(Co)Polymers Containing Boron Difluoride 3-Cyanoformazanate Complexes: Emission Enhancement via Random Copolymerization

Ring-opening metathesis polymerization was used to produce polymers bearing an asymmetrically substituted boron difluoride 3-cyanoformazanate complex. The polymers were found to retain many of the unique characteristics of molecular boron difluoride complexes of 3-cyanoformazanates, including intense light absorption at ca. 560 nm and reversible electrochemical reductions implicating the radical anion and dianion forms of the formazanate complexes in the repeating unit of the polymer backbone. The polymers were also found to be emissive, with emission maxima centred at ca. 665 nm. The monomer employed in this study had a fluorescence quantum yield of 30%, while homopolymers were weakly emissive and block copolymers were essentially non-emissive. The development of a monomer ‘dilution’ strategy, via random copolymerization, resulted in rejuvination of the emission at ca. 665 nm up to a maximum quantum yield of 24% when the mole fraction of the repeating units bearing boron difluoride 3-cyanoformazanate complexes (ƒBF2N) was 0.08

Boron Difluoride Formazanate Copolymers with 9,9-Di-n-hexylfluorene Prepared by Copper-Catalyzed Alkyne-Azide Cycloaddition Chemistry

The synthesis and characterization of copolymers based on boron difluoride formazanate (BF2L) and 9,9-di-n-hexylfluorene (hex2Fl) units are described. A series of model compounds [(BF2L)-(hex2Fl), (hex2Fl)-(BF2L)-(hex2Fl), and (BF2L)-(hex2Fl)-(BF2L)] were also studied in order to fully understand the spectroscopic properties of the title copolymer [(BF2L)-(hex2Fl)]n. The model compounds and copolymers, which were synthesized by copper catalyzed alkyne-azide cycloaddition chemistry, exhibited high molar absorptivities (25,700-54,900 M-1 cm-1), large Stokes shifts (123-143 nm, 3590-3880 cm-1), and tunable electrochemical behaviour (E°red1 ca. -0.75 V and E°red2 ca. -1.86 V vs. ferrocene/ferrocenium). The low-energy wavelength of maximum absorption and emission of the model compounds red-shifted relative to the BF2L repeating unit by ca. 30 nm per triazole ring formed, to maximum values of 557 nm and 700 nm in DMF, respectively. The low-energy absorption and emission properties of the copolymer were consistent with the model compound bearing two triazole rings [(hex2Fl)-(BF2L)-(hex2Fl)] and were not dependant on copolymer molecular weight. However, the title copolymers may show promise as a light-harvesting material based on their thin-film optical band gap of 1.67 eV

Aggregation-Induced Emission Enhancement in Boron Difluoride Complexes of 3-Cyanoformazanates

Boron difluoride (BF2) complexes of 3-cyanoformazanates exhibit aggregation-induced emission enhancement in THF-water mixtures due to their severely twisted N-aryl substituents which restrict intramolecular motion and π stacking upon aggregation

A Phosphine-Based Heterotrimetallic (M = Fe, Ru, W) Homo-polymer

An organometallic homopolymer containing three different metals per repeating unit was synthesized from an air- and moisture-stable secondary phosphine bearing ethylferrocene and ethylruthenocene groups. Hydrophosphination yielded a tertiary phosphine bearing an alcohol, which was then used to introduce a polymerizable styrene group via DCC coupling. Free-radical polymerization, followed by post-polymerization coordination to photogenerated W(CO)5 units yielded the title polymer, which showed thermal, spectroscopic, and electrochemical properties associated with each of the transition metals involved

Design, Synthesis, and Characterization of a Phosphine-based Heterotrimetallic (M = Fe, Ru, W) Homopolymer

An organometallic homopolymer containing three different metals per repeating unit was synthesized from an air- and moisture-stable secondary phosphine bearing ethylferrocene and ethylruthenocene groups. Hydrophosphination yielded a tertiary phosphine bearing an alcohol, which was then used to introduce a polymerizable styrene group via DCC coupling. Free-radical polymerization, followed by post-polymerization coordination to photogenerated W(CO)5 units yielded the title polymer, which showed thermal, spectroscopic, and electrochemical properties associated with each of the transition metals involved

Synthesis, Characterization, and Pre-Ceramic Properties of π-Conjugated Polymers Based on Ni(II) Complexes of Goedken’s Macrocycle

