Dennis V. Stynes

Phthalocyanine sensitized reduction of methyl viologen using visible light

Abstract A detailed study is reported of the ability of a range of metallophthalocyanines to photoreduce methylviologen, in the presence of triethanolamine. Certain species are demonstrated to be effective photocatalysts, using light of wavelength corresponding to the Q band in their electronic spectrum. However quantum yields are very low. Other metallophthalocyanines are shown to be inactive under similar conditions. Using electrochemical and spectroscopic data the energies of the photoactive states are estimated. From these results the thermodynamic driving forces for both oxidative and reductive quenching are calculated, together with the thermal following and back reactions. By comparison with other photoactive systems, with known kinetic data, it is demonstrated that the thermodynamic data are a useful guide to photoactivity when kinetic data are unavailable.

Bis(2,2′-bipyridine)(1,2-diimino-9,10-anthraquinone)ruthenium(II): a complex containing an exceptionally strong π-accepting α-α′ diimine ligand I. Synthesis, crystal and electronic structures

Abstract The compound 1,2-diamino-9,10-anthraquinone (DAAQ) binds to ruthenium bis-(2,2′-bipyridine) forming a complex containing the oxidized 1,2-diimino-9,10-anthraquinone (DIAQ). The complex was crystallized as [Ru(bpy)2DIAQ](1,3-benzenedisulfonate)·6.5H2O. Crystal data: triclinic, space group P1−, a = 10.095(2) A , b = 12.035(2) A , c = 17.652(4) A , α = 97.50(3)°, β = 92.54(3)°, γ = 91.65(3)° , Z = 2 . The metal is bound to the diimine site of the DIAQ ligand. There is an extensive n backbonding interaction between the DIAQ ligand and the metal as inferred from theoretical calculations, electrochemical and spectroscopic data. The DIAQ is the best a accepting neutral α-α′ diimine ligand known to date.

Iron complexes of borylated vicinal dioxime macrocycles

Abstract Metal complexes of the general form trans -FeN 4 LL′, where N 4 is a planar tetradentate macrocycle and L and L′ axial monodentate ligands form an important class of inorganic substances. This review summarizes the chemistry of low spin Fe(II) and μ-oxo Fe(III) complexes containing vicinal dioximate ligands with emphasis on the borylated forms; Fe(DMGBF 2 ) 2 , Fe(DMGBPh 2 ) 2 , Fe(BQDBF 2 ) 2 , Fe(NPQBF 2 ) 2 . An extensive range of binding affinities, ligand labilities, MLCT spectra, and redox potential may be achieved by variation in L, N 4 , and BR 2 groups. Structural and ligand binding data for Fe(II) and μ-oxo Fe(III) complexes are discussed. The Fe(DMGBR 2 ) 2 complexes adopt either a C 2 ν or C 2h conformation depending upon the axial ligands present. Applications to the measurement, understanding, and use of nonbonded interactions are described.

Syntheses, characterization and structures of 2-(2-pyridyl)-4-methylcarboxyquinoline ligand and bis(2,2′-bipyridine)-2-(2-pyridyl)-4-methylcarboxyquinoline ruthenium (II) hexafluorophosphate

Abstract The synthesis, characterization and X-ray single crystal structure of a 2-(2-pyridyl)-4-methylcarboxyquinoline diimine ligand (pqme) and its corresponding bis(2,2′-bipyridine)-2-(2-pyridyl)-4-methylcarboxyquinoline ruthenium (II) hexafluorophosphate Ru(bpy)2(pqme)(PF6)2 complex is described. 1H, 1H–1H COSY, 1H–1H TOCSY, 13C NMR, FT-IR, elemental and mass spectrometric analyses were used to characterize the products and fully ascertain their structures. The complex exhibited two well-resolved MLCT transitions in the visible region and a ligand-based transition in the UV region. The cyclic voltammogram of the complex showed a reversible Ru(III)/Ru(II) couple and three well-defined ligand-based reductions. X-ray diffraction analyses provided further insight as to the conformations and geometry of both products. A trans conformation is shown in the solid state as expected for the 2-(2-pyridyl)-4-methylcarboxyquinoline ligand, and a distorted octahedral geometry for the bis(2,2′-bipyridyl)-2-(2-pyridyl)-4-methylcarboxyquinoline ruthenium (II) hexafluorophosphate complex due to α hydrogens of the opposing N–N ligands have been revealed.

