Wesley Sattler

Zinc Catalysts for On-Demand Hydrogen Generation and Carbon Dioxide Functionalization

[Tris(2-pyridylthio)methyl]zinc hydride, [κ(3)-Tptm]ZnH, is a multifunctional catalyst that is capable of achieving (i) rapid release of hydrogen by protolytic cleavage of silanes with either water or methanol and (ii) hydrosilylation of aldehydes, ketones, and carbon dioxide. For example, [κ(3)-Tptm]ZnH catalyzes the release of 3 equivalents of H(2) by methanolysis of phenylsilane, with a turnover number of 10(5) and a turnover frequency surpassing 10(6) h(-1) for the first 2 equivalents. Furthermore, [κ(3)-Tptm]ZnH also catalyzes the formation of triethoxysilyl formate by hydrosilylation of carbon dioxide with triethoxysilane. Triethoxysilyl formate may be converted into ethyl formate and N,N-dimethylformamide, thereby providing a means for utilizing carbon dioxide as a C(1) feedstock for the synthesis of useful chemicals.

Synthesis, Structure, and Reactivity of a Mononuclear Organozinc Hydride Complex: Facile Insertion of CO2 into a Zn–H Bond and CO2-Promoted Displacement of Siloxide Ligands

Tris(2-pyridylthio)methane, [Tptm]H, has been employed to synthesize the mononuclear alkyl zinc hydride complex, [κ(3)-Tptm]ZnH, which has been structurally characterized by X-ray diffraction. [κ(3)-Tptm]ZnH provides access to a variety of other [Tptm]ZnX derivatives. For example, [κ(3)-Tptm]ZnH reacts with (i) R(3)SiOH (R = Me, Ph) to give [κ(4)-Tptm]ZnOSiR(3), (ii) Me(3)SiX (X = Cl, Br, I) to give [κ(4)-Tptm]ZnX, and (iii) CO(2) to give the formate complex, [κ(4)-Tptm]ZnO(2)CH. The bis(trimethylsilyl)amide complex [κ(3)-Tptm]ZnN(SiMe(3))(2) also reacts with CO(2), but the product obtained is the isocyanate complex, [κ(4)-Tptm]ZnNCO. The formation of [κ(4)-Tptm]ZnNCO is proposed to involve initial insertion of CO(2) into the Zn-N(SiMe(3))(2) bond, followed by migration of a trimethylsilyl group from nitrogen to oxygen to generate [κ(4)-Tptm]ZnOSiMe(3) and Me(3)SiNCO, which subsequently undergo CO(2)-promoted metathesis to give [κ(4)-Tptm]ZnNCO and (Me(3)SiO)(2)CO.

Reticulated Heterojunctions for Photovoltaic Devices

An organic semiconductor device is formed by the self-assembly on a transparent electrode surface. The donor (see picture; dibenzotetrathienocoronene, yellow layer) deposits as supramolecular cables, and the acceptor (C60, orange) subsequently infiltrates this network. This network provides a donor–acceptor interface that is interwoven at the nanoscale. When incorporated into a solar cell, the active layer provides large increases in power conversion efficiencies.

Shape-shifting in contorted dibenzotetrathienocoronenes

We detail a general method for the synthesis of dibenzotetrathienocoronenes and elucidate their solid state structures in crystals and co-crystals. The contorted dibenzotetrathienocoronene (c-DBTTC) is a tetrathiophene-fused version of the previously studied contorted hexabenzocoronenes (c-HBC). The synthesis detailed here is simple and provides easy access to this important class of materials. We have found that these materials display molecular flexibility and tunable supramolecular self-assembly properties in the solid state by shifting molecular conformations between two different conformations. Depending on the conditions under which a c-DBTTC-containing material crystallizes, the c-DBTTC adopts either the “up-down” or the “butterfly” conformation. When grown from the vapor phase, crystals of the unsubstituted c-DBTTC show the molecule only in the up-down conformation, and it packs into dense crystals containing columnar arrays with close intracolumnar packing. The packing is controlled by the inherent molecular corrugation of the three-dimensional core and sulfur–sulfur interactions. When grown as co-crystals with electron acceptors from solution, the butyl-substituted c-DBTTC either adopts the butterfly conformation when the electron acceptor is small enough to be completely enveloped (TCNQ) or the up-down conformation when the electron acceptor is relatively large (C60). When grown from organic solvent crystals of the butyl-substituted c-DBTTC contain molecules of the solvent as the only guest, and we observe both conformations of the c-DBTTC. Controlling the supramolecular structure is the key to developing these materials for electronic applications.

A General Strategy for the Stereocontrolled Preparation of Diverse 8- and 9-Membered Laurencia-Type Bromoethers

A unique procedure to effect a ring-expanding bromoetherification process is described, wherein tetrahydrofurans and tetrahydropyrans are smoothly transformed into 8- and 9-membered bromoethers in a regio- and stereocontrolled manner through the use of BDSB (bromodiethylsulfonium bromopentachloroantimonate). These products resemble the cores of the Laurencia C15 acetogenins. In light of the generality and effectiveness of the approach, this work provides a unique strategy for their laboratory preparation and may implicate a possible biosynthesis pathway.

