W. Drenth

Homologous series of liquid-crystalline metal free and copper octa-n-alkoxyphthalocyanines

Abstract Two series of discotic liquid crystals, one based on metal-free and the other on copper containing phthalocyanine (Pc) as the central core and eight peripherally n-alkoxy groups (C6–C12) as substituents have been synthesized and their mesomorphic properties and structural parameters have been determined. These compounds represent a series totally devoid of polymorphism, the mesophase in all cases being Dho. In the solid state an orthorhombic two dimensional lattice with four molecules per unit cell and a presumably tilted stacking is present, while in the mesophase the planes of the molecules are on average perpendicular to the direction of the stacks. The aggregation behaviour of the C8, C10 and C12 homologues was studied as a function of solvent polarity and of concentration. The electrical properties of the copper complexes of the n-dodecoxy and n-octoxy derivatives have been determined by means of complex impedance spectroscopy and compared with those of the non-mesogenic CuPc.

Peripherally Octasubstituted Phthalocyanines with Branched Alkoxy Chains

Abstract Phthalocyanines (H2Pc) octasubstituted with branched alkoxy chains were synthesized: 2,3,9,10,16,17,23,24- octakis(3,7-dimethyloctoxy)phthalocyanine (1a) and 2,3,9,10,16,17,23,24-octakis(3,7,11-trimethyldodecoxy)phthalocyanine (1b). Their mesomorphic properties were studied by DSC, polarization microscopy and X-ray diffraction. Compound 1a, which was initially crystalline at room temperature, maintains its mesomorphic structure on cooling back to room temperature. Compound 1b is mesomorphic at room temperature. It shows a D ho→D hd transition at 34[ddot]C and a transition of unknown nature at 173[ddot]C. Both compounds display a D→I transition.

Screw Sense of Polyisocyanides

From steric considerations as well as from an analysis of CD spectra a (P)-screw configuration could be attributed to the (−)-rotating molecules of poly(t-butyl isocyanide).

Luminescence and energy migration in the solid state and in the ordered columnar mesophase of peripherally octa-n-dodecoxy-substituted phthalocyanine

Abstract The luminescence of octa- n -dodecoxy-substituted phthalocyanine has been studied as a function of temperature (4.2-400 K). Quenching occurs down to the lowest temperatures and has a low activation energy. The quenching is mainly due to migration to molecules of the analogous copper complex. At the solid → mesophase transition a sharp drop in luminescence intensity occurs which is explained in terms of a change in the rate of migration to the quenching sites.

Polytopic Ligand Systems - Synthesis and Complexation Properties of a Crowned Phthalocyanine

The synthesis is described of a phthalocyanine that contains four 15-crown-5 rings; K+ ions induce dimerization of the phthalocyanine, whereas Li+ and ButNH3+ ions do not.

Mechanism of olefin epoxidation by a mono-oxygenase model

Kinetic data suggest that the rate determining step in the epoxidation of cyclohexene by Mn-TPP and sodium hypochlorite is the conversion of a Mn(III)-species into an oxo-manganese(V)-species.

Charge separation and recombination in pulse-irradiated columnar aggregates of peripherally octa-n-alkoxy-substituted phthalocyanines

Abstract Large microwave conductivity transients are observed on pulse radiolysis of peripherally octa-n-alkoxy-substituted phthalocyanines both in the solid and liquid-crystalline phases. This is attributed to the formation of mobile charge carriers within the phthalocyanine cores of the columnar aggregates. Charge recombination occurs via intercolumnar electron tunnelling through the intervening hydrocarbon mantle.

A novel enantiopure proline-based organonickel(III) halide monocation with a pentadentate C, N2, O2-bonded bis(ortho-chelating) aryldiamine ligand☆

Abstract An attempt was made to use the enantiopure arylnickel(II) complex [Ni(L ★ − N , C , N )Br], 1 , (L ★ is the monoani ligand, 2,6-bis[(2-( S )-2-isopropoxycarbonyl-1-pyrrolidinyl)methyl)phenyl) as a catalyst for the Kharasch addition reaction of CCl 4 to alkenes which led instead to a new ionic arylnickel(III) complex [Ni(L ★ )Cl] 2 [NiCl 4 ] (=[ 2-Cl ] 2 [NiCl 4 ]. An X-ray diffracti study of this complex revealed the presence of two identical monocations [ 2-Cl ] + that have octahedrally coordinated Ni(III) centres and a single dianionic NiCl 4 2− unit. The octahedral ligand sphere of cation [ 2-Cl ] + is best described as tetragonally compressed, with the meridional coordination comprising N 2 , O 2 donative bonding from the two N atoms of the pyrollidine groups and two carbonyl O atoms of the ester groups of L ★ , the mutually trans apical sites are occupied by a Cl atom and the C atom of the NiC aryl bond; i.e. the monoanionic organic ligand L ★ binds as a monoanionic C, N 2 , O 2 pentadentate system. Spectroscopic data for [ 2-Cl ] + are presented and compared with those for the square-planar arylnickel(II) complex 1 , in which the oxygen donor atoms of the ester groups of L ★ are not coordinated and the ligand thus acts as a C, N 2 terdentate system.

Poly(iminomethylenes). 9. Induction of screw sense in the nickel(II)-catalyzed polymerization of chiral isocyanides

Abstract A rule is presented which predicts the screw sense of the polymers obtained in a nickel(II)catalyzed reaction from chiral isocyanides of the type R1R2R3CNC. It is based on the steric effects and on the ligand properties of R1, R2 and R3. The optical rotation data on ten chiral isocyanides and their polymers verify this rule. The results suggest that the asymmetric induction of screw sense is controlled kinetically at the catalyst center. A thermodynamically controlled process appears to be less likely.

Poly(iminomethylenes). 8. Circular insertion mechanism of nickel(II)-catalyzed polymerization of isocyanides

Abstract A merry-go-round sequence of ligand/insertions is proposed for the polymerization of isocyanides by nickel(II). The mechanism agrees with kinetic results as well as with data on the reactivity of coordinated isocyanides and on substitution at nickel(II).