Casey R. Wade

Fluoride Ion Complexation and Sensing Using Organoboron Compounds

Fluoride is often added to drinking water and toothpaste because of its beneficial effects in dental health. It is also administered in the treatment of osteoporosis.1 While the beneficial effects of fluoride are well documented, chronic exposure to high levels of this anion can lead to dental or even skeletal fluorosis.2-4 Taking into account these adverse effects, a great deal of attention has been devoted to the discovery of improved analytical methods for the detection of fluoride, especially in water. This field of research has also been stimulated by the potential use of such methods for the detection of phosphorofluoridate nerve agents such as Sarin or uranium hexafluoride, which release fluoride upon hydrolysis. In addition to these applications, the capture of fluoride, especially in water, is a stimulating academic challenge because of the high hydration enthalpy of this anion (∆H° ) -504 kJ mol-1). * To whom correspondence should be addressed. E-mail: simon.aldridge@ chem.ox.ac.uk (S.A.) and francois@tamu.edu (F.P.G.). † Texas A&M University. ‡ University of Oxford. Casey Wade was born in 1983 in Lynch, Nebraska. He earned a B.S. degree from the University of NebraskasLincoln in 2006. During his time there, he worked as an undergraduate researcher under the supervision of J. A. Belot and participated in a joint research internship at the American Air Liquide Chicago Research Center. In 2007, he joined the group of F. P. Gabbaı̈ at Texas A&M University, where he currently studies anion recognition using main group Lewis acids.

High Electrical Conductivity in Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, a Semiconducting Metal–Organic Graphene Analogue

Reaction of 2,3,6,7,10,11-hexaaminotriphenylene with Ni(2+) in aqueous NH3 solution under aerobic conditions produces Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), a new two-dimensional metal-organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm(-1), respectively, both records for MOFs and among the best for any coordination polymer.

Sensing of Aqueous Fluoride Anions by Cationic Stibine–Palladium Complexes

Turn on the lantern! The stibine donor ligand of a cationic palladium complex acts as a Lewis acid and reacts with a fluoride anion to afford the corresponding fluorostiboranyl-palladium species (see scheme). Bindung of the fluoride anion to the antimony center induces a change in denticity of the triphosphine unit and leads to a bright-orange trigonal-bipyramidal d(8) lantern complex.

Synthesis, Structure, and Properties of a T-Shaped 14-Electron Stiboranyl-Gold Complex

A cyclic stiboranyl-gold complex (1) supported by two 1,8-naphthalenediyl linkers has been synthesized and structurally characterized. The gold atom of this complex adopts a T-shaped geometry and is separated from the antimony center by only 2.76 Å. Surprisingly, the trivalent gold atom of this complex is involved in an aurophilic interaction, a phenomenon typically only observed for monovalent gold complexes. This phenomenon indicates that the stiboranyl ligand possesses strong σ-donating properties making the trivalent gold atom of 1 electron rich. This view is supported by DFT calculations as well as Au L(3)- and Sb K-edge XANES spectra which reveal that 1 may also be described as an aurate-stibonium derivative. In agreement with this view, complex 1 shows no reactivity toward the halides Cl(-), Br(-), and I(-). It does, however, rapidly react with F(-) to form an unprecedented anionic aurate fluorostiborane complex ([2](-)) which has been isolated as the tetra-n-butylammonium salt. The increased coordination number of the antimony center in this anionic complex ([2](-)) does not notably affect the Au-Sb separation (2.77 Å) or the geometry at the gold atom which remains T-shaped.

Improved Catalytic Activity and Stability of a Palladium Pincer Complex by Incorporation into a Metal–Organic Framework

A porous metal-organic framework Zr6O4(OH)4(L-PdX)3 (1-X) has been constructed from Pd diphosphinite pincer complexes ([L-PdX](4-) = [(2,6-(OPAr2)2C6H3)PdX](4-), Ar = p-C6H4CO2(-), X = Cl, I). Reaction of 1-X with PhI(O2CCF3)2 facilitates I(-)/CF3CO2(-) ligand exchange to generate 1-TFA and I2 as a soluble byproduct. 1-TFA is an active and recyclable catalyst for transfer hydrogenation of benzaldehydes using formic acid as a hydrogen source. In contrast, the homogeneous analogue (t)Bu(L-PdTFA) is an ineffective catalyst owing to decomposition under the catalytic conditions, highlighting the beneficial effects of immobilization.

Redox and anion exchange chemistry of a stibine-nickel complex: writing the L, X, Z ligand alphabet with a single element.

