Silvia Schaffner

An element of surprise - efficient copper-functionalized dye-sensitized solar cells

Dye-sensitized solar cells with carboxylate-derivatized {Cu(I)L(2)} complexes are surprisingly efficient and offer a long-term alternative approach to ruthenium-functionalized systems.

Chiral Phosphinopyrrolyl-Oxazolines: A New Class of Easily Prepared, Modular P,N-Ligands

Chiral 2-(N-phosphinopyrrol-2-2)oxazolines (PyrPHOX ligands) are readily prepared from 2-cyanopyrrole by condensation with a chiral amino alcohol and subsequent reaction with dialkyl- or diaryl-chlorophosphines. Iridium complexes of these ligands proved to be highly efficient catalysts for the enantioselective hydrogenation of olefins. With unfunctionalized arylalkenes and ethyl cinnamate enantiomeric excesses of 70–99% were obtained.

In search of enantioselective catalysts for the Henry reaction: are two metal centres better than one?

Catalysts for the asymmetric Henry reaction involving copper(II) complexes of the chiral Schiff bases N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(3-hydroxysalicylideneamine) (H21) and N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(3-ethoxysalicylideneamine) (H22), and H23, which is the reduced analogue of H21, have been studied. Whereas [Cu(1)] and [Cu(2)] give poor yields and enantioselectivity, [Cu(3)] produced moderate to high yields and enantioselectivities were optimal when reactions were carried out in toluene rather than a polar solvent. A significant finding is that both yield and enantioselectivity are enhanced when a second equivalent of Cu(OAc)2 is added to the catalyst. The single-crystal structures of [Cu(3)] and [Cu(1)(H2O)] are presented, and the host–guest interactions and molecular packing in the latter are compared with those in [Cu(2)(H2O)].

A one-dimensional copper(II) coordination polymer containing [Fe(pytpy)2]2+ (pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) as an expanded 4,4′-bipyridine ligand : a hydrogen-bonded network penetrated by rod-like polymers

The one-dimensional coordination polymer [{(H2O)(NO3)2CuFe(1)2}2(NO3)4·2.15MeCN·5.85H2O]n assembles when the pendant pyridine donors in [Fe(1)2]2+ (1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) are treated with Cu(NO3)2·3H2O, exemplifying [Fe(1)2]2+ as an expanded 4,4′-bipyridine ligand. In the solid state, the polymer chains are threaded through hydrogen-bonded macrocycles comprising coordinated and non-coordinated water molecules and nitrate ions, the macrocycles being motifs within interconnected sheets in the structure.

2,2′:6′,2″-Terpyridine-4′(1′H)-thione: a missing link in metallosupramolecular chemistry

The compound 2,2′:6′,2″-terpyridine-4′(1′H)-thione 1 has been prepared and structurally characterised; in both the solid state and in solution, the thione tautomer is dominant. Compound 1 is a key entry into 4′-sulfur-functionalised tpy ligands and a representative alkylation with an electrophilic Frechet dendrimer is presented and the structural characterisation of the new ligand 4 reported. Oxidation of 1 yields bis(2,2′:6′,2″-terpyridin-4′-yl)disulfide 2 which is a novel homoditopic tpy ligand and which forms a tetranuclear [4 + 4] iron(II) metallomacrocycle. Structural characterisation of 2 and preliminary data for the iron complex are presented.

Enantioselective catalysts for the Henry reaction: fine-tuning the catalytic components

Catalysts for the asymmetric Henry reaction involving 1,6-bis(3-ethoxy-2-hydroxyphenyl)-(3S,4S)-(−)-diphenyl-2,5-diazahexane (H22) and copper salts have been investigated. Conditions for the conversion of 4-nitrobenzaldehyde to 2-nitro-1-(4-nitrophenyl)ethanol by reaction with nitromethane have been optimized (5 mol% H22, 10 mol% CuI, THF, 295 K and 2 hours or 273 K and 12 hours) resulting in 99% yield and 90–92% ee. These catalytic conditions are effective for other aromatic aldehydes containing electron-withdrawing substituents, and for pyridine carbaldehydes; representative aliphatic aldehydes were converted to the respective β-hydroxynitro derivatives with good enantioselectivities, and in moderate yields. These catalytic conditions were found to be ineffective for simple aromatic aldehydes or those containing electron-releasing substituents.

