George G. Stanley

A bimetallic hydroformylation catalyst: high regioselectivity and reactivity through homobimetallic cooperativity.

The racemic and meso diastereomers of an electron-rich binucleating tetraphosphine ligand have been used to prepare homobimetallic rhodium norbornadiene complexes. The racemic bimetallic Rh complex is an excellent hydroformylation catalyst for 1-alkenes, giving both a high rate of reaction and high regioselectivity for linear aldehydes, whereas the meso complex is considerably slower and less selective. A mechanism involving bimetallic cooperativity between the two rhodium centers in the form of an intramolecular hydride transfer is proposed. Mono- and bimetallic model complexes in which the possibility for bimetallic cooperativity has been reduced or eliminated are very poor catalysts.

A partially closed-mode platinum dimer based on a binucleating hexaphosphine ligand system: Crystal structure of [Pt2Cl2(eHTp)2+][PF6−]2 (eHTP = (Et2PCH2CH2)2PCH2P(CH2CH2PEt2)2

Abstract The reaction of two equivalents of K2PtCl4 with the hexaphosphine ligand system (Et2PCH2CH2)2PCH2P(CH2CH2PEt2)2, EHTP, quantitatively yields the diamagnetic dimer species, Pt2Cl2(eHTP)2+, 3. The single-crystal X-ray structure of the PF6− salt of 3 reveals a distorted square-planar environment about the metal atoms with the EHTP ligand adopting a symmetrical bischelating/bridging, partially closed-mode coordination geometry with a PtPt distance of 4.6707(9) A.

Maghemite, silver, ceragenin conjugate particles for selective binding and contrast of bacteria.

New synthesis techniques are providing increasing control over many inorganic nanoparticle characteristics, facilitating the creation of new multifunctional theranostics. This report proposes the synthesis and testing of a combination nanoparticle comprised of a maghemite core for enhanced T2 MRI contrast diagnostics, a colloidal silver shell acting as an antimicrobial and therapeutic vehicle, and a ceragenin (CSA-124) surfactant providing microbial adhesion. A polyacrylic acid functionalized maghemite nanoparticle is synthesized by a high temperature organic phase reduction followed by thiol functionalization and gold cluster seeding. A silver shell is formed through AgNO3 reduction, and an oriented monolayer of the thiolated ceragenin, is bound through a self-assembly process. The process and products are characterized throughout synthesis through TEM, DLS, FT-IR, UV-Vis, ICP-OES, HPLC-ESI-TOF-MS, DC magnetization and susceptibility, X-ray diffraction, and in vitro MRI. Synthesized Diagnostic Antimicrobial Nanoparticles (DANs) were found to have a spherical morphology with a diameter of 32.47±1.83 nm, hydrodynamic diameter of 53.05±1.20 nm, maximum magnetic moment of 12 emu/g NP (54 emu/g Fe) with little variation due to temperature, and are predominantly paramagnetic. In vitro MRI studies show that DANs contrast well at concentrations as low as 9 ppm, and successfully adhere to Staphylococcus aureus. DAN MIC was determined to be approximately 12 ppm and 24 ppm against S. aureus and Escherichia coli respectively.

Visible-light-promoted selenofunctionalization of alkenes.

A visible-light-promoted method for the selenofunctionalization (and tellurofunctionalization) of alkenes has been developed. This method obviates the prepreparation of moisture-sensitive chalcogen electrophiles. The experimental setup is simple, and superior yields are obtained in the case of selenofunctionalization (up to 99%) while moderate to good yields are obtained in the case of tellurofunctionalization (53-75%). A variety of intra- and intermolecular processes and a short synthesis of the Amaryllidaceae alkaloid (±)-γ-lycorane are demonstrated with this method.

STRUCTURAL CHARACTERIZATION OF 1,2,4,5-TETRAPHENYLCYCLO-3,6-DICARBA-1,2,4,5-TETRAPHOSPHINE: A HIGHLY FOLDED CHAIR CONFORMATION

Abstract The title compound crystallized in the monoclinic space group P21/c, with the following unit cell parameters: a = 11.235(8), b = 8.473(2), c = 26.136(10) A, β = 102.07(5)°, V = 2432(3) A3, Z = 4.1657 unique data (Fo 2 > 3o(Fo 2)) were used to solve (direct methods) and refine the structure to give R = 0.126 and Rw = 0.118. The six-membered ring system is in a highly folded chair conformation with the phenyl group substituents on the phosphorus atoms oriented in the equatorial positions. The dihedral angles of the P-CH2-P plane with the P4 basal plane is a remarkable 101.8° (average). This dihedral angle is the closest to perpendicular ever observed for a monocyclic ring system.

Symmetric hydrogen bonding in dimethylammonium hydrogen diphenyldiphosphonate

In the title compound, C2H8N+.C12H11O5P2-, pairs of hydrogen diphenyldiphosphonate anions form dimers across a twofold axis, with two symmetric O...H...O hydrogen bonds [O...O = 2.406 (3) and 2.418 (3) A]. The 12-membered ring thus formed has crystallographic 2 and quasi-222 symmetry. Cations on either side of the ring form N-H...O hydrogen bonds to the four extraannular O atoms, with N...O distances of 2.765 (2) and 2.748 (3) A.

Bimetallic hydroformylation: a zwitterionic Rh–IRhI tetraphosphine ligand-based bimetallic complex exhibiting facile CO addition and phosphine ligand rearrangement equilibrium

The X-ray structure of an unsymmetrical tetraphosphine bridged zwitterionic Rh–IRhI dinuclear tetracarbonyl complex is reported along with the facile CO addition equilibrium to form an Rh0 tetraphosphine pentacarbonyl bimetallic species; both of these are poor hydroformylation catalysts due to the relatively high electron density on the rhodium centres, in marked contast to a dicationic bimetallic RhII complex based on the same tetraphosphine ligand that is a highly active and regioselective hydroformylation catalyst.

To bend or not to bend: electronic structural analysis of linear versus bent M-H-M interactions in dinickel bis(dialkylphosphino)methane complexes.

The M-H-M bonding in the dinuclear complexes Ni(2)(mu-H)(mu-P(2))(2)X(2) (P(2) = R(2)PCH(2)PR(2), R = iPr, Cy; X = Cl, Br) has been investigated. These dinickel A-frames were studied via density functional theory (DFT) calculations to analyze the factors that influence linear and bent M-H-M bonding. The DFT calculations indicate that the bent geometry is favored electronically, with ligand steric effects driving the formation of the linear M-H-M structures.

Refinement of lithium tetra­hydroxo­borate with low-temperature CCD data

Refinement of the title compound, Li B(OH)4, with CCD data at 120 K has led to a sevenfold increase in precision over the previously reported structure based on film data. The H atoms have been located and refined. Both Li and B are tetrahedrally coordinated. B—O distances are in the range 1.4644 (14)–1.4989 (13) A, while Li—O distances are in the range 1.931 (2)–2.022 (2) A.

The synthesis of heterobimetallic systems based on a hexatertiaryphosphine ligand system: cobalt-nickel and nickel-platinum complexes

Abstract Heterobimetallic complexes can be prepared in an extremely straightforward fashion by the use of the binucleating hexatertiaryphosphine ligand (Et 2