Heterocyclic and Open-Chain Carboranes via Transition-Metal-Free C–H Functionalization of Mono- and Diazine-N-oxides

Selective B(3)-H Activation Affording Multinuclear Ir(III) Complexes with (o-Carboranyl)dithioester Ligands

A method was developed to link two or three o-carborane moieties to form a series of carboranyl dithioester bridging ligands via in situ substitution of haloalkanes by tetraphenylphosphonium carboranyldithiocarboxylates. Based on these ligands, direct B-H activation without the assistance of Ag(I) and alkali was successfully achieved with half-sandwich Ir(III) substrate [Cp*IrCl2]2 to yield corresponding bimetallic or trimetallic complexes. Single crystal structure analyses of the B-H activated complexes and corresponding SnCl2-inserted derivatives confirm the selective B(3)-H activation in these complexes.

Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Synthesis of Carboranylated Dihydropyrrolo[1,2-a]quinoxalines and Dihydroindolo[1,2-a]quinoxalines by BF3·OEt2-Catalyzed Heterocyclization of C-Formyl-o-carboranes and Investigation of Their Oxidation Stability

A BF3·OEt2-catalyzed synthesis of carboranylated dihydropyrrolo[1,2-a]quinoxalines and dihydroindolo[1,2-a]quinoxalines in 30-99% yields is presented through the heterocyclization of various C-modified C-formyl-o-carboranes with 1-(2-aminophenyl)-pyrroles/indoles. A systematic comparative investigation of their oxidation stability in air confirmed that 4-carboranyl-4,5-dihydropyrrolo[1,2-a]quinoxaline had better stability than the 4-phenyl analogue. A cage-deboronation reaction for N-acetyl-substituted carboranylated dihydropyrrolo[1,2-a]quinoxaline produced the corresponding 7,8-nido-carborane cesium salt. A kinetic resolution was also realized to obtain an optically pure carboranylated N-heterocycle scaffold bearing a carborane cage carbon-bonded chiral stereocenter.

Color-tuning and manipulation of aggregation-induced emission efficiency of o-carborane–tetraphenylethylene dyads through substituted o-carboranes

Two new carborane-containing tetraphenylethylene derivatives (1 and 2) were designed and synthesized. Together with our previously published compounds (3–5), we studied structure–activity relationships in detail. Results showed that compounds 1...

Synthesis and Optoelectronic Properties of Cationic Iridium(III) Complexes with o-Carborane-Based 2-Phenyl Benzothiazole Ligands

A series of cationic cyclometalated iridium(III) complexes with o-carborane cage on the main ligand of 2-phenylbenzothiazole were synthesized. The prepared iridium complexes (C1-C6) were fully characterized by UV-vis, NMR, and FT-IR spectra. The exact molecular structure of complex C1 was further studied by single crystal X-ray diffraction analysis. The different substitution position of o-carborane on the 2-phenylbenzothiazole ring lead to obvious differences in the emission properties of the synthesized complexes. The o-carboranyl unit results in a bathochromic shift of 10 nm in the fluorescence emission spectrum of C2. In addition, the presence of an o-carborane fragment promoted the strong fluorescence intensity of C1 and C4, which can be used as a tool to effectively boost the intensity of fluorescence properties. The emission fluorescent behavior of iridium(III) complexes can be facilely tuned by structural variations in the main ligands of these materials.

Manganese(iii) acetate-mediated activation of C–H bonds of weak CH-acids; addition ofo-carborane, its derivatives, and some other CH-acids to [60]-fullerene

CH-acids includingo-carboranes add to C₆₀by a carbon atomviaoxidative-ion-transfer reactions mediated by Mn(OAc)₃.

Copper-catalyzed cross-dehydrogenative coupling between quinazoline-3-oxides and indoles

A novel and simple protocol for the synthesis of 4-(indole-3-yl)quinazolines via cross-dehydrogenative coupling of quinazoline-3-oxides and indoles under an air atmosphere has been developed.

Direct C-4 alkylation of quinazoline N-oxides with ethers via an oxidative cross-coupling reaction under metal-free conditions

A novel and efficient protocol for the direct C-4 alkylation of quinazoline-3-oxides via radical oxidative coupling between quinazoline 3-oxides and ethers in the presence of TBHP was developed. The reaction proceeded smoothly under metal-free conditions, which provided quinazoline-containing heterocyclic molecules in moderate to good yields.

Transition metal-free oxidative and deoxygenative C-H/C-Li cross-couplings of 2H-imidazole 1-oxides with carboranyl lithium as an efficient synthetic approach to azaheterocyclic carboranes

The direct C-H functionalization methodology has first been applied to perform transition metal-free C-H/C-Li cross-couplings of 2H-imidazole 1-oxides with carboranyllithium. This atom- and step-economical approach, based on one-pot reactions of nucleophilic substitution of hydrogen (SN H) in non-aromatic azaheterocycles, affords novel imidazolyl-modified carboranes of two types (N-oxides and their deoxygenative analogues), which are particularly of interest in the design of advanced materials.

Nucleophilic C–H functionalization of arenes: a new logic of organic synthesis

Direct metal-free C–H functionalization of arenes with nucleophiles is a new chapter in the chemistry of aromatics. Comprehensive studies on nucleophilic substitution of hydrogen in arenes (the SNH reactions), including mechanisms, intermediates, mathematic and electrochemical modeling, kinetics, electron-transfer, etc. have shown that this is not the hydride ion, but C–H proton is departed, and this process is facilitated by the presence of an appropriate oxidant or an auxiliary group. The SNH reactions, as a part of the general C–H functionalization concept, change the logic of organic synthesis. They open new opportunities, avoiding incorporation of good leaving groups or other auxiliaries in an aromatic ring, as a prefunctionalization step, thus providing a better correspondence to the principles of green chemistry.