According to the covalent bond classification (CBC) method, two-electron donors are defined as L-type ligands, one-electron donors as X-type ligands, and two-electron acceptors as Z-type ligands. These three ligand functions are usually associated to the nature of the ligating atom, with phosphine, alkyl, and borane groups being prototypical examples of L-, X- and Z-ligands, respectively. A new SbNi platform is reported in which the ligating Sb atom can assume all three CBC ligand functions. Using both experimental and computational data, it is shown that PhICl2 oxidation of (o-(Ph2P)C6H4)3SbNi(PPh3) (1) into [(o-(Ph2P)C6H4)3ClSb]NiCl (2) is accompanied by a conversion of the stibine L-type ligand of 1 into a stiboranyl X-type ligand in 2. Furthermore, the reaction of 2 with the catecholate dianion in the presence of cyclohexyl isocyanide results in the formation of [(o-(Ph2P)C6H4)3(o-O2C6H4Sb)]Ni(CNCy) (4), a complex featuring a nickel atom coordinated by a Lewis acidic, Z-type, stiborane ligand.

Cyanide and Azide Anion Complexation by a Bidentate Stibonium-Borane Lewis Acid

Abstract Our ongoing interest in the chemistry of polyfunctional Lewis acids has led us to investigate the reaction of the stibonium-borane [o-(Ph2MeSb)(Mes2B)C6H4]+ (1+) with cyanide and azide, two toxic anions. Both anions react with 1+ to afford the corresponding neutral complexes 1-CN and 1-N3. Structural and computational studies show that the coordinated anion interacts with both the boron and antimony atoms of the bidentate Lewis acid. While the azide complex features a typical κ2N1 : N1 bridging azide ligand, the cyanide complex possesses a cyanoborate moiety whose cyanide interacts side-on with the stibonium center. The Lewis acid-anion interactions observed in these complexes have also been studied computationally using the Natural Bond Orbital method

Synthesis, structure and luminescence of 1,8-diaurionaphthalenes

Reaction of 1,8-dilithionaphthalene with [AuCl(Et3P)] or [Au2Cl2(μ-dppm)] (dppm = bis(diphenylphosphinomethane)) in Et2O/THF leads to formation of bis(triethylphosphine)-1,8-diaurionaphthalene (1) and dppm-1,8-diaurionaphthalene (2), respectively. The dppm ligand present in complex 2 bridges the two gold centers leading to formation of short intramolecular Au–Au distances of av. 2.85 A. Complex 2 reacts with AgPF6 in THF/CH2Cl2 to afford a dicationic Au4Ag2 complex which has been isolated as the bis(hexafluorophosphate) salt (3). In this cluster, two molecules of 2 sandwich two Ag cations resulting in the formation of a Au2AgAu2Ag six-membered ring in which the metal centers are connected by Au–Au (av. 2.84 A) and Au–Ag (av. 2.75 A) metallophilic interactions. This cluster is further stabilized by short Ag–C interactions involving some of the naphthalene carbon atoms. The luminescence spectra of 2 and 3 have been recorded. Both complexes display relatively broad emission bands centered at 540 nm which result, at least in part, from the heavy atom induced phosphorescence of the naphthalene chromophore.

Zirconium Metal–Organic Frameworks Assembled from Pd and Pt PNNNP Pincer Complexes: Synthesis, Postsynthetic Modification, and Lewis Acid Catalysis

Carboxylic acid-functionalized Pd and Pt PNNNP pincer complexes were used for the assembly of two porous Zr metal-organic frameworks (MOFs), 2-PdX and 2-PtX. Powder X-ray diffraction analysis shows that the new MOFs adopt cubic framework structures similar to the previously reported Zr6O4(OH)4[(POCOP)PdX]3, [POCOP = 2,6-(OPAr2)2C6H3); Ar = p-C6H4CO2-, X = Cl-, I-] (1-PdX). Elemental analysis and spectroscopic characterization indicate the presence of missing linker defects, and 2-PdX and 2-PtX were formulated as Zr6O4(OH)4(OAc)2.4[M(PNNNP)X]2.4 [M = Pd, Pt; PNNNP = 2,6-(HNPAr2)2C5H3N; Ar = p-C6H4CO2-; X = Cl-, I-]. Postsynthetic halide ligand exchange reactions were carried out by treating 2-PdX with Ag(O3SCF3) or NaI followed by PhI(O2CCF3)2. The latter strategy proved to be more effective at activating the MOF for the catalytic intramolecular hydroamination of an o-substituted alkynyl aniline, underscoring the advantage of using halide exchange reagents that produce soluble byproducts.