David M. Eichhorn

Structure, NMR and other physical and photophysical properties of ruthenium(II) complexes containing the 3,3′-dicarboxyl-2,2′-bipyridine ligand

Abstract A series of compounds of the type [(bpy) 2 Ru(3,3′-XX-2,2′-bpy)] 2+ or [(dmb) 2 Ru(3,3′-XX-2,2′-bpy)] 2+ , where X is CH 2 OH, COOH, COOCH 3 , COOC 2 H 5 , and COOCH 2 C 6 H 5 and bpy and dmb are 2,2′-bipyridine and 4,4′-dimethyl-2,2′-bipyridine, respectively, have been synthesized. [Ru(bpy) 2 ((COOCH 3 ) 2 bpy)](PF 6 ) 2 ·2CH 3 CN crystallized in the monoclinic space group P 2 1 / c with a =15.347 (3), b =22.767 (4), c =12.971 (3) A, and Z =4. 1 H-NMR spectra were assigned. The proton on the carbon atom neighboring the nitrogen coordination site shifts upfield upon coordination to ruthenium(II). Electronic absorptions occur over the visible region from 550 to 400 nm, which are attributed to metal-to-ligand charge transfer and in the UV region from 250 to 350 nm, which are associated with intraligand processes. The absorbance in the visible region of the spectrum displays two components, Ru(dπ)→π*(bpy) and Ru(dπ)→π*((COOR) 2 bpy) for R=CH 3 , C 2 H 5 and CH 2 C 6 H 5 , in the other cases the Ru(dπ)→π* transitions to the three bipyridine ligands overlap. Reduction potentials attributed to the Ru(III/II) couple range from 1.22 V for the CH 2 OH derivative to 1.40 V versus SSCE for the COOC 2 H 5 derivative. Reductions attributed to the first reduction of the coordinated (3,3′-XX-2,2′-bpy) ligand occur over the range −0.88 to −1.36 V versus SSCE. Emission maxima at room temperature in acetonitrile range from 614 nm for the CH 2 OH derivative to 711 nm for the ester derivatives; their emission lifetimes at room temperature in acetonitrile vary from 940 to 258 ns, respectively.

Refinement of the nickel site structure in Desulfovibrio gigas hydrogenase using range-extended EXAFS spectroscopy

We have reexamined the Ni EXAFS of oxidized, inactive (as-isolated) and H(2) reduced Desulfovibrio gigas hydrogenase. Better spatial resolution was achieved by analyzing the data over a 50% wider k-range than was previously available. A lower k(min) was obtained using the FEFF code for phase shifts and amplitudes. A higher k(max) was obtained by removing an interfering Cu signal from the raw spectra using multiple energy fluorescence detection. The larger k-range allowed us to better resolve the Ni-S bond lengths and to define more accurately the Ni-O and Ni-Fe bond lengths. We find that as-isolated, hydrogenase has two Ni-S bonds at approximately 2.2 A, but also 1-2 Ni-S bonds in the 2.35+/-0.05 A range. A Ni-O interaction is evident at 1.91 A. The as-isolated Ni-Fe distance cannot be unambiguously determined. Upon H(2) reduction, two short Ni-S bonds persist at approximately 2.2 A, but the remaining Ni-S bonds lengthen to 2.47+/-0.05 A. Good simulations are obtained with a Ni-Fe distance at 2.52 A, in agreement with crystal structures of the reduced enzyme. Although not evident in the crystal structures, an improvement in the fit is obtained by inclusion of one Ni-O interaction at 2.03 A. Implications of these distances for the spin-state of H(2) reduced H(2)ase are discussed.

Design, synthesis and characterization of novel 1,2-benzisothiazol-3(2H)-one and 1,3,4-oxadiazole hybrid derivatives: potent inhibitors of Dengue and West Nile virus NS2B/NS3 proteases.

1,2-Benzisothiazol-3(2H)-ones and 1,3,4-oxadiazoles individually have recently attracted considerable interest in drug discovery, including as antibacterial and antifungal agents. In this study, a series of functionalized 1,2-benzisothiazol-3(2H)-one-1,3,4-oxadiazole hybrid derivatives were synthesized and subsequently screened against Dengue and West Nile virus proteases. Ten out of twenty-four compounds showed greater than 50% inhibition against DENV2 and WNV proteases ([I] = 10 μM). The IC(50) values of compound 7n against DENV2 and WNV NS2B/NS3 were found to be 3.75 ± 0.06 and 4.22 ± 0.07 μM, respectively. The kinetics data support a competitive mode of inhibition by compound 7n. Molecular modeling studies were performed to delineate the putative binding mode of this series of compounds. This study reveals that the hybrid series arising from the linking of the two scaffolds provides a suitable platform for conducting a hit-to-lead optimization campaign via iterative structure-activity relationship studies, in vitro screening and X-ray crystallography.

