Desiree S. Grubisha

Electronic transport through metal-1,4-phenylene diisocyanide-metal junctions

Abstract We report measurements on through-bond electronic transport properties of 1,4-phenylene diisocyanide–metal junctions. Nanoscale metal–molecule–metal junctions with self-assembled 1,4-phenylene diisocyanide layers were analyzed with variable temperature conductance measurements to reveal the dominant electronic transport mechanisms. Non-Ohmic thermionic emission is the dominant process, with isocyanide–Pd showing the lowest thermionic barrier of 0.22 eV.

Molecular wires, switches, and memories.

Abstract: Design and measurements of molecular wires, switches, and memories offer an increased device capability with reduced elements. We report: Measurements on through‐bond electronic transport properties of nanoscale metal‐1,4‐phenylene diisocyanide‐metal junctions are reported, where nonohmic thermionic emission is the dominant process, with isocyanide‐Pd showing the lowest thermionic barrier of 0.22 eV; robust and large reversible switching behavior in an electronic device that utilizes molecules containing redox centers as the active component, exhibiting negative differential resistance (NDR) and large on‐off peak‐to‐valley ratio (PVR) are realized; erasable storage of higher conductivity states in these redox‐center‐containing molecular devices are observed; and a two‐terminal electronically programmable and erasable molecular memory cell with long bit retention time is demonstrated.

The synthesis of S-(+)-2,2-dimethylcyclopropane carboxylic acid: a precursor for cilastatin

Abstract S -(+)-2,2-Dimethylcyclopropane carboxylic acid, a precursor for cilastatin, was prepared from 2-methylpropene and chiral iron carbene in three steps. Asymmetric cyclopropanation reaction of 2-methylpropene with iron carbene complex having chirality at the carbene ligand, followed by exhaustive ozonolysis, produced S -(+)-2,2-dimethylcyclopropanecarboxylic acid of up to 92% ee. The absolute configuration of complexed chiral cyclopropane (−)- 8 was determined by X-ray crystallographic analysis.

Prospects for molecular-scale devices

The recent state-of-the-art of molecular-scale device systems utilizing self-assembled oligomers as the key fabrication strategy is discussed. A variety of devices have been demonstrated, including switches with inherent mechanisms significantly different from conventional solid state devices.

A structural study of sodium dithionite and its ephemeral dihydrate: A new conformation for the dithionite ion

Raman spectroscopy on solid anhydrous sodium dithionite reveals that it exists in at least two forms in the solid state. MAS23Na NMR spectra and X-ray powder diffraction patterns of the solids indicate that sodium ions are in different environments in each form of the material. The results suggest that the dithionite anion is conformationally different in each lattice. A single crystal X-ray diffraction study of the recrystallized form of anhydrous sodium dithionite reveals an anion with C2 geometry and a 16° O-S-S-O torsional angle; nearly eclipsed. (Crystal Data for recrystallized Na2S2O4 area=6.539(1) Å,b=6.552(1) Å,c=6.578(1) Å,V=240.0(1) Å3,β=121.61(1)°, space group=P2/c,Z=2). Raman spectra of sodium dithionite dihydrate reveal that the dithionite ion is in a different conformation than in either of the anhydrous materials. A single crystal X-ray diffraction study of Na2S2O4·2H2O reveals a dithionite anion with a substantially shorter S-S bond length than in the anhydrous structure and an O-S-S-O torsional angle of 56°; approximately gauche. (Crystal Data for Na2S2O4·2H2O area=8.134(1) Å,b=5.756(2) Å,c=14.528(5) Å,V=653.3(3) Å3,β=106.20(2)°, space group=P21/n,Z=4). The structure of the dithionite anion is found to depend critically upon the nature of its external environment.

