One‐Dimensional,Cofacial Porphyrin Polymers Formed by Self‐Assembly of meso‐Tetrakis(ERE Donor) Zinc(II) Porphyrins

A series of meso‐tetrakis‐(ERE donor) zinc(II) porphyrins n Zn (ERE donor=4‐R‐3,5‐bis[(E)‐methyl]phenyl; 1 Zn: E=NMe₂, R=Br; 2 Zn: E=NMe₂, R=H; 3 Zn: E=OMe, R=Br; 4 Zn: E=OMe, R=H) have been synthesized in excellent yields. As a result of the combination of a Lewis acidic site and eight Lewis basic sites within one molecule, monomeric molecules of n Zn self‐assemble to form one‐dimensional porphyrin polymers [ n Zn]_∞ in the solid state, as confirmed for 1 Zn and 3 Zn by X‐ray crystallography. The coordination environment around the zinc(II) ions in these polymers is octahedral. They are ligated by four equatorial nitrogen atoms of the porphyrin and two apical E atoms (E=N, O) provided by the EBrE donor groups of adjacent n Zn molecules. Complexes 2 Zn and 4 Zn did not form single crystals, but solid‐state UV/Vis analysis points to the formation of similar structures. Solution UV/Vis and ¹H NMR spectroscopy indicated that interactions between 1 Zn and 2 Zn monomers in the polymers are stronger than between 3 Zn and 4 Zn monomers. Interestingly, they also revealed that the presence of a neighboring bromine atom in the EBrE donor groups has a considerable influence on the coordination properties of the benzylic N or O atoms. The zinc(II) ions of the porphyrins most likely adopt only hexacoordination in the solid state, owing to the unique predisposition of Lewis acidic and basic sites in the n Zn molecules. Several parameters of the aggregates, for example, the interplanar separation between porphyrins and the zinc–zinc distances, change as a function of the coordinating E groups. The high degree of modularity in their synthesis makes these zinc(II) porphyrins an interesting new entry in noncovalent multiporphyrin assemblies.     

Matrix elements of the Coulomb Green function between Slater orbitals

Analytic expressions are given for integrals of the Coulomb Green function with Slater type atomic orbitals. The results involve hypergeometric functions.Supported by the National Institutes of Health, Grant No. GM23223.     

Preparation of polymer colloids by chemical reactions in aerosols. I. Poly(p-tertiarybutylstyrene)

A procedure was developed by which polymer colloids can be prepared by polymerizing aerosol droplets of monomers with an initiator in the vapor state. This work describes the formation of poly(p-tertiarybutylstyrene) particles by exposing the corresponding monomer droplets to trifluoromethanesulfonic acid. It was found that the monomer-to-initiator mass ratio is the critical factor in determining the uniformity and morphology of the particles. Under ideal conditions spheres of narrow size distribution are obtained. Otherwise porous particles or soft particles with whiskers may develop. The aerosol was prepared in a falling film generator, but other procedures for producing monomer droplets may be used.     

An NMR study of the rotational barriers in cobalt-stabilized carbocations: X-ray crystal structures of (η-C4Ph4)Co-(η-C5H4R), where R is CH3CO, CHO, CH(Bu)OH

Treatment of the aldehyde (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-CHO) (4b) with tert-butyllithium or phenyllithium yields the secondary alcohols (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-CH(R)OH), where R=tert-butyl (5) or phenyl (6). Protonation of 5 and 6 at −80 °C furnishes the deep purple, cobalt-stabilized cations, 7 and 8, respectively, both of which exhibit restricted rotation about the external C₅H₄-CHR⁺ linkage on the NMR time-scale. These data indicate a minimum value for the barrier to rotation of 15 kcal mol⁻¹, but it is certainly much higher, indicating a considerable degree of C-C double bond character. X-ray crystal structures of 4b, 5 and also of the ketone (η⁴-C₄Ph₄)Co(η⁵-C₅H₄-C(O)CH₃ (4a) are reported. The secondary alcohol 5 exhibits disorder in the solid state because of the presence of diastereomers as a consequence of the stereogenic center at the α-carbon and the clockwise or anticlockwise propeller orientations of the tetraphenylcyclobutadiene ligand.     

