Generation and reactivity of rhodium(IV) complexes in aqueous solutions

At pH = 1 and 25 degrees C, the Fenton-like reactions of Fe(aq)(2+) with hydroperoxorhodium complexes LRh(III)OOH(2+) (L = (H(2)O)(NH(3))(4), k = 30 M(-1) s(-1), and L = L(2) = (H(2)O)(meso-Me(6)-[14]aneN(4)), k = 31 M(-1) s(-1)) generate short-lived, reactive intermediates, believed to be the rhodium(IV) species LRh(IV)O(2+). In the rapid follow-up steps, these transients oxidize Fe(aq)(2+), and the overall reaction has the standard 2:1 [Fe(aq)(2+)]/[LRhOOH(2+)] stoichiometry. Added substrates, such as alcohols, aldehydes, and (NH(3))(4)(H(2)O)RhH(2+), compete with Fe(aq)(2+) for LRh(IV)O(2+), causing the stoichiometry to change to <2:1. Such competition data were used to determine relative reactivities of (NH(3))(4)RhO(2+) toward CH(3)OH (1), CD(3)OH (0.2), C(2)H(5)OH (2.7), 2-C(3)H(7)OH (3.4), 2-C(3)D(7)OH (1.0), CH(2)O (12.5), C(2)H(5)CHO (45), and (NH(3))(4)RhH(2+) (125). The kinetics and products suggest hydrogen atom abstraction for (NH(3))(4)RhO(2+)/alcohol reactions. A short chain reaction observed with C(2)H(5)CHO is consistent with both hydrogen atom and hydride transfer. The rate constant for the reaction between Tl(aq)(III) and L(2)Rh(2+) is 2.25 x 10(5) M(-1) s(-1).     

Electron correlation effects on the shape of the Kohn–Sham molecular orbital

Even systems in which strong electron correlation effects are present, such as the large near-degeneracy correlation in a dissociating electron pair bond exemplified by stretched H₂, are represented in the Kohn–Sham (KS) model of non-interacting electrons by a determinantal wavefunction built from the KS molecular orbitals. As a contribution to the discussion on the status and meaning of the KS orbitals we investigate, for the prototype system of H₂ at large bond distance, and also for a one-dimensional molecular model, how the electron correlation effects show up in the shape of the KS σ _g orbital. KS orbitals φ^HL and φ^FCI obtained from the correlated Heitler-London and full configuration interaction wavefunctions are compared to the orbital φ^LCAO, the traditional linear combination of atomic orbitals (LCAO) form of the (approximate) Hartree-Fock orbital. Electron correlation manifests itself in an essentially non-LCAO structure of the KS orbitals φ^HL and φ^FCI around the bond midpoint, which shows up particularly clearly in the Laplacian of the KS orbital. There are corresponding features in the kinetic energy density t _s of the KS system (a well around the bond midpoint) and in the one-electron KS potential v _s (a peak). The KS features are lacking in the Hartree-Fock orbital, in a minimal LCAO approximation as well as in the exact one. Received: 11 December 1996 / Accepted: 10 January 1997     

2,2′-Isopropylidenebis[(4S,5R)-4,5-di(2-naphthyl)-2-oxazoline] ligand for asymmetric cyclization-carbonylation of meso-2-alkyl-2-propargylcyclohexane-1,3-diols

The oxidative cyclization-carbonylation of meso-2-alkyl-2-propargylcyclohexane-1,3-diols mediated by Pd(II) with chiral bisoxazoline (box ligand) afforded bicyclic-β-alkoxyacrylates. Based on a ligand screening, 2,2′-isopropylidenebis[(4S,5R)-4,5-di(2-naphthyl)-2-oxazoline] ligand has been developed. The products with a chiral quaternary carbon were obtained in 71-100% yields with 85-95% ee.     

A revised quantum chemistry-based potential for poly(ethylene oxide) and its oligomers in aqueous solution

We have conducted a high-level quantum chemistry study of the interactions of 1,2-dimethoxyethane (DME) with water for complexes representing both hydrophilic and hydrophobic hydration. It was found that our previous quantum chemistry-based force field for poly(ethylene oxide) (PEO) and its oligomers in aqueous solution did a poor job in describing the hydrophobic binding of water to the ether, consistent with our recent calculations of the excess free energy and entropy of hydration of DME. Our original force field was revised to more accurately reproduce the interaction of water with the carboneous portions of DME. Molecular dynamics simulations of aqueous DME solutions using the revised quantum chemistry-based potential yielded good agreement with experiment for excess free energy, enthalpy, and volume as well as excess solution viscosity and the self-diffusion of water. Comparison with our original potential revealed that the relatively hydrophobic ether-water interactions in the new potential strongly reduced the favorable excess free energy and enthalpy but have relatively little influence on the excess entropy for dilute DME solutions. Other properties of DME and PEO solutions including conformational populations and dynamics, solution viscosity, hydrogen bonding, water translational and rotational diffusion and neutron structure factor as a function of solution composition were found to be largely unchanged from those obtained using the original potential.     

Two isomeric phosphacarboranes 2,1- and 6,1-PCB(8)H(9), the first representatives of the 10-vertex closo phosphacarborane Series

The reaction between arachno-4-CB(8)H(14) and PCl(3) in the presence of PS (PS = proton sponge = 1,8-dimethylamino naphthalene) (dichloromethane, rt, 24 h) produced the neutral phosphacarborane closo-2,1-PCB(8)H(9) (35% yield), while a similar reaction of nido-1-CB(8)H(12) gave the isomeric compound closo-6,1-PCB(8)H(9) (27% yield). The structures of both compounds were derived on the basis of the combined ab initio/GIAO/NMR ((1)H, (11)B, (13)C) approach. The optimized structures at a correlated level of theory (MP2) with 6-31G* basis set were used as a basis for calculations of the (11)B and (13)C chemical shifts at GIAO-SCF/II and GIAO-MP2/II, the latter showing excellent agreement with experimental data.     

