Chemical synthesis of organoborane polymers and their applications is discussed. The past decade has seen a renewal of interest and development of main group organometallic chemistry.
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IJS, KILJ, NUK, PNG, UL, UM
The past decade has witnessed tremendous advances in the synthesis of polymers that contain elements from the main groups beyond those found in typical organic polymers. Unique properties that arise ...from dramatic differences in bonding and molecular geometry, electronic structure, and chemical reactivity, are exploited in diverse application fields. Herein we highlight recent advances in inorganic backbone polymers, discuss how Lewis acid/base functionalization of polymers results in unprecedented reactivity, and survey conjugated hybrids with unique electronic structures for sensor and device applications.
Polymers go main group! This Review shows how the incorporation of the full range of available main‐group elements into polymers leads to new functional hybrid materials with potential use in diverse application fields ranging from advanced elastomers, responsive gels, biodegradable materials, to organic electronics, imaging agents, sensors, and supported catalysts.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The functionalization of polymeric materials with Lewis acidic boron sites has led to exciting new opportunities in diverse areas, ranging from new polymeric catalysts to the preparation of highly ...luminescent materials and the design of efficient sensor systems for nucleophiles. Recent advances in the preparation of these Lewis acidic boron polymers, their coordination behavior, and some of their intriguing applications are reviewed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Classical Lewis pairs (LPs) between unhindered electron-poor Lewis acids (LAs) and electron-rich Lewis bases (LBs) present an overlooked motif with tremendous potential as dynamic cross-links in ...transient polymer networks (TPNs) for self-healing and stimuli-responsive applications. We demonstrate that simple and intuitive matching of weak/strong organoborane LA and amine LB pairs offers access to a large set of binding equilibrium constants, K eq, that span ∼6 orders and dissociation rate constants, k diss, that span ∼7 orders of magnitude. The implementation in polystyrene (PS)/polydimethylsiloxane (PDMS) blends results in dynamically cross-linked networks with bulk thermomechanical properties that are directly correlated with the strength and kinetic parameters for the LP interactions. The LP dynamic cross-link design is highly versatile and broadly applicable to different polymer architectures as demonstrated in the formation of reprocessable elastomers from Lewis base-decorated high molecular weight PDMS in combination with Lewis acid-decorated PS when reinforced with fumed silica as a filler.
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The extension of conjugated organoboranes from monomeric species to oligomers, macrocycles, and polymers offers access to a plethora of fascinating new materials. The p–π* conjugation between empty ...orbitals on boron and the conjugated linkers not only affects the electronic structure and optical properties, but also enables mutual interactions between electron‐deficient boron centers. The unique properties of these electron‐deficient π‐conjugated systems are exploited in highly luminescent materials, organic optoelectronic devices, and sensing applications.
The development of π‐extended organoboranes is systematically discussed from both theoretical and experimental perspectives. An analysis of the p–π* conjugation and of mutual interactions between electron‐deficient boron centers across π‐conjugated linkers allows for important structure–property relationships to be deduced. It is also illustrated how the unique properties of these boron‐containing π‐conjugated systems are exploited in the field of organic optical and optoelectronic device materials.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This perspective highlights recent progress on the design, synthesis and applications of thienylboranes as building blocks for new functional materials. Well-controlled synthetic protocols, such as ...boron-tin and boron-silicon exchange reactions, hydroboration of alkynyl groups, and electrophilic borylations provide opportunities to access thiophene-boranes that are chemically robust and display desirable photophysical properties, redox characteristics, and solid-state assembly behavior. Diverse protocols for further functionalization allow for facile integration into larger conjugated structures and even polymeric systems. Moreover, the strong Lewis acid character that is characteristic of trivalent boranes facilitates intra- and intermolecular Lewis acid-base interactions that can further enrich the chemical and electronic properties of thiophene-borane materials. Recent advances with respect to applications in sensing, organic electronics, and the development of molecular switches are also discussed.
Recent advances on the use of thienylborane chemistry for the development of new functional materials are highlighted.