Crystal and molecular structure of benzophenone azine: evidence for an Fe(II) carbene intermediate

Benzophenone azine crystallizes in the monoclinic space groupA2/a (No. 15) witha=16.303(3) Å,b=5.4864(2) Å,c=21.973(5) Å, β=85.52(2)°,V=1959.4(8) Å3, andDcalc=1.22 g cm−3 forZ=4. The structure was solved by direct methods and refined againstF to a finalR value of 0.047. The unit cell contains four molecules of the title compound; the asymmetric unit consists of half a molecule. Despite the high crystallographic symmetry, the two halves of the molecule arenot related by a center of symmetry; instead, the molecule adopts C2 symmetry; the molecular C2 axis is coincident with the crystallographic twofold axis. The formation of benzophenone azine from the reaction of the iron-containing Lewis acid complex [(η5-C5H5)Fe(CO)2(THF)]+ [BF4]− and diphenyldiazomethane provides strong evidence for an Fe(II) carbene intermediate.

The structure of trans-1,4-diisocyanocyclohexane in solution, in the solid state, and as a ligand bridging bulky tungsten(II) complexes

Abstract The conformational structures of the bridging ligand trans -1,4-diisocyanocyclohexane were determined in solution, as a solid, and as a ligand bridging bulky seven-coordinate tungsten(II) complexes. In solution CNC 6 H 10 NC exists as an equilibrium mixture of diaxial and diequatorial conformers, with the diequatorial conformer preferred in a 2 : 1 ratio. Infrared data indicate that the bulk solid does not consist of the diequatorial conformer, and a single-crystal study verifies that the diaxial conformer is preferred in the solid state. The crystal data found for CNC 6 H 10 NC are: space group P 2 1 /n, Z = 2, a = 5.996(1) A, b = 7.203(2) A, c = 8.972(3) A, β = 96.89(2)°, and V = 384.7(2) A 3 . 13 C NMR bandshape analysis provides a low activation barrier (40.7(4) kJ mol −1 ) in CH 2 Cl 2 solution for diaxial—diequatorial conversion. In spite of the accessibility of both conformers in solution, the ligand unexpectedly adopts the diaxial conformation in the bimetallic complex (Br 2 (PEt 3 ) 2 (CO) 2 W) 2 CNC 6 H 10 NC. The crystal data found for (Br 2 (PEt 3 ) 2 (CO) 2 W) 2 CNC 6 H 10 NC are: space group Pca 2 1 , Z = 4, a = 17.162(5) A, b = 16.226(6) A, c = 18.233(3) A, and V = 5077.3(25) A 3 .

Pictet-spengler reactions in aprotic media. The total synthesis of (±) suaveoline

Abstract The first total synthesis of the indole alkaloid (±)-suaveoline 1 (a macroline-related base and a member of the sarpagine/ajmaline class of alkaloids) was completed in a stereocontrolled fashion. The serial synthesis employed three intramolecular reactions, the Pictet-Spengler cyclization ( 11 → 20 ), the Dieckmann condensation ( 21 → 22 ) and the orthoester Claisen rearrangement ( 25 → 30 ), all of which occurred with high stereoselectivity. Construction of the unique 3,4,5-trisubstituted pyridine ring ( E ) of 1 was executed by addition of hydroxylamine hydrochloride to an ethanolic solution of the corresponding 1,5-daildehyde 36 which was followed by heating. The related base (±)-N b -methylsuaveoline 38 was prepared from 37 via catalytic devenzylation (Pd/C, H 2 ) in the presence of formic acid (78% yield).

Crystal and molecular structure of trans-(tricarbonyl)bis(trans-2,2,3,4,4-pentamethyl-1-phenylphosphetane)iron

The title compound crystallizes in the monoclinic space groupP21/a witha=13.092(2) Å,b=15.853(2) Å,c=15.406(3) Å,β=103.00(1)°,V=3116(1) Å3, andDcalc=1.237 g cm−3 forZ=4. The structure was solved by direct methods, and refined to a finalR value of 0.057. The phosphetane ligands adopt a nonlinear trans relationship. The four-membered rings are non-planar and have different flap angles of 6.1 and 20.3°. Virtual coupling is evident in the13C NMR spectrum of the title compound. Comparison of the13C NMR spectral data of this molecule with the parent phosphine ligand, the ligand oxide, and the mono-phosphine iron complex is provided.