Luminescent properties of PP and LDPE films and rods doped with the Eu(III)‐La(III) complex

The work is devoted to luminescent properties of trivalent lanthanide complexes dispersed in thermoplastic host matrices. Polyethylene films and polypropylene‐rods, both doped with these complexes, were manufactured using an extrusion technique. Two kinds of dopants were used: Eu(III)‐thenoyltrifluoroacetone‐1,10‐phenanthroline complex (1) and Eu(III)‐La(III)‐1,10‐phenanthroline complex (2). Absorption, excitation, emission spectra and lifetime of luminescence were studied. The impact of the polymer matrix on the emission spectra was investigated. Emission spectra of the films were studied at room and helium temperatures. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) surface mapping showed that in the Eu(III)‐La(III) complex europium forms islands (clusters) with a dimension of 1 µm, whereas lanthanum was dispersed more uniformly in the polymer matrix. Dependence of emission intensity on the excitation was determined. Copyright © 2006 John Wiley & Sons, Ltd.     

1‐Oxa‐nido‐dodecaborate [OB11H12]− from the Controlled Oxidation of the closo‐Borates [B11H11]2− and [B12H12]2−

The closo‐dodecaborate [B₁₂H₁₂]^2? is degraded at room temperature by oxygen in an acidic aqueous solution in the course of several weeks to give B(OH)₃. The degradation is induced by Ag²⁺ ions, generated from Ag⁺ by the action of H₂S₂O₈. Oxa‐nido‐dodecaborate(1?) is an intermediate anion, that can be separated from the reaction mixture as [NBzlEt₃][OB₁₁H₁₂] after five days in a yield of 18 %. The action of FeCl₃ on the closo‐undecaborate [B₁₁H₁₁]^2? in an aqueous solution gives either [B₂₂H₂₂]^2? (by fusion) or nido‐B₁₁H₁₃(OH)^? (by protonation and hydration), depending on the concentration of FeCl₃. In acetonitrile, however, [B₁₁H₁₁]^2? is transformed into [OB₁₁H₁₂]^? by Fe³⁺ and oxygen. The radical anions [B₁₂H₁₂] ^{˙ ?} and [B₁₁H₁₁] ^{˙ ?} are assumed to be the primary products of the oxidation with the one‐electron oxidants Ag²⁺ and Fe³⁺, respectively. These radical anions are subsequently transformed into [OB₁₁H₁₂]^? by oxygen. The crystal structure analysis shows that the structure of [OB₁₁H₁₂]^? is derived from the hypothetical closo‐oxaborane OB₁₂H₁₂ by removal of the B3 vertex, leaving a non‐planar pentagonal aperture with a three‐coordinate O vertex, as predicted by NMR spectra and theory.     

Complexing processes in M(II)-dithiomalonamide-diacetyl triple systems (M= Ni,Cu) in ethanol solution and in a metal(II)hexacyanoferrate(II) gelatin-immobilized matrix materials

The complexing processes in the M ^II -dithiomalonamide-diacetyl triple system (M=Ni, Cu) occuring in the nickel(II)- and copper(II)hexacyanoferrate(II) gelatin-immobilized matrix in contact with aqueous alkaline solutions (pH~12) containing dithiomalonamide and diacetyl at room temperature, and between MCl₂, dithiomalonamide and diacetyl in EtOH solutions upon heating to$80°C, have been studied. In the Ni ^II -dithiomalonamide-diacetyl system, template synthesis occurs in EtOH solution but does not occur in the gelatin-immobilized matrix, whereas in the Cu ^II -dithiomalonamide-diacetyl system, template synthesis occurs in the gelatin-immobilized matrix but not in EtOH solution. Dithiomalonamide and diacetyl are the ligand synthons in the processes indicated.     

Deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls

Construction of C–C bonds at the α-carbon is a challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation of unselective, strongly basic and nucleophilic reagents permits carrying out the reaction in the presence of electrophiles that intercept the intermediate boron enolates, resulting in two new α-C–C bonds in a tricomponent process.

α-Branched carboxylic acids and other carbonyls are readily accessed by a metal- and base-free deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls via boron enolates, resulting in a tricomponent coupling with unconventional electrophiles.     

Liquid crystal effects on bacterial viability

The primary objective of this research was to test the hypothesis that lyotropic chromonic liquid crystals (neutral grey, red 14, blue 27, cromolyn) are not toxic to bacteria as compared with surfactant-based lyotropic (CPCl and CsPFO) or thermotropic (5CB and E7) liquid crystals. Biocompatibility of most liquid crystals is currently unknown and is required for the development of systems interfacing liquid crystals and biological systems. Potential liquid crystal toxicity was evaluated by two methods. The first examined bacterial survival measured by bacterial growth over 24 hours, after exposure to various liquid crystals. The second toxicity method evaluated liquid crystal effects on bacterial membrane permeability using two fluorescent dyes. Three different types of bacteria were evaluated to assess bacterial structure differences with respect to liquid crystal toxicity. The results of this study indicate that lyotropic chromonic liquid crystals are not toxic to bacteria, whereas thermotropic and surfactant-based lyotropic liquid crystals are toxic to one or more forms of bacteria. We conclude that lyotropic chromonic liquid crystals may be the preferred material in designing liquid crystal-based systems that interact with biological systems, especially in the use of liquid crystal-based biosensors.