Ligand substitution pathways in carbonyl complexes of Fe(dmgBF2)2 with trans weak donor, sterically hindered and anionic ligands

Abstract The effects of weak donor ligands CH 3 CN, dmso, dmf, thf, the sterically hindered ligand 2-methylimidazole (2-MeIm) and anionic ligands CN − , Cl − , Br − , on the axial ligation reactions of trans -FeN 4 L(CO) complexes are described (N 4 =the tetradentate macrocyclic ligand bis-difluoro(dimethylglyoximato)- borate). In reactions with 1-methylimidazole (MeIm) in dichloromethane solution two dissociative paths (CO and L loss) contribute for the weak donors but only the CO loss path is important for the anionic or sterically hindered ligands studied. The relative binding constants of L to FeN 4 (CH 3 CN) 2 in CH 3 CN or CH 2 Cl 2 solution are CN − >MeIm>py>2-MeIm⪢Cl − >Br − >CH 3 CN and relative rates of CO dissociation trans to L are CN − , MeIm 3 CN, 2-MeIm − , Br − .

Binuclear trans-μ-pyrazine-bis­[bromo­tetra­pyridine­ruthenium(II)] dihexa­fluoro­phosphate di­methyl­form­amide disolvate

The Ru atoms of the title compound, [Ru2Br2(C4H4N2)(C5H5N)8](PF6)2.2C3H7NO, are coordinated by the four N atoms of the pyridine (py) ligands and a bromide. Two such units are bridged by a pyrazine (pz) unit, which is disposed about a centre of inversion, so as to form a trans pseudo-octahedral geometry about Ru. The py units are in an eclipsed conformation when viewed down the internuclear axis. The Ru—N(pz) distance is 2.079 (3) A, while the Ru—Br distance is 2.5524 (4) A.

Crystal Structure and Molecular Modeling of 4,4'-Bi-4H-cyclopenta(def)phenanthrenylidene and Related Derivatives

The twisted pentafulvene, 4,4′-bi-4H-cyclopenta[def]phenanthrylidene, does not undergo oxidative electrocyclization to a semibuckminsterfullerene under photo-oxidative conditions. However, the use of standard dehydrogenating agents such as DDQ or tetrachloro-2,3-benzoquinone at 200°C resulted in partial oxidative electrocyclization and formation of a Diels–Alder adduct, respectively. The crystal structure of this Diels-Alder adduct was obtained and shown to possess C2 symmetry. The crystal structure for 4,4′-bi-4H-cyclopenta[def]phenanthrylidene was also obtained and the molecular parameters differ slightly from what was previously reported for the same compound. Molecular modeling of this pentafulvene gave a twist angle matching the crystal structure. Similar modeling of related bifluorenylidene, bis-1,1′-indenylidenes and biscyclopentadienylidene gave twist angles which correlate with the computed heats of hydrogenation for the bridging alkene unit.

ISOMER ELUCIDATION IN MONO- AND BINUCLEAR 1,4-DIISOCYANOBENZENE DERIVATIVES OF FERROUS BIS-NAPHTHOQUINONE DIOXIME

Abstract The syntheses of mononuclear and binuclear derivatives of low spin ferrous naphthoquinone dioxime complexes containing the axial ligand 1,4-diisocyanobenzene (DIB) are described. Chromatographic separation and nmr characterization of sym and asym isomers of Fe(NPQH)2(Py)(DIB) as well as two of three possible isomers for [Fe(NPQH)2Py]2(DIB) are described. Kinetic factors effecting the yields of mono vs binuclear species are elucidated.

Carbon monoxide and isocyanide binding to iron(II) complexes of tetradentate bis di-imine and bis di-oxime and mixed oxime-imine macrocycles

The synthesis and characterization of new low spin Fe(II) complexes of diacetylmonoximeiminodiacetylmonoximato-1,3 propane (DOHpn), and ethane (DOHen), and of 2,3,9,10 tetramethyl 1,4,8,11 tetraazacyclotetradeca 1,3,8,10 tetraene (TIM) are reported; [Fe(N4)(CH3Im)X](PF6)2 X = CH3Im, CO, and benzylisocyanide (BZNC). Kinetic studies for CO and BZNC dissociation are compared with corresponding data for analogous FeN4 systems. The relative lability if CO is DMGH < DOHpn < DOHen < TIM, TAAB, 14-ane < Porphyrin, Phthalocyanine < 15-ane. Trans effects of CO and BZNC are discussed.