Aluminum Complexes of N2O23- Formazanate Ligands Supported by Phosphine Oxide Donors

Advancements in boron difluoride formazanate dyes for biological imaging

In the past decade, boron difluoride formazanate dyes have gained considerable attention due to their redox activity, high absorption and emission intensities, chemical stability across a broad range of conditions, and the ease to fine-tune their optical and electronic characteristics. Over the past five years, boron difluoride formazanate dyes have demonstrated their extended emission wavelengths in the near-infrared region, suggesting their potential applications in the field of biological imaging. This review provides an overview of the evolution of boron difluoride formazanate dyes, encompassing the structural variations and corresponding optical properties, while also highlighting their current applications in biological imaging fields.

C─H Activation Enables the Construction of New Bis-Polyaryl Phenylpyridine Ruthenium Complexes: Conjugation and Rigidity Synergistic Effect for Advanced Electrochemiluminescence

The access to bench-stable organometallic compounds unfolds new chemical space for medicinal and material sciences. In particular, stable organoruthenium compounds with constitutional and stereoisomeric forms for subtle regulation of electrochemiluminescence are intriguing and challenging. Here, coordination of polycyclic aromatic hydrocarbons on (2-phenylpyridine)2(CO)2Ru complex allows access to bis-polyaryl phenylpyridine (BPP) Ruthenium complex through C─H activation strategy and coupling reactions for installation of the functionalities with steric and electronic purposes. The photoluminescence and electrochemiluminescence of BPP Ru complexes are affected by the actual polycyclic aromatic hydrocarbons inherent properties. The anthracene derivatized BPP Ru complex (BPP-Ant) shows the best ECL performance and reveals an enormous ECL quantum efficiency of 1.6-fold higher than the golden standard Ru(bpy)3 2+. The unprecedentedly high efficiency is due to the best compromise between the structural conjugation and molecular rigidity from BPP-Ant providing a providential energy gap that facilitated the feasibility of electron transfer and favored the radiative energy release by experimentally and DFT calculations. Moreover, PL and spooling ECL spectroscopies are used to track and link multiple emission peaks of BPP-Ant at 445, 645, and 845 nm to different emissive species. These discoveries will add a new member to the efficient ECL ruthenium complex family and bring more potentials.

Trimetallic Iridium-Nickel-Iridium Bis(formazanate) Assemblies

Formazans have attracted a lot of attention in coordination chemistry since the early 1940s because of their unique properties engendered by the nitrogen-rich conjugated backbone. Although many studies have been done using formazanates to chelate transition metals, research using formazanates as building blocks for polynuclear compounds and supramolecular chemistry remains rare. In this paper, we describe a synthetic strategy that uses a pyridyl-substituted bis(formazanato)nickel complex as a metalloligand to further assemble with two [Ir(C^N)₂]⁺ centers (C^N is the cyclometalating ligand). The trimetallic complexes represent a new binding mode for flexidentate pyridyl-substituted formazanates and a new structural class of polynuclear formazanate complexes. This work expands the chemistry of polynuclear formazanate complexes, for the first time pairing 3d and 5d metals in the same assembly. The redox chemistry of these trimetallic complexes, evaluated via cyclic voltammetry, is described. The compounds described in this work are luminescent, and studies of bis-cyclometalated iridium model complexes lacking the formazanate bridge confirm that the phosphorescence arises from the iridium center.

Redox noninnocence of formazanate ligand applied to catalytic formation of α-ketoamides

The formazan ligands have been investigated as redox noninnocent backbone for a long time. Despite its well-established behaviour as redox reservoir, demonstration of catalytic efficiency governed by redox noninnocence remains...

