Frieder Jäkle

9,10-Dihydro-9,10-diboraanthracene: supramolecular structure and use as a building block for luminescent conjugated polymers.

Building bridges: The title compound forms an unprecedented polymeric structure with bridging B-H-B three-center two-electron bonds in the solid state. This organoborane serves as an efficient precursor for the preparation of boron-doped pi-conjugated polymers by hydroboration polymerization with a functionalized 1,4-diethynylbenzene (see picture). These polymers form thin films that show intense green luminescence.

Boron-containing polymers as versatile building blocks for functional nanostructured materials

This review aims to highlight recent advances in the emerging field of boron-containing polymers as precursors for nanostructured materials. Boron compounds display highly interesting physical and chemical properties, which are of great potential benefit in the field of materials science. Specifically, combination of the unique characteristics of boron-containing functional groups with the nano-size regime of dendritic structures and the self-assembly of polymers of well-defined architectures, such as telechelic polymers and block copolymers, allows scientists to develop next generation materials for sensing, electronic devices, catalysis, biomedical applications, etc.

Universal Scaffold for Fluorescent Conjugated Organoborane Polymers

Pimp my polymer: A new versatile and strongly emissive conjugated polymer scaffold results when nucleophiles replace the labile bromine atoms on the fluorenylborane polymer backbone (see picture). Such modification allows facile tuning of the stability, thermal characteristics, and photophysical behavior of a diverse range of luminescent polymers with interesting optoelectronic properties and anion-binding behavior.

Regioregular synthesis of azaborine oligomers and a polymer with a syn conformation stabilized by N-H⋅⋅⋅π interactions.

The regioregular synthesis of the first azaborine oligomers and a corresponding conjugated polymer was accomplished by Suzuki-Miyaura coupling methods. An almost perfectly coplanar syn arrangement of the heterocycles was deduced from an X-ray crystal structure of the dimer, which also suggested that NH⋅⋅⋅π interactions play an important role. Computational studies further supported these experimental observations and indicated that the electronic structure of the longer azaborine oligomers and polymer resembles that of poly(cyclohexadiene) more than poly(p-phenylene). A comparison of the absorption and emission properties of the polymer with those of the oligomers revealed dramatic bathochromic shifts upon chain elongation, thus suggesting highly effective extension of conjugation.

Applying the Oligomer Approach to Luminescent Conjugated Organoboranes

A series of highly luminescent monodisperse fluoreneborane oligomers (n=1-6) were prepared using a new iterative synthetic procedure that takes advantage of the highly selective and differential reactivity of bromoboranes with arylsilanes and arylstannanes. Cyclic and square wave voltammetry revealed a gradual decrease of the LUMO energy levels with increasing chain length, while absorption and emission data showed a bathochromic shift and increase in quantum efficiency. An extended conjugation length of n(ECL)=5 was derived.

Donor–π–Acceptor Polymer with Alternating Triarylborane and Triphenylamine Moieties

A luminescent main chain donor-π-acceptor-type polymer (4) was prepared via organometallic polycondensation reaction followed by post modification. With both electron-rich amine and electron-deficient borane moieties embedded in the main chain, 4 exhibits an interesting ambipolar character: it can be reduced and oxidized electrochemically at moderate potentials and shows a strong solvatochromic effect in the emission spectra. Complexation studies show that 4 selectively binds to fluoride and cyanide; quantitative titration with cyanide reveals a two-step binding process.

Lewis acidity enhancement of organoboranes via oxidation of appended ferrocene moieties

The Lewis acidity of boron in diboradiferrocene 1 is strongly enhanced through oxidation of the iron atoms as evident from examination of X-ray structural parameters of the mixed-valent cation 1(+)PF(6) and further confirmed from the strong complexation of MeCN to the dication in 2(2+)(I(3))(2).

A comparative study of base-free arylcopper reagents for the transfer of aryl groups to boron halides

Abstract A comparative study on the reactivity and selectivity of arylcopper species in reactions with boron halides was performed. Mesitylcopper reacts with BX 3 (X=Cl, Br) in toluene at low temperature under highly selective formation of the monosubstituted boranes MesBX 2 . The dimesitylboranes Mes 2 BX are gradually formed with a twofold excess of the organocopper reagent at elevated temperature. In contrast, pentafluorophenylcopper shows a tendency for formation of B(C 6 F 5 ) 3 in reactions with BX 3 irrespective of the stoichiometry used, suggesting a strong impact of electronic factors on the selectivity of the aryl transfer reaction. New procedures for the synthesis of the pentafluorophenylboron halides C 6 F 5 BX 2 (X=Cl: 57%; X=Br: 62%) and of tris(pentafluorophenyl)borane (80%) and related mixed-substituted triarylboranes from the base-free isolable pentafluorophenylcopper precursor have been developed.

Synthesis by free radical polymerization and properties of BN-polystyrene and BN-poly(vinylbiphenyl)

Free radical polymerization of B-vinyl- and B-styryl-functionalized azaborinine monomers gives well-defined hybrid polymers that were fully characterized by multinuclear NMR and GPC analysis; their solubility, thermal characteristics, and photophysical properties are dramatically different from those of the all-carbon polystyrene analogues.

Recent Advances in the Synthesis and Applications of Organoborane Polymers

Recent advances in the synthesis of organoborane polymers are reviewed in this chapter. The last decade has witnessed new approaches for the direct polymerization of functional borane monomers as well as the use of innovative polymer modification techniques. Powerful new methods that allow for positioning of functional borane moieties at well-defined positions in the polymer chain have also been developed. The resulting organoborane polymers have been investigated as luminescent and electro-active materials, electrolytes for batteries, supported Lewis acid catalysts, sensors for anions and biologically relevant molecules, building blocks of stimuli-responsive and dynamic (supramolecular) materials, and for biomedical applications.