Photophysical properties of a C6 hydrocarbon linked porphyrin dimer

The synthesis and characterisation of a C₆ hydrocarbon linked porphyrin dimer and its zinc complex is described. From fluorescence quantum yields and excited singlet and triplet state lifetimes, recorded for the dimers and the corresponding monomer species, it is suggested that the dimeric porphyrins exist in solution in open and closed conformations. The open conformations retain photophysical properties similar to those of the relevant monomeric species but the closed conformations do not fluoresce.     

Mediated amperometric biosensors for d-galactose,glycolate and l-amino acids based on a ferrocene-modified carbon paste electrode

Direct-current cyclic voltammetry is used to investigate the suitability of a ferrocene derivative as a mediator with galactose, glycolate and l-amino acid oxidases. The three enzymes coupled catalytically to ferrocene monocarboxylic acid exhibiting homogeneous second-order rate constants in the range 0.4 × 10⁵ to 8.5 × 10⁵ l mol^?1 s^?1. Enzyme electrodes which responded to d-galactose, glycolate or l-amino acids were constructed. The appropriate oxidase was retained behind a dialysis membrane at a carbon paste electrode containing the poorly soluble derivative 1,1′-dimethylferrocene. All the electrodes responded rapidly to millimolar concentrations of their respective substrates producing 95% of the steady-state current response in <2 min. This general method of biosensor construction should be widely applicable to oxidases and other oxidoreductase enzymes.     

Bismuth-catalyzed benzylic oxidations with tert-butyl hydroperoxide

[reaction: see text] Oxidation of alkyl and cycloalkyl arenes with tert-butyl hydroperoxide catalyzed by bismuth and picolinic acid in pyridine and acetic acid gave the corresponding benzylic ketones (48-99%). Alternatively, oxidation of methyl arenes gave the corresponding substituted benzoic acids (50-95%). Preliminary mechanistic studies were consistent with a radical mechanism rather than a bismuth(III)-bismuth(V) cycle.     

Translational-energy spectroscopy of NO+ and NO2+

High-resolution translational-energy spectroscopy (up to 0.1 eV) has been carried out on 8

V beams of NO^? and NO^2?. Several features in the spectrum of NO⁴ are assigned to the transitions within the triplet manifold of this ion. The observed transitions originate in several excited electronic states, indicating long lifetimes (> 10 μs) for the states involved. Two electronic transitions in NO²' have been observed at low energies which are attributed to excitations to the first two excited states of this ion.     

Selective alkylation and Suzuki coupling as an efficient strategy for introducing functional anchors to the ethylene-bis(indenyl) ligand

Chiral ansa-ethylene-bis(indenyl)-metal complexes, EBI-MX₂, are useful pre-catalysts for a wide variety of reactions, including hydrogenations, hydrosilylations, and polymerization reactions. In order to immobilize these complexes onto heterogeneous supports, a new methodology was developed to introduce functional anchors to the ethylene-bis(indenyl) ligand, EBI. This was accomplished by selective alkylation of indene to form toluene-4-sulfonic acid 2-(3H-inden-1-yl)-ethyl ester, which was then used to alkylate 6-bromoindene. The selective introduction of an aryl bromide then undergoes coupling reactions with aryl borates via the Suzuki coupling to efficiently introduce an alkenyl or alcohol, functional anchor in a simple four step synthesis.     

Structural features of organic anions: 7-Norbornadienyllithium

The structure of 7-norbornadienyllithium, a homoantiaromatic carbanion, is investigated with the semiempirical MNDO molecular orbital method. Alkene out-of-plane bendings persist even when the metal is fully solvated. The structural integrity of the monomer is retained in the dimer and solvated dimer; previously proposed dimers are inconsistent with lithium bonding and are not minimum energy structures on the MNDO hypersurface.