloride in a 3:1 mole ratio in either ethanol or tetrahydrofuran (THF) solvent. These complexes have been characterized by single-crystal X-ray diffraction (XRD) analysis, UV-vis spectroscopy, fluorescence spectroscopy, and density functional theory (DFT) calculations to determine their structures and photophysical properties. Reversible dimerization of the mononuclear tris(hydroxyquinolate) complexes was observed in solution and quantified using UV-vis spectroscopy. The fluorescence spectra show a blue shift for the monomer compared with homoleptic aluminum(III) hydroxyquinolate compounds. Four dimeric compounds and one monomeric isomer were characterized structurally. The bismuth(III) centers in the dimers are bridged by two oxygen atoms from the substituted hydroxyquinolate ligands. The more sterically hindered quinolate complex, tris(2-(diethoxymethyl)-8-quinolinato)bismuth, crystallizes as a monomer. The complexes all exhibit low-lying absorption and emission spectral features attributable to transitions between the HOMO (π orbital localized on the quinolate phenoxide ring) and LUMO (π* orbital localized on the quinolate pyridyl ring). Excitation and emission spectra show a concentration dependence in solution that suggests that a monomer-dimer equilibrium occurs. Electronic structure DFT calculations support trends seen in the experimental results with a HOMO-LUMO gap of 2.156 eV calculated for the monomer that is significantly larger than those for the dimers (1.772 and 1.915 eV). The close face to face approach of two quinolate rings in the dimer destabilizes the uppermost occupied quinolate π orbitals, which reduces the HOMO-LUMO gap and results in longer wavelength absorption and emission spectral features than in the monomer form.

The title cluster, which was obtained serendipitously when (η5-C5H5)Co(PPh3)2 was added to a (η5-C5H5)Co metallacyclobutene containing a sulfone group, is the largest cluster known, formed primarily with (η5-C5H5)Co vertices. The closo-(η5-C5H5Co)5S is a closed-shell, octahedral cluster which forms black, monoclinic crystals from methanol.

The title iron(II) complex, [Fe(C16H12NO2)2], crystallizes in the ortho-rhom-bic space group Pbca with the Fe(2+) cation positioned on an inversion center. The cyclo-penta-dienyl (Cp) rings adopt an anti conformation in contrast with other substituted ferrocenes in which the Cp rings appear in a nearly eclipsed conformation. The Cp and the aromatic rings are positioned out of the plane, with a twist angle of 70.20 (12)°, and the C(Cp)-C(CO) bond length is shorter than a typical C-C single bond, which suggests a partial double-bond character and delocalization with the Cp π system. The structure of the complex is compared to other functionalized ferrocenes synthesized in our laboratory.

The title compound, C24H18N4S3, exhibits three near planar benzo-thia-zole systems in a pseudo-C 3 conformation. The dihedral angles between the planes of the benzo-thia-zole groups range from 112.56 (4) to 124.68 (4)° In the crystal, mol-ecules are connected to each other through three short C-H⋯N contacts, forming an infinite chain along [100]. The molecules are also linked by π-π interactions with each of the three five-membered thiazole rings. [inter-centroid distance range: 3.614 (1)-4.074 (1) Å, inter-planar distance range: 3.4806 (17)-3.6902 (15) Å, slippage range: 0.759 (3)-1.887 (3) Å].

Off-cycle processes in catalytic reactions can dramatically influence the outcome of the chemical transformation and affect its yield, selectivity, rate, and product distribution. While the generation of off-cycle intermediates can complicate reaction coordinate analyses or hamper catalytic efficiency, the generation of such species may also open new routes to unique chemical products. Recently, we reported the Pd-mediated functionalization of carboranes with a range of O-, N-, and C-based nucleophiles. By utilizing a Pd-based catalytic system supported by a biaryl phosphine ligand developed by Buchwald and co-workers, we discovered an off-cycle isomerization process ("cage-walking") that generates four regioisomeric products from a single halogenated boron cluster isomer. Here we describe how several off-cycle processes affect the regioisomer yield and distribution during Pd-catalyzed tandem cage-walking/cross-coupling. In particular, tuning the transmetallation step in the catalytic cycle allowed us to incorporate the cage-walking process into Pd-catalyzed cross-coupling of sterically unencumbered substrates, including cyanide. This work demonstrates the feasibility of using tandem cage-walking/cross-coupling as a unique low-temperature method for producing regioisomers of mono-substituted carboranes.