Nickel(II) complexes of Goedken’s macrocycle bearing alkyne substituents were copolymerized with 2,7-dibromo-9,9-dihexylfluorene, 2,5-dibromo-3-hexylthiophene, and 1,4-dibromo-2,5-bis(hexyloxy)benzene via microwave-induced Sonogashira cross-coupling reactions to produce copolymers 6F, 6T, and 6B. The spectroscopic and electrochemical properties of the copolymers were examined and compared to model compounds. Specifically, each polymer exhibited a nickel-based absorption centered at ca. 589 nm and two π → π* transitions between 272 and 387 nm. While the copolymers did not exhibit extended π conjugation, the nature of the organic spacer did affect the high energy transitions. Furthermore, each copolymer underwent two ligand-based one-electron oxidations at potentials of ca. 0.24 V and ca. 0.75 V relative to the ferrocene/ferrocenium redox couple. Post-polymerization functionalization of the alkyne group in 6F with Co2(CO)8 afforded a novel heterobimetallic copolymer that yielded amorphous nanomaterials containing Ni/Co when pyrolyzed at 800 °C for 3 h under an atmosphere of N2/H2 (95:5)

Formazanate coordination compounds:Synthesis, reactivity, and applications

Formazans (Ar1-NH-NCR3-NN-Ar5), a class of nitrogen-rich and highly colored compounds, have been known since the late 1800s and studied more closely since the early 1940s. Their intense color has led to their widespread use as dyes, especially in cell biology where they are most often used to quantitatively assess cell-viability. Despite structural similarities to well-known ligand classes such as β-diketiminates, the deprotonated form of formazans, formazanates, have received relatively little attention in the transition metal and main group coordination chemistry arenas. Formazanate ligands benefit from tunable properties via structural variation, rich optoelectronic properties owing to their highly delocalized π-systems, low-lying frontier orbitals that stabilize otherwise highly reactive species such as radicals, and redox activity and coordinative flexibility that may have significant implications in their future use in catalysis. Here, we review progress in the coordination chemistry of formazanate ligands over the past two decades, with emphasis on the reactivity and applications of the subsequent complexes

Metal-containing polymers bearing pendant nickel(II) complexes of Goedken\u27s macrocycle

The design, synthesis, and polymerization of a norbornene-based monomer bearing a nickel(II) complex of Goedken\u27s macrocycle (endo-13) and the characterization of the resulting polymer are described. Detailed studies of the ring-opening metathesis polymerization of endo-13 using the 3-bromopyridine adduct of Grubbs\u27 3rd generation catalyst revealed that the polymerization shares many characteristics associated with a living polymer, but deviated from ideal behavior when high degrees of polymerization were targeted. The installation of a 3-hexylphenyl substituent at the macrocyclic backbone allowed for the realization of soluble polymers (14) and shut down an oxidative dimerization pathway commonly associated with metal complexes of Goedken\u27s macrocycle. The cyclic voltammogram of the polymer 14 was comprised of two one-electron oxidation waves (0.21 V and 0.70 V relative to ferrocene/ferrocenium) associated with the stepwise oxidation of the macrocyclic ligand backbone and a one electron reduction wave associated with the reduction of nickel(II) to nickel(I) (-2.07 V). Solution and solid-state UV-vis absorption spectra recorded for polymer 14 revealed a strong p®p* absorption (lmax = 390 nm) and a ligand-to-metal charge transfer band (lmax = 590 nm) typical of nickel(II) complexes of Goedken\u27s macrocycle, and confirmed the absence of macrocycle-macrocycle interactions. This work has ultimately led to the development of a controlled polymerization route to a rare example of a side-chain nickel-containing polymer with potentially useful properties

Structurally Diverse Boron-Nitrogen Heterocycles from an N2O23− Formazanate Ligand

Five new compounds comprised of unprecedented boron-nitrogen heterocycles have been isolated from a single reaction of a potentially tetradentate N2O23− formazanate ligand with BF3­•OEt2 and NEt3. Optimized yields for each product were obtained through variation of experimental conditions and rationalized in terms of relative Gibbs free energies of the products as determined by electronic structure calculations. Chemical reduction of two of these compounds resulted in the formation of a stable anion, radical anion, and diradical dianion. Structural and electronic properties of this new family of redox-active heterocycles were characterized using UV-vis absorption spectroscopy, cyclic voltammetry and X-ray crystallography

An investigation into the hexagonal phases formed in high-concentration dispersions of well-defined cylindrical block copolymer micelles

<p>This paper presents a detailed analysis of the structure of the hexagonal phase of poly(ferrocenylsilane) (PFS)-based cylindrical micelles found at concentrations above ca. 5 wt. % in non-polar solvents such as decane. Small-angle X-ray scattering indicated that the hexagonal order is not long-range. In all samples, deviations in the lower order peak positions were observed with respect to those expected for a perfect hexagonal lattice, with the degree of deviation correlating with micelle length. Furthermore, analysis of the peak shapes and peak widths suggests that the phase possesses intermediate translational order similar. to the hexatic phase. The observed features can be reproduced by amending Hosemann’s paracrystal theory to include a distribution of lattice parameters to model well and poorly condensed regions. It is proposed that this distribution arises due to the bending and intertwining of individual micelles in a hexagonal lattice, resulting in a kinetically trapped phase that is initially neither perfectly hexagonal nor canonically hexatic but which anneals over time towards a perfect hexagonal lattice.</p