Generation of Powerful Tungsten Reductants by Visible Light Excitation

The homoleptic arylisocyanide tungsten complexes, W(CNXy)6 and W(CNIph)6 (Xy = 2,6-dimethylphenyl, Iph = 2,6-diisopropylphenyl), display intense metal to ligand charge transfer (MLCT) absorptions in the visible region (400-550 nm). MLCT emission (λ(max) ≈ 580 nm) in tetrahydrofuran (THF) solution at rt is observed for W(CNXy)6 and W(CNIph)6 with lifetimes of 17 and 73 ns, respectively. Diffusion-controlled energy transfer from electronically excited W(CNIph)6 (*W) to the lowest energy triplet excited state of anthracene (anth) is the dominant quenching pathway in THF solution. Introduction of tetrabutylammonium hexafluorophosphate, [Bu(n)4N][PF6], to the THF solution promotes formation of electron transfer (ET) quenching products, [W(CNIph)6](+) and [anth](•-). ET from *W to benzophenone and cobalticenium also is observed in [Bu(n)4N][PF6]/THF solutions. The estimated reduction potential for the [W(CNIph)6](+)/*W couple is -2.8 V vs Cp2Fe(+/0), establishing W(CNIph)6 as one of the most powerful photoreductants that has been generated with visible light.

Electron transfer from hexameric copper hydrides.

The octahedral core of 84-electron LCuH hexamers does not dissociate appreciably in solution, although their hydride ligands undergo rapid intramolecular rearrangement. The single-electron transfer proposed as an initial step in the reaction of these hexamers with certain substrates has been observed by stopped-flow techniques when [(Ph3P)CuH]6 is treated with a pyridinium cation. The same radical cation has been prepared by the oxidation of [(Ph3P)CuH]6 with Cp*2Fe(+) and its reversible formation observed by cyclic voltammetry; its UV-vis spectrum has been confirmed by spectroelectrochemistry. The 48-electron trimer [(dppbz)CuH]3 has been prepared by use of the chelating ligand 1,2-bis(diphenylphosphino)benzene (dppbz).

Bespoke Photoreductants: Tungsten Arylisocyanides

Modular syntheses of oligoarylisocyanide ligands that are derivatives of 2,6-diisopropylphenyl isocyanide (CNdipp) have been developed; tungsten complexes incorporating these oligoarylisocyanide ligands exhibit intense metal-to-ligand charge-transfer visible absorptions that are red-shifted and more intense than those of the parent W(CNdipp)6 complex. Additionally, these W(CNAr)6 complexes have enhanced excited-state properties, including longer lifetimes and very high quantum yields. The decay kinetics of electronically excited W(CNAr)6 complexes (*W(CNAr)6) show solvent dependences; faster decay is observed in higher dielectric solvents. *W(CNAr)6 lifetimes are temperature dependent, suggestive of a strong coupling nonradiative decay mechanism that promotes repopulation of the ground state. Notably, *W(CNAr)6 complexes are exceptionally strong reductants: [W(CNAr)6](+)/*W(CNAr)6 potentials are more negative than -2.7 V vs [Cp2Fe](+)/Cp2Fe.

Structural Characterization of Zinc Bicarbonate Compounds Relevant to the Mechanism of Action of Carbonic Anhydrase

The tris(3-t-butyl-5-methylpyrazolyl)hydroborato and tris(2-pyridylthio)methyl derivatives, [TpBut,Me]ZnOCO2H and [κ4-Tptm]ZnOCO2H, are the first pair of terminal zinc bicarbonate complexes to be structurally characterized by using X-ray diffraction. In both cases, the bicarbonate ligand coordinates in a unidentate manner, comparable to that in human carbonic anhydrase I. While the bicarbonate complex [κ4-Tptm]ZnOCO2H is obtained by treatment of {[κ3-Tptm]Zn(μ–OH)}2 with CO2 in the presence of water, the bridging carbonate complex [Tptm]Zn(μ-CO3)Zn[Tptm] is obtained in the absence of water. The reactivity of {[κ3-Tptm]Zn(μ–OH)}2 towards CO2 is sufficiently high that the carbonate complex is obtained upon exposure to air.

Molecular Structures of Thimerosal (Merthiolate) and Other Arylthiolate Mercury Alkyl Compounds

The molecular structure of sodium ethylmercury thiosalicylate (also known as thimerosal and Merthiolate) and related arylthiolate mercury alkyl compounds, namely PhSHgMe and PhSHgEt, have been determined by single crystal X-ray diffraction. (1)H NMR spectroscopic studies indicate that the appearance of the (199)Hg mercury satellites of the ethyl group of thimerosal is highly dependent on the magnetic field and the viscosity of the solvent as a consequence of relaxation due to chemical shift anisotropy.