A systematic study of arene-perfluoroarene interactions in solution is presented. Using a combination of NMR titration experiments, X-ray crystallography, and computational analysis, we analyze the effects of fluorination, substituents, ring size, and solvation on the arene-perfluoroarene interaction. We find that fluorination, extension of the π systems, and enhancement of solvent polarity greatly stabilize the stacking energy up to 3 orders of magnitude (K_a = <1 to 6000 M^-1), with the highest K_a achieved for the interaction of water-soluble variants of perfluoronaphthalene and anthracene in buffered D₂O (pD = 12). Combining computational and experimental results, we conclude that this impressive binding energy is a result of enthalpically favorable electrostatic and dispersion interactions as well as the entropically driven hydrophobic effect. The enhanced understanding of arene-perfluoroarene interactions in aqueous solution sets the stage for the implementation of this abiotic intermolecular interaction in biology and medicine.

The reaction of (η5-C5H5)Co(PPh 3)2 with TMSCC(CO2Et) leads to the formation of the cobalt-alkyne complex (η5-C5H5) (PPh3)Co{η2-(Me3Si)CC(CO2Et)} (6). In benzene-d6 solution containing PPh3, 6 undergoes slow conversion to the cobaltacyclopentadiene complex (η5-C 5H5)(PPh3)Co{κ2-(TMS) CC(CO2Et)C(TMS)C(CO2Et)} (7, TMS = SiMe3). Alternatively, reaction of 6 and PhCCPh forms the metallacyclopentadiene regioisomers (η5-C5H5)(PPh 3)Co{κ2-(R1)CC(R2)C(Ph) =C(Ph)} [9-major, R1 = SiMe3, R2 = CO2Et; 9-minor, R1 = CO2Et, R2 = SiMe3). The metallacycle substitution pattern in 9-major and 9-minor is readily deduced from the 1H NMR spectral resonances of the diastereotopic ethoxycarbonyl hydrogens. When the diastereotopic hydrogens of the ethoxycarbonyl have similar chemical shifts the ester is situated on the β-carbon of the metallacycle. When the methylene hydrogens give rise to well-separated resonances the ethoxycarbonyl is situated on the α-carbon of the metallacycle. The solid state structures of 7 and 9-major were determined by X-ray crystallography. © 2013 Elsevier B.V. All rights reserved.

A series of 19 different asymmetric catalysts were screened in an effort to identify the first chiral catalyst for the rearrangement of α-hydroxy imines to α-amino ketones involving a 1,2-carbon shift. Although aluminate complexes of VAPOL, VANOL, and 7,7'-(t)Bu2VANOL were quite effective catalysts giving up to 88% ee, the ne plus ultra catalyst for this reaction was found to be a zirconium complex of VANOL which gives 97 to >99% ee for the majority of the substrates examined. An X-ray diffraction study of the catalyst reveals that the zirconium exists as a homoleptic complex with three VANOL ligands and two protonated N-methyl imidazoles.

Cp'₂Ln(THF)₂ metallocenes (Cp' = C₅H₄SiMe₃) react with 2.2.2-cryptand (crypt) to form Ln²⁺-in-crypt complexes, [Ln(crypt)(THF)][Cp'₃Ln]₂ (Ln = Sm, Eu) and [Yb(crypt)][Cp'₃Yb]₂, that contain Ln²⁺ ions surrounded only by neutral ligands. A bimetallic, mixed-ligand metallocene/opened-crypt complex of Sm²⁺, [Sm(C₁₆H₃₂N₂O₆-κ²O:κ²O')SmCp''₂], was obtained by KC₈ reduction of Cp''₂Sm(THF) [Cp'' = C₅H₃(SiMe₃)₂] in the presence of crypt.