[60]Fullerene and TCNQ donor–acceptor crystals of octakis(dimethylamino) porphyrazine

Reaction of octakis(dimethylamino) porphyrazine 1 with [60]fullerene gives a crystalline 2:1 charge-transfer (CT) complex as a three-dimensional network of chains; in contrast, reaction of 1 with tetracyanoquinodimethane (TCNQ) gives a crystalline 1:1 charge transfer salt as one-dimensional integrated stacks.

Cyanoscorpionates: synthesis and crystallographic characterization of one-dimensional Cu(I) coordination polymers

A new cyanoscorpionate ligand, hydrotris(3- t-butyl-4-cyanopyrazolyl)borate (Tp ( t-Bu,4CN )) is reported. Both Tp ( t-Bu,4CN ) and hydrotris(4-cyano-3-phenylpyrazolyl)borate (Tp (Ph,4CN)) form one-dimensional coordination polymers with Cu(I). The polymeric chains align to form channels which, in the case of Tp ( t-Bu,4CN ), can encapsulate solvent molecules, as evidenced by the characterization of one such polymer with encapsulated acetonitrile molecules.

Crystal structure and physical properties of a ruthenium(II) bipyridine dimethylsulfoxide complex

The complex [Ru(bpy)2(DMSO)C1]PF6, where bpy is 2,2′-bipyridine and DMSO is dimethylsulfoxide, crystallizes in the triclinic space group P1¯ (#2) with a = 8.873 (2), b = 12.805 (4), c = 12.864 (4) Å, α = 97.76(3), β = 106.45(2), γ = 107.88(2); Z = 2, and dcalc = 1.75 mg/m3. The coordination geometry is that of a distorted octahedron with a cis −RuN4SCl arrangement of coordinating atoms. The four Ru—N distances to the bpy ligands are 2.082(5), 2.092(4), 2.044(4), and 2.078(5) Å. The Ru—Cl distance is 2.421(2) Å and the Ru—S distance to DMSO is 2.260(1) Å. The Ru—N bond distance trans to Cl is the shortest; the Ru—N bond distance trans to S is the longest. The complex is oxidized and reduced reversibly at 1.13 and −1.37 V vs. SSCE, respectively. It displays electronic absorptions at 515, 480 (1.5 × 104), 342 (1.5 × 104), 292 (1.2 × 105), and 240 nm (6.2 × 104) and has a broad emission band centered at 607 nm at 77 K in a 4:1 ethanol/methanol glass. The emission lifetime at room temperature is less than the pulse width of the laser, τ < 20 ns.

Formation of an ethylene-bridged bis(benzisothiazole) dication by oxidative decomplexation of Ni(tsalen) with FeCl3

Abstract Treatment of Ni(tsalen), where H2tsalen = bis(thiosalicylidene)imine with FeCl3 results in the isolation of a crystalline compound with the composition [BBITE2+][Ni(tsalen)]4[FeCl4−]2 (I), where BBITE=1,2-bis(1,2-benzisothiazol-2-yl)ethane. The production of the BBITE2+ cation represents a 4-electron oxidation of the tsalen2− ligand, even though FeCl3 is not a strong enough oxidant to promote any outer-sphere oxidation of the Ni(tsalen) complex. The crystal structure of I shows a series of channels which are maintained by non-covalent interactions between the [Ni(tsalen)] and BBITE2+ molecules.

New Synthetic Techniques for Incorporation of Thiolate Donation in Transition Metal Complexes

A new method for the synthesis of metal complexes containing mixed nitrogen/sulfur coordination spheres is discussed. The use of 2,2′-dithiodibenzaldehyde as the source of the sulfur donors obviates the need for protection of the thiolate moiety. The reaction involves a concerted Schiff-base condensation and disulfide bond reduction. Mononuclear and dinuclear complexes of Ni(II), Cu(II), Fe(III), and Co(III) have been prepared by this method, including the first mononuclear Ni(II) complex of a non-porphyrinic tetradentate N3S ligand.

2-Fluoro-l-histidine.

The title compound, C6H8FN3O2, an analog of histidine, shows a reduced side-chain pKa (ca 1). The title structure exhibits a shortening of the bond between the proximal ring N atom and the F-substituted ring C atom, indicating an increase in π-bond character due to an inductive effect of fluorine.

Synthesis and characterization of tetrahedrally and octahedrally coordinated mixed-valence Co(II)/Co(III) complex with thiosemicarbazone-based ligand

Synthesis, characterization, and X-ray crystal structure for a mixed-valence binuclear Co(II)/Co(III) complex with the dianionic dithiolate form of a pentadentate ligand 2,6-diacetylpyridinebis(thiosemicarbazone) are reported. A new synthetic methodology has been employed replacing usual cobalt(II) salts by [Co(NH3)5Cl]Cl2 as a precursor. The coordination geometry of cobalt(II), CoN2S2, was found to be distorted tetrahedral, whereas the cobalt(III) coordination sphere, CoN4S2, is slightly distorted octahedral. The magnetic behavior and molar conductivity of the complex are in agreement with the mixed-valence state.