Spooling electrochemiluminescence spectroscopy: development, applications and beyond

One of the most widely used techniques to generate light through an efficient electron transfer is called electrochemiluminescence, or electrogenerated chemiluminescence (ECL). ECL mechanisms can be explored via 'spooling spectroscopy' in which individual ECL spectra showing emitted light are collected continuously during a potentiodynamic course. The obtained spectra are spooled together and plotted along the applied potential axis; because the potential sweep occurs at a defined rate, this axis is directly proportional to time. Any changes in the emission spectra can be correlated to the corresponding potentials and/or times, leading to a deeper understanding of the mechanism for light generation-information that can be used for efficiently maximizing ECL intensities. The formation of intermediates and excited states can also be tracked, which is crucial to interrogating and drawing electron transfer pathways (i.e., understanding the chemical reaction mechanism). Spooling spectroscopy is not limited to ECL; we also include instructions for the use of related methodologies, such as spooling photoluminescence spectroscopy during an electrolysis procedure, which can be easily set up. The total time required to complete the protocol is ~49 h, from making electrodes and an ECL cell, fabricating light-tight housing, to setting up instruments. Preparing the lab for an individual experiment (making an electrolyte solution of a targeted luminophore, cooling down the CCD camera, calibrating the spectrometer and surveying electrochemistry) takes ~1 h 15 min, and performing the spooling ECL spectroscopy experiment itself requires ~10 min.

Cationic Boron Formazanate Dyes*

Incorporation of cationic boron atoms into molecular frameworks is an established strategy for creating chemical species with unusual bonding and reactivity but is rarely thought of as a way of enhancing molecular optoelectronic properties. Using boron formazanate dyes as examples, we demonstrate that the wavelengths, intensities, and type of the first electronic transitions in BN heterocycles can be modulated by varying the charge, coordination number, and supporting ligands at the cationic boron atom. UV-vis absorption spectroscopy measurements and density-functional (DFT) calculations show that these modulations are caused by changes in the geometry and extent of π-conjugation of the boron formazanate ring. These findings suggest a new strategy for designing optoelectronic materials based on π-conjugated heterocycles containing boron and other main-group elements.

Synthesis and characterization of group 13 dichloride (M = Ga, In), dimethyl (M = Al) and cationic methyl aluminum complexes supported by monoanionic NNN-pincer ligands

A series of monoanionic NNN-pincer ligands effectively stabilize five-coordinate gallium and indium dichloride complexes, as well as neutral dimethyl aluminum species, and organometallic cations thereof.

Dinuclear Complexes of Flexidentate Pyridine-Substituted Formazanate Ligands

The utility of flexidentate pyridyl-substituted formazanate ligands for assembling dinuclear coordination complexes with iridium(III) and/or platinum(II) building blocks is demonstrated herein. The dinuclear complexes are prepared either via a stepwise strategy, adding one metal unit at a time, or via one-pot self-assembly. Eight of the new complexes, including both mononuclear precursors and dinuclear products, are structurally characterized by single-crystal X-ray diffraction and NMR spectroscopy, revealing several distinct binding modes of the formazanates. All complexes are characterized by UV/Vis absorption spectroscopy and cyclic voltammetry. The frontier orbitals are primarily localized on the formazanate ligand, and a characteristic, intense formazanate-centered π→π* absorption band is observed in the absorption spectra.

Cation effects on dynamics of ligand-benzylated formazanate boron and aluminium complexes

The dynamic processes present in ligand-benzylated formazanate boron and aluminium complexes are investigated using variable temperature NMR experiments and lineshape analyses. The observed difference in activation parameters for complexes containing either organic countercations (NBu4+) or alkali cations is rationalized on the basis of a different degree of ion-pairing in the ground state, and the data are in all cases consistent with a mechanism that involves pyramidal inversion at the nitrogens in the heterocyclic ring rather than homolytic N-C(benzyl) bond cleavage.

Azo-triazolide bis-cyclometalated Ir(iii) complexes via cyclization of 3-cyanodiarylformazanate ligands

In this work we describe the synthesis of sterically encumbered 1,5-diaryl-3-cyanoformazanate bis-cyclometalated iridium(iii) complexes, two of which undergo redox-neutral cyclization during the reaction to produce carbon-bound 2-aryl-4-arylazo-2H-1,2,3-triazolide ligands. This transformation offers a method for accessing 2-aryl-4-arylazo-2H-1,2,3-triazolide ligands, a heretofore unreported class of chelating ligands. One formazanate complex and both triazolide complexes are structurally characterized by single-crystal X-ray diffraction, with infrared spectroscopy being the primary bulk technique to distinguish the formazanate and triazolide structures. All complexes are further characterized by UV-Vis absorption spectroscopy and cyclic voltammetry, with the triazolide compounds having similar frontier orbital energies to the formazanate complexes but much less visible absorption.