Covering an exceptionally wide range of bond strengths, the dynamic nature and facile tunability of dative B−N bonds is highly attractive when it comes to the assembly of supramolecular polymers and ...materials. This Minireview offers an overview of advances in the development of functional materials where Lewis pairs (LPs) play a key role in their assembly and critically influence their properties. Specifically, we describe the reversible assembly of linear polymers with interesting optical, electronic and catalytic properties, discrete macrocycles and molecular cages that take up diverse guest molecules and undergo structural changes triggered by external stimuli, covalent organic frameworks (COFs) with intriguing interlocked structures that can embed and separate gases such as CO2 and acetylene, and soft polymer networks that serve as recyclable, self‐healing, and responsive thermosets, gels and elastomeric materials.
Boron‐nitrogen Lewis pairs (LPs) serve as versatile motifs that not only facilitate self‐assembly but also endow macromolecules with unique characteristics. The dynamic nature of the dative bonding is exploited in the generation of new macrocycles, molecular cages, 1D polymers, and 3D networks with interesting optical and electronic properties, host–guest characteristics, stimuli‐responsiveness, and shape‐shifting properties.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Two novel luminescent triarylborane polymeric Lewis acids and the corresponding molecular model compounds were prepared, studies on their photophysical properties performed, and applications as ...supported catalysts in Lewis acid-catalyzed hydrosilylation reactions explored. Variations of the substituents in the ortho-position of a phenylene linker between the Lewis acidic borane and the polystyrene framework lead to steric and electronic fine-tuning while retaining the high Lewis acidity of the boron center. The polymeric Lewis acids serve as effective catalysts in the hydrosilylation of aldehyde, ketone, and imine compounds and because of their distinct solubility characteristics are readily amenable to recycling. In addition, as a result of the twisted biphenyl donor−π-acceptor structure, both the styrene copolymers and model compounds display strong luminescence in solution and the solid state, encompassing prompt fluorescence and in the case of the chlorophenyl-linked derivative also longer-lived room temperature phosphorescence (RTP). Consistent with quantum-chemical calculations, the greater donor strength of the 2,6-dimethylphenyl in comparison to the 2-chlorophenyl linker leads to a red-shifted emission, while the chloro substituent leads to a larger gap between singlet and triplet excited states. In the solid state, distinctly different emission properties are observed for the polymers in comparison to the molecular compounds because of the site isolation of the chromophores embedded in the polymer matrix.
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B–N-fused dianthracenylpyrazine derivatives are synthesized to generate new low gap chromophores. Photophysical and electrochemical, crystal packing, and theoretical studies have been performed. Two ...energetically similar conformers are identified by density functional theory calculations, showing that the core unit adopts a curved saddle-like shape (x-isomer) or a zig-zag conformation (z-isomer). In the solid state, the z-isomer is prevalent according to an X-ray crystal structure of a C6F5-substituted derivative (4-Pf), but variable-temperature nuclear magnetic resonance studies suggest a dynamic behavior in solution. B–N fusion results in a large decrease of the HOMO–LUMO gap and dramatically lowers the LUMO energy compared to the all-carbon analogues. 4-Pf in particular shows significant absorbance at greater than 700 nm while being almost transparent throughout the visible region. After encapsulation in the biodegradable polymer DSPE-mPEG2000, 4-Pf nanoparticles (4-Pf-NPs) exhibit good water solubility, high photostability, and an excellent photothermal conversion efficiency of ∼41.8%. 4-Pf-NPs are evaluated both in vitro and in vivo as photothermal therapeutic agents. These results uncover B–N Lewis pair functionalization of PAHs as a promising strategy toward new NIR-absorbing materials for photothermal applications.
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Tridentate ligands that incorporate pyridyl rather than pyrazolyl groups are emerging as an attractive class of "scorpionate"-type ligands with enhanced electron donation, increased stability, and ...divergent geometry at the metal centre relative to tris(pyrazolyl)borates originally introduced by Trofimenko. Following our initial reports, the tris(pyridyl)borate (Tpyb) ligand architecture has been adopted by several research groups in pursuit of functional metal complexes that offer new opportunities in catalysis and materials science. While earlier work had been focused on symmetric octahedral complexes, ML
2
, which are advantageous as highly robust building blocks in materials sciences, recently introduced new ligand designs provide access to heteroleptic metal complexes with vacant sites that lend themselves to applications in catalysis. Signficant progress has also been made in the post-complexation functionalization of these ligands
via
electrophilic and nucleophilic substitution reactions at the boron centres, opening up new routes for integration of Tpyb complexes with diverse functional materials while also raising interesting mechanistic questions.
Recent progress in the development of tris(pyridyl)borate ligands and their complexes is discussed, and promising future directions are outlined.
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