Planar chiral asymmetric naphthalenediimide cyclophanes: synthesis, characterization and tunable FRET properties

A series of planar chiral asymmetric naphthalenediimide (NDI) cyclophanes () consisting of two different NDIs interlinked by rigid meta-dimethylenebenzene spacers was synthesized. A modular synthetic strategy based on the dichloro cyclophane as common precursor gave a straightforward access to racemic mixtures of the NDI cyclophane dyes . In particular the substitution of both chlorine atoms of by tert-butylsulfanyl-, methoxy- and piperidinyl-groups provided racemic mixtures of the fluorescent NDI cyclophane dyes , and respectively. Fluorescence spectroscopy revealed chemically tuneable intramolecular FRET properties, as the spectral overlap between the emission of the unsubstituted NDI and the absorption of the core-substituted NDI subunit of the cyclophane could be adjusted by the core substituents. The racemic nature of the samples of cyclophanes , and in the case of the di-tert-butylsulfanyl functionalized cyclophane the enrichment of both enantiomers, was demonstrated by HPLC using a chiral stationary phase. The solid state structure of was determined by X-ray analysis. A periodic arrangement of both enantiomers of the planar chiral cyclophane in pillars such that NDI- and 2,6-core substituted NDI chromophores alternate periodically was observed.

Hierarchical multicomponent assembly utilizing sequential metal–ligand and hydrogen-bonding interactions

The solid state structures of the copper(II) Schiff base complexes [{Cu(1)}(H2O)], [Cu(1)(OH2)]·MeCN and [({Cu(1)}(H2O))2(2)] (H21 = N,N′-(1R,2R)-(–)-1,2-cyclohexylenebis(3-ethoxysalicylideneamine) and 2 = naphthalene-2,6-dicarboxylic acid) exhibit two recurring structural motifs: host–guest, hydrogen-bonded recognition of H2O in the O,O′,O″,O‴-cavity of [Cu(1)], and face-to-face stacking of [Cu(1)] units with non-bonded Cu⋯Cu separations of 3.54–4.89 A. In [{Cu(1)}(H2O)], the H2O molecule is non-coordinated to the copper(II) centre whereas in [Cu(1)(OH2)]·MeCN it is axially bound to the copper(II) atom while retaining its role as a hydrogen-bonded guest in the O,O′,O″,O‴-cavity of an adjacent [Cu(1)] molecule. The guest H2O molecule in [{Cu(1)}(H2O)] can function as a hydrogen bond donor as illustrated by the assembly of [({Cu(1)}(H2O))2(2)]. Solution (in THF) electronic spectroscopic data for the complexes are consistent with dissociation of the building blocks including the cleavage of the Cu–OH2 coordination bond. The self-assembly and structural diversity are discussed in terms of a series of hierarchical events.

The conjugate acid of bis{4′-(4-pyridyl)-2,2′:6′,2″-terpyridine}iron(II) as a self-complementary hydrogen-bonded building block

The protonation of [Fe(1)2]2+, where 1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, generates a trication which forms a one-dimensional, hydrogen-bonded polymer. The single crystal structures of [Fe(1)(H1)][Fe(NCS)6]·2H2O, [Fe(1)(H1)][Fe(NCS)6]·MeCN and [Fe(1)(H1)][ClO4]3·EtOH are reported and illustrate that the packing of the {[Fe(1)(H1)]3+}n chains in the solid state can be modulated by changing the steric demands of the counter-ion. Subtle changes in packing on going from [Fe(1)(H1)][Fe(NCS)6]·2H2O to [Fe(1)(H1)][Fe(NCS)6]·MeCN result in a reorientation of the pendant pyridine rings with respect to the central pyridine ring of the tpy unit in [Fe(1)(H1)]3+.

Conformationally-locked metallomacrocycles—prototypes for a novel type of axial chirality

A series of ditopic ligands incorporating two 2,2′:6′,2″-terpyridine (tpy) metal-binding domains linked to a central naphthalenediyl core by ethyleneoxy chains of various lengths have been prepared and their iron(II) complexes prepared. The major thermodynamic products of complexation are ferracycles of [1 + 1], [2 + 2] or [3 + 3] stoichiometry. In the case of the [1 + 1] complexes, the linker between the two tpy domains is spatially restricted and the cations exhibit chirality associated with the conformation about the central N–Fe–N bonds. The dynamic processes by which the enantiomeric forms interconvert are investigated in the presence of chiral anions by NMR and circular dichroism spectroscopy making use of the Pfeiffer effect. We have shown that ditopic bis(2,2′:6′,2″-terpyridine) ligands give rise to conformationally restricted complexes with iron(II) centres. The absolute configuration of the cations in the diastereomeric ion pairs obtained through the Pfeiffer effect has been calculated using TDDFT methods.