Formazanate coordination compounds: synthesis, reactivity, and applications

Inorganic complexes of an emerging class of chelating N-donor ligands, formazanates, offer a unique combination of structurally tunable coordination modes, redox activity, and optoelectronic properties.

Altering the optoelectronic properties of boron difluoride formazanate dyes via conjugation with platinum(ii)-acetylides

The absorption, emission, and electrochemical properties of conjugates of boron difluoride formazanate dyes and Pt(ii)-acetylides are systematically studied.

Aluminum Complexes with Redox-Active Formazanate Ligand: Synthesis, Characterization, and Reduction Chemistry

The synthesis of aluminum complexes with redox-active formazanate ligands is described. Salt metathesis using AlCl₃ was shown to form a five-coordinate complex with two formazanate ligands, whereas organometallic aluminum starting materials yield tetrahedral mono(formazanate) aluminum compounds. The aluminum diphenyl derivative was successfully converted to the iodide complex (formazanate)AlI₂, and a comparison of spectroscopic/structural data for these new complexes is provided. Characterization by cyclic voltammetry is supplemented by chemical reduction to demonstrate that ligand-based redox reactions are accessible in these compounds. The possibility to obtain a formazanate aluminum(I) carbenoid species by two-electron reduction was examined by experimental and computational studies, which highlight the potential impact of the nitrogen-rich formazanate ligand on the electronic structure of compounds with this ligand.

The synthesis of a series of aluminum complexes with redox-active formazanate ligands is described and crystallographic, spectroscopic, and voltammetric characterization data are presented. The reduction chemistry of these newly synthesized complexes has been explored and the results are supported by a computational (DFT) study.

Structure and bonding in reduced boron and aluminium complexes with formazanate ligands

A comparison of structure and bonding in reduced formazanate B/Al complexes and their ligand-benzylated products is described. The kinetics of homolytic N–C(benzyl) bond cleavage in the latter compounds is studied.

Reactivity of Two-Electron-Reduced Boron Formazanate Compounds with Electrophiles: Facile N-H/N-C Bond Homolysis Due to the Formation of Stable Ligand Radicals

The reactivity of a boron complex with a redox-active formazanate ligand, LBPh₂ [L = PhNNC(p-tol)NNPh], was studied. Two-electron reduction of this main-group complex generates the stable, nucleophilic dianion [LBPh₂]^2–, which reacts with the electrophiles BnBr and H₂O to form products that derive from ligand benzylation and protonation, respectively. The resulting complexes are anionic boron analogues of leucoverdazyls. N–C and N–H bond homolysis of these compounds was studied by exchange NMR spectroscopy and kinetic experiments. The weak N–C and N–H bonds in these systems derive from the stability of the resulting borataverdazyl radical, in which the unpaired electron is delocalized over the four N atoms in the ligand backbone. We thus demonstrate the ability of this system to take up two electrons and an electrophile (E⁺ = Bn⁺, H⁺) in a process that takes place on the organic ligand. In addition, we show that the [2e^–/E⁺] stored on the ligand can be converted to E^• radicals, reactivity that has implications in energy storage applications such as hydrogen evolution.

A boron complex with a redox-active formazanate ligand in its two-electron-reduced state is shown to react with electrophiles (BnBr and H⁺). The resulting “borataleucoverdazyl” products have weak N−C and N−H bonds; homolytic cleavage reactions lead to stable ligand-based radicals. Thus, the accumulation of [2e⁻/E⁺] on the formazanate ligand and conversion to E^• radicals are demonstrated, and their potential relevance in energy-related electrocatalysis (e.g., proton reduction) is discussed.