New Coordination Compounds for Photochemical Purposes and Beyond

A general account is given of the synthetic research carried out in the field of coordination chemistry in one group in the Institute of Inorganic Chemistry in Fribourg. With the goal of synthesizing artificial structures, which can function as photochemical molecular devices, several synthetic strategies for multicenter coordination species are mentioned. It is reported, that the molecules, which have been designed to form coordination compounds with predefined chiralities of the central metal, can also be used as ligands in enantioselective catalysis

On the Way towards New Materials: Metal Complexes as Building Blocks

Two related directions of materials research are described: i) The synthesis of photonic materials, based on transition-metal compounds mainly with ruthenium and osmium as the photoactive centers. The devices envisaged are antenna molecules, molecular wires, photon-activated switches, and molecules performing other logical functions. ii) The development of a strategy for the synthesis of complex coordination species suitable for molecular devices, based on modular synthons, where a special emphasis is put on the stereochemical aspect of the fragments employed. This strategy is based on a new family of chiral pyridine and bipyridine ligands that are useful for the construction of inert building blocks, as well as in self-assembly processes leading to highly organized systems

1,2-Bis(3-hydroxy­benzyl­idene)diazane

The asymmetric unit of the title compound, C14H12N2O2, which was synthesized unexpectedly by refluxing an ethano­lic solution of isonicotinic hydrazide and 3-hydroxy­benzaldehyde, contains one half-mol­ecule with the center of the N—N bond lying on a crystallographic center of inversion. In the crystal structure, mol­ecules are linked by inter­molecular O—H⋯N hydrogen bonds into an infinite layer structure parallel to (110)

Diastereoselective synthesis of coordination compounds: a chiral tripodal ligand based on bipyridine units and its ruthenium(II) and iron(II) complexes

The enantiomerically pure chiral tris-chelating ligand (+)-(7S,10R)-L(L) comprising three 4,5-pinenobipyridine subunits connected through a mesityl spacer has been synthesized. Complexes of L with RuII and FeII have been prepared and characterised. NMR spectroscopy indicates that only one diastereoisomer is formed, and the CD spectra show that the complexes have the Λ configuration on the metal centre. The X-ray crystal structure of the iron complex shows that in the octahedral complex, the ligand L coils around the metal and confirms the absolute configuration. The RuII and FeII compounds were also characterised by mass spectrometry, electronic absorption, and, in the case of Ru(II), fluorescence spectroscopy. The photostability of the ruthenium compound was checked by photochemical experiments

Novel Polypyridyl Ruthenium(II) Complexes Containing Oxalamidines as Ligands.

The complexes [Ru(bpy)2(H2TPOA)](PF6)2 ⋅ 4H2O, (1); [Ru(Me-bpy)2(H2TPOA)](PF6)2 ⋅ 2H2O, (2); [Ru(bpy)2(H2TTOA)](PF6)2 ⋅ 2H2O, (3); [Ru(Me-bpy)2(H2TTOA)](PF6)2 ⋅ 2H2O, (4) and {[Ru(bpy)2]2(TPOA)}(PF6)2 ⋅ 2H2O, (5) (where bpy is 2,2´bipyridine; Me-bpy is 4,4´- dimethyl-2,2´-bipyridine; H2TPOA is N, N´, N´´, N´´´- tetraphenyloxalamidine; H2TTOA is N, N´, N´´, N´´´- tetratolyloxalamidine) have been synthesized and characterized by 1H-NMR, FAB-MS, infrared spectroscopy and elemental analysis. The X-ray investigation shows the coordination of the still protonated oxalamidine moiety via the 1,2−diimine unit. The dimeric compound (5) could be separated in its diastereoisomers (5´) and (5´´) by repeated recrystallisation. The diastereomeric forms exhibit different 1H-NMR spectra and slightly shifted electronic spectra. Compared with the model compound [Ru(bpy)3]2+, the absorption maxima of (1)–(5) are shifted to lower energies. The mononuclear complexes show Ru(III/II)- couples at about 0.9 V vs SCE, while for the dinuclear complex two well defined metal based redox couples are observed at 0.45 and 0.65 V indicating substantial interaction between the two metal centres

Aqua­azido­{2,2′-[o-phenylenebis(nitrilo­methyl­idyne)]diphenolato}manganese(III) hemihydrate

In the title compound, [Mn(C20H14N2O2)(N3)(H2O)]·0.5H2O, the MnIII ion is chelated by the N,N′,O,O′-tetra­dentate Schiff base ligand and further coordinated by one azide ion and one water mol­ecule in trans positions, resulting in a distorted fac-MnN3O3 octa­hedral arrangement. The O atom of the uncoordinated water mol­ecule lies on a crystallographic twofold axis. In the crystal, O—H⋯O and O—H⋯N hydrogen bonds help to establish the packing

The Bright Future of Stereoselective Synthesis of Coordination Compounds

Transfer of chirality during the build-up of molecules has been applied innumerable times in organic chemistry since the end of the 19th century, when it was introduced in the so-called asymmetric synthesis by E. Fischer. Although analogous reactions were introduced in co-ordination chemistry in its early development, diastereoselective reactions have not been applied in a very systematic way for co-ordination species. The highly versatile co-ordination geometry of metal centres makes the synthesis of a selected stereoisomer in general a formidable task. In the present article an account on new developments in the field is given, focussing on recently synthesized molecules, where natural chiral products are used to create a large number of chiral ligands which predetermine the chirality at metal centres

Synthesis and Stereochemical Properties of Chiral Square Complexes of Iron(II)

Der hexadentate und ditopische Ligand 2,5-Bis([2,2']bipyridin-6-yl)pyrazin bildet bei der Selbstorganisationsreaktion mit Fe²⁺-Ionen einen chiralen, quadratförmigen Tetramerkomplex. Das Racemat dieses Komplexes wurde mit Hilfe von Antimonyltartrat in die Enantiomere getrennt. Die Reinheit des Enantiomers wurde durch NMR-Spektroskopie unter Zuhilfenahme eines chiralen, diamagnetischen Shift-Reagenzes untersucht, wie auch duch die Beobachtung des Circulardichroismus (CD). Das CD-Spektrum wurde zudem mit zeitabhängiger Dichtefunktionaltheorie berechnet, wobei die vorhergesagte Korrelation zwischen CD-Spektrum und Konfiguration des Komplexes durch Röntgenstrukturanalyse bestätigt wurde. Die Verwendung einer chiralisierten Variante des Liganden ergab den entsprechenden Eisenkomplex in diastereomerenreiner Form.The hexadentate, and ditopic ligand 2,5-bis([2,2']bipyridin-6-yl)pyrazine yields a chiral, tetrameric, square-shaped, self-assembled species upon complexation with Fe²⁺ ions. The racemate of this complex was resolved with antimonyl tatrate as the chiral auxiliary. The purity of the enantiomer was determined by NMR spectroscopy, by using a chiral, diamagnetic shift reagent, and by circular dichroism (CD). The CD spectrum was also calculated by time-dependent density functional theory, and the correlation that was found between CD spectrum and configuration was confirmed by X-ray cristallography. When a chiralised version of the ligand was used instead, the corresponding iron complex was obtained in diastereomerically pure form