Bruce C. Noll

A Tetrameric Cage with D2h Symmetry through Alkyne Metathesis

Shape-persistent covalent organic polyhedrons (COPs) with ethynylene linkers are usually prepared through kinetically controlled cross-coupling reactions. The high-yielding synthesis of ethynylene-linked rigid tetrameric cages via one-step alkyne metathesis from readily accessible triyne precursors is presented. The tetrameric cage contains two macrocyclic panels and exhibits D2h symmetry. The assembly of such a COP is a thermodynamically controlled process, which involves the initial formation of macrocycles as key intermediates followed by the connection of two macrocycles with ethynylene linkages. With a large internal cavity, the cage exhibits a high binding selectivity toward C70 (K = 3.9×10(3) L mol(-1)) over C60 (no noticeable binding).

Iron(I)-carbonyl clusters tethered to (trifluoromethyl)thiophenolates

Two diironhexacarbonyl clusters containing (trifluoromethyl)thiophenolates, as models for the active site of [Fe–Fe] hydrogenase enzyme, have been prepared and characterized. The crystal and electronic structures of the complexes have been probed by X-ray crystallography and spectroscopic methods. Cyclic voltammetric studies in the presence of acetic acid show that both compounds catalyze the electrochemical reduction of acetic acid to produce hydrogen with favorable overpotentials.

2-(Thio-phen-2-yl)-1-(thio-phen-2-ylmeth-yl)-1H-benzimidazole.

In the title compound, C16H12N2S2, the thiophene groups are rotationally disordered over two sets of sites, by approximately 180°, with occupancy ratios of 0.916 (2):0.084 (2) and 0.903 (2):0.097 (2). The major components of the thiophene and methylene substituted thiophene rings are canted by 24.06 (12) and 85.07 (10)°, respectively, from the benzimidazole ring system plane and the dihedral angle between the major component thiophene ring planes is 84.90 (14)°. In the crystal, there is a weak C—H⋯N hydrogen bond which links molecules into chains.

Synthesis of chiral disulfides: potential reagents for enantioselective sulfurization

Synthesis of chiral phosphorothioates for use as antisense oligonucleotides might benefit from the use of chiral disulfides. This paper reports the synthesis of chiral analogs of phenylacetyl disulfide and of 5-methyl-3H-1,2,4-dithiazol-3-one from the same set of 2-arylalkanoic acids. The X-ray crystal structures of the disulfides derived from (R) and [S]-2-phenylpropanoic acid establish the stereochemistry and the helicity of these materials, and density functional theory calculations suggest that the high specific rotations can be due to preferred retention of this helicity in solution. Chiral HPLC showed that the final products were formed with enantiomeric purities from 86.1% to>99.9%.

C(sp3)−H Oxidative Addition and Transfer Hydrogenation Chemistry of a Titanium(II) Synthon: Mimicry of Late‐Metal Type Reactivity

Two-electron reduction of the TiIV compound (ket guan)(ImDipp N)Ti(OTf)2 (3) gives the arene-masked complex (ket guan)(η6 -ImDipp N)Ti (1) in excellent yield. Upon standing in solution, 1 converts to a TiIV metallacycle (4) through dehydrogenation of a pendant isopropyl group. Spectroscopic evidence shows this transformation initially proceeds via the oxidative addition of a C(sp3 )-H bond and can be reversed upon exposure of 4 to H2 . Interestingly, treatment of 1 with cyclohexene gives cyclohexane and 4 via a titanium-mediated transfer hydrogenation reaction, a process that can be extended to catalytically hydrogenate other unsaturated hydrocarbons under mild conditions. These results, rare for the early-metals, suggest 1 possesses chemical characteristics reminiscent of noble, late-metals.

Incommensurate density modulation in a Na-rich plagioclase feldspar: Z-contrast imaging and single-crystal X-ray diffraction study

Plagioclase feldspars are the most abundant mineral in the Earths crust. Intermediate plagioclase feldspars commonly display incommensurately modulated or aperiodic structures. Z-contrast images show both Ca-Na ordering and density modulation. The local structure of lamellae domains has I1-like symmetry. The neighboring lamellae domains are in an inversion twinning relationship. With a state-of-the-art X-ray diffraction unit, second-order satellite reflections (f-reflections) are observed for the first time in andesine (An45), a Na-rich e-plagioclase. The f-reflections indicate a structure with a density modulation which is close to a Ca-rich e-plagioclase. The similarity between this e-andesine structure and previously solved e-labradorite structure is confirmed. Refinement of the structure shows density modulation of ∼ 7 mol % in compositional variation of the anorthite (An) component. The results from Z-contrast imaging and low-temperature single X-ray diffraction (XRD) provide a structure consistent with density modulation. The discovery of f-reflections in Na-rich e-plagioclase extends the composition range of e1 structure with density modulation to as low as at least An45, which is the lower end of the composition range of Bøggild intergrowth. The new result supports the loop-shaped solvus for Bøggild intergrowth, below which is a homogenous stable area for e1 structure in the phase diagram. The phase transition between e2 structure without density modulation and e1 structure with density modulation should happen at low temperature. There is a change in modulation period accompanying the phase transition, as well as higher occupancy of Al in the T1o site. The andesine with density modulation also indicates extremely slow cooling of its host rock.

Crystal structure of abelsonite, the only known crystalline geoporphyrin

Abstract The crystal structure of the unique nickel porphyrin mineral abelsonite, NiC31H32N4, has been solved using direct methods with 2195 independent reflections to a final R1 = 0.0406. Abelsonite crystallizes in the triclinic space group P 1¯

Bis(1,4,7-trithia-cyclo-nona-ne)nickel(II) bis-(tetra-fluorido-borate) nitro-methane disolvate.

\bar {1}

Implications of bond disorder in a S = 1 kagome lattice

, with Z = 1 and unit-cell parameters a = 8.4416(5) Å, b = 10.8919(7) Å, c = 7.2749(4) Å, α = 90.465(2)°, β = 113.158(2)°, and γ = 78.080(2)° at the measurement condition of 100 K, in very good agreement with previous unit-cell parameters reported from powder diffraction. The structure consists of nearly planar, covalently bonded porphyrin molecules stacked approximately parallel to (1 1¯

Synthesis and crystal structure of [2,7,12-trimethyl-3,7,11,17-tetra­aza­bicyclo­[11.3.1]hepta­deca-1(17),13,15-triene-κ4N]copper(II) bis­(perchlorate)

\bar {1}