Cyclic Ruthenium(II)-Halocarbon Complexes Derived from Ru(II)-Induced Cyclization of Homopropargylic Halopyridines: Mechanism, Bonding and Reactivity.

The activation of various homopropargylic pyridines by cis-[Ru/Os(dppm)Cl] (dppm=1,1-bis(diphenylphosphino)methane) has previously been shown to generate a diverse array of metallacycles and metalated heterocyclic complexes. However, a minor structural modification of introducing a halide onto the pyridyl group of the alkyne substrate resulted in the formation of unprecedented Ru(II)/Os(II)-haloquinolizine complexes. These complexes display (1) κ(X,C)-haloquinolizine chelates arising from the cycloisomerization of HC≡CC(OH)(CH(6-X-2-py))(Ph) on [Ru/Os(dppm)] moieties via a vinylidene pathway, (2) five-membered Ru/Os-X-C-N-C rings (X=F, Cl, Br) ortho- and peri-fused to quinolizinium skeletons, and (3) uncommon M-X-R bonding interactions that are atypical in coordination complexes.

Controlling Chemoselectivity in Ruthenium(II)-Induced Cyclization of Aniline-Functionalized Alkynes.

The cyclization of heteroatom-functionalized alkynes induced by d-transition-metal centers has traditionally been associated with the vinylidene pathway. However, recent evidence suggests that d-transition-metal centers can also activate alkynes through non-vinylidene pathways. In this study, we conducted a comprehensive experimental and theoretical investigation into the reactions between the Ru(II) complex [Ru([9]aneS3)(bpy)(OH)] and 2-alkynylanilines.

Exploiting the Potential of Iridium(III) -Nitrone Complexes as Phosphorogenic Bifunctional Reagents for Phototheranostics.

Cross-linking strategies have found wide applications in chemical biology, enabling the labeling of biomolecules and monitoring of protein-protein interactions. Nitrone exhibits remarkable versatility and applicability in bioorthogonal labeling due to its high reactivity with strained alkynes via the strain-promoted alkyne-nitrone cycloaddition (SPANC) reaction. In this work, four cyclometalated iridium(III) polypyridine complexes functionalized with two nitrone units were designed as novel phosphorogenic bioorthogonal reagents for bioimaging and phototherapeutics.

Tetradentate Pt(II) Complexes Based on Xylenylamino Linked Dual Pyrazolate Chelates for Organic Light Emitting Diodes.

In this work, we report the syntheses of three Pt(II) emitters, namely, Pt4N1, Pt4N2, and Pt4N3, to which their tetradentate chelates were assembled by linking two pyrazolate chelates with a single xylenylamino entity. Functionalization of Pt4N1 was achieved upon the addition of electronegative CF substituent on pyridinyl groups and switching to more electron-deficient pyrazinyl groups in giving Pt4N2 and Pt4N3, respectively. The vertically arranged xylenylamino entity has effectively suppressed the inter-molecular π-π stacking and Pt⋅⋅⋅Pt interaction, as shown by the single crystal X-ray structural analyses.

Reactivity of a Hexaaryldiboron(6) Dianion as Boryl Radical Anions.

Our study unveils a novel approach to accessing boryl radicals through the spontaneous homolytic cleavage of B-B bonds. We synthesized a hexaaryl-substituted diboron(6) dianion, , via the reductive B-B coupling of 9-borafluorene. Intriguingly, compound exhibits the ability to undergo homolytic B-B bond cleavage, leading to the formation of boryl radical anions, as confirmed by EPR studies, in the presence of the 2.

Ir(III) Metal Emitters with Cyano-Modified Imidazo[4,5-b]pyridin-2-ylidene Chelates for Deep-Blue Organic Light-Emitting Diodes.

Ir(III) carbene complexes have been explored as one of the best blue phosphors for their high performance. Herein, the authors designed and synthesized a series of blue-emitting Ir(III) phosphors (f-ct9a-c), featuring fac-coordinated cyano-imidazo[4,5-b]pyridin-2-ylidene cyclometalates. These Ir(III) complexes exhibit true-blue emission with a peak maximum spanning 448-467 nm, with high photoluminescence quantum yields of 81-88% recorded in degassed toluene.

Reduction of Li within a borate anion.

Group 1 elements exhibit the lowest electronegativity values in the Periodic Table. The chemical reduction of Group 1 metal cations M to M(0) is extremely challenging. Common tetraaryl borates demonstrate limited redox properties and are prone to decomposition upon oxidation.

Bis-tridentate Ir(III) Phosphors and Blue Hyperphosphorescence with Suppressed Efficiency Roll-Off at High Brightness.

Narrowband blue emitters are indispensable in achieving ultrahigh-definition OLED displays that satisfy the stringent BT 2020 standard. Hereby, a series of bis-tridentate Ir(III) complexes bearing electron-deficient imidazo[4,5-]pyridin-2-ylidene carbene coordination fragments and 2,6-diaryloxy pyridine ancillary groups were designed and synthesized. They exhibited deep blue emission with quantum yields of up to 89% and a radiative lifetime of 0.

Electroluminescence and hyperphosphorescence from stable blue Ir(III) carbene complexes with suppressed efficiency roll-off.

Efficient Förster energy transfer from a phosphorescent sensitizer to a thermally activated delayed fluorescent terminal emitter constitutes a potential solution for achieving superb blue emissive organic light-emitting diodes, which are urgently needed for high-performance displays. Herein, we report the design of four Ir(III) metal complexes, f-ct1a ‒ d, that exhibit efficient true-blue emissions and fast radiative decay lifetimes. More importantly, they also undergo facile isomerization in the presence of catalysts (sodium acetate and p-toluenesulfonic acid) at elevated temperature and, hence, allow for the mass production of either emitter without decomposition.

Blue Electrophosphorescence from Iridium(III) Phosphors Bearing Asymmetric Di-N-aryl 6-(trifluoromethyl)-2H-imidazo[4,5-b]pyridin-2-ylidene Chelates.

Efficient blue phosphors remain a formidable challenge for organic light-emitting diodes (OLEDs). To circumvent this obstacle, a series of Ir(III)-based carbene complexes bearing asymmetric di-N-aryