Stereoselective synthesis of chiral pinene[5,6]bipyridine ligands and their coordination chemistry.

The C(2)-symmetric chiral pinene[5,6]bipyridine V (Chart 1) was synthesized according to a procedure published by our group recently (Kolp, B.; Abeln, D.; Stoeckli-Evans, H.; Zelewsky, A. v. Eur. J. Inorg. Chem. 2001, 1207). A series of stereoselectively alkylated derivatives (Va-Vo) (Table 1) was prepared. The solid-state structures of the compounds Vc and Vk were determined by single-crystal X-ray diffraction, where both compounds show a transoid conformation of the bipyridine unit and proved to be alkylated stereoselectively from the sterically less hindered side of the pinene moiety. The X-ray structure of the cobalt complex 4 shows the metal ion to be tetrahedrally coordinated by one chiral bipyridine V and two chloride ligands. If 2 equiv of ligand V was used, 2:1 complexes were obtained with Cu(I), Ag(I), and Co(II) ions.

Crystal structure analysis and chiral recognition study of Delta-[Ru(bpy)2(py)2][(+)-O,O'-dibenzoylD-tartrate].12H2O and Lambda-[Ru(bpy)2(py)2][(-)-O,O'-dibenzoyl-L-tartrate].12H2O.

The molecular structure and crystal-packing mode of the enantiopure chiral building blocks Delta-[Ru(bpy)(2)(py)(2)][(+)-O,O'-dibenzoyl-D-tartrate].12H(2)O (I) and Lambda-[Ru(bpy)(2)(py)(2)][(-)-O,O'-dibenzoyl-L-tartrate].12H(2)O (II) have been determined by single-crystal X-ray diffraction data. This study proposes a model of how the L- and D-dibenzoyltartrate anions recognize the chirality of the hydrophobic [Ru(bpy)(2)(py)(2)](2+) complex. The monoclinic unit cell contains four complex cations, four tartrate anions, and 48 water molecules. Since there are no possibilities to form hydrogen bonds between the cations and anions, chiral recognition is due to crystal packing. Two benzoyl rings of two different tartrate anions are gripping the two bpy-planes of the Ru-complex. Further a third benzoyl ring from a tartrate anion is packed between the two pyridine rings, favoring one enantiomeric form to crystallize from aqueous solution. Crystal structure data for I at 153 K: a = 15.342(3) A, b = 19.200(4) A, c = 18.872(4) A, beta = 104.841(3) degrees, monoclinic space group C(2), R(1)= 0.0239 (I > 2sigma(I)), R(2) = 0.0606, Flack parameter = 0.0115 (with esd 0.0166). For II at 293 K: a = 15.376(4) A, b = 19.388(11) A, c = 19.085(7) A, beta = 105.11(2) degrees, monoclinic space group C121, R(1)= 0.0686 (I > 2sigma(I)), R(2) = 0.1819, Flack parameter = -0.0100 (with esd 0.0521).

Self-assembly of multinuclear coordination species with chiral bipyridine ligands: silver complexes of 5,6-CHIRAGEN(o,m,p-xylidene) ligands and equilibrium behaviour in solution.

The complexation reactions between Ag- and a series of enantiopure ligands belonging to the CHIRAGEN (from CHIRAlity GENerator) family (L1, L2, L3, based on (-)-5,6-pinene bipyridine) have been studied in solution. It has been shown that the length of the bridge plays a fundamental role in the self-assembly processes leading to different compounds: mononuclear complexes (with L3), mixtures of polynuclear complexes (with L2) and circular helicates (with L 1). Although the absolute configuration of the chiral centres in all three ligands is the same, the metal-centred chirality of L3 (delta) is inverted with respect to that in the other two complexes with L1 and L2 (delta). The metal configuration is thus opposite in the mononuclear complex with respect to the polynuclear species. Detailed thermodynamic studies were carried out for the Ag+ and L1 ligand system by 1H and 109Ag NMR spectroscopy (as a function of concentration, temperature and pressure). At low temperature and high pressure, the [Ag6L1(6)]6+ hexanuclear circular helicate forms a tetranuclear circular helicate [Ag4L1(4)]4+: 2[Ag6L1(6)]6+ <=> 3 [Ag4L1(4)]4+. The thermodynamics parameters, obtained by temperature and pressure variation, have the following values: K298 = (8.7 +/- 0.7) x 10(-5) mol x kg(-1), deltaHo = -15.65 +/- 0.8 kJ x mol(-1), deltaSo = -130.2 +/- 3 J x mol(-1) x K(-1) and deltaVo(256 K)= -160 +/- 12 cm3 x mol(-1). The reaction volume calculated according to Connolly's method indicates that the calculated structure of [Ag4L1(4)]4+ is plausible. Both the signs and large magnitudes of deltaSo and deltaVo are counterintuitive, yet can be understood by modelling methods.

Predetermined chirality at metal centers of various coordination geometries: a chiral cleft ligand for tetrahedral (T-4), square-planar (SP-4), trigonal-bipyramidal (TB-5), square-pyramidal (SPY-5), and octahedral (OC-6) complexes

Two tetradentate bispinene-bipyridine type ligands, each with six stereogenic carbon centers, were synthesized from (-)-alpha-pinene. Their ability to predetermine chiral configurations at metal centers was studied. The two diastereoisomers, L1 and L2, differ in their absolute configuration at the bridgehead position. These ligands form metal complexes with Ag(I), Pd(II), Zn(II), Cu(II), and Cd(II), with coordination numbers four, five, and six and with complete control of chirality at the metal centers. Using L1 rather than L2 leads to complexes of inverted absolute configuration at the metal centers. These diastereomeric coordination species can be obtained either as separate compounds or, in some cases, as solids containing them in a 1:1 ratio. Ligands L1 and L2 thus show that the pinene-bipyridines are versatile molecules for the formation of metal complexes with predetermined chirality. In all cases, absolute configurations were determined in the solid state by X-ray diffraction methods and in solution by CD spectroscopy. The sign of exciton couplets from the pi-pi* transitions always agrees with the expectations for a given local configuration at the metal center. The five-coordinate, inherently chiral species of Zn(II) and Cu(II) described in this article are the first examples of trigonal-bipyramidal metal complexes with predetermined absolute configuration containing topologically linear ligands.

Stereoselective Synthesis of Coordination Compounds: Self-Assembly of a Polymeric Double Helix with Controlled Chirality.

Its information content is infinitely smaller than that of DNA, but its structure (see picture) ressembles the double-stranded helix produced by nature. This self-assembled, configurationally predetermined coordination polymer is built up from enantiopure chiral bipyridine-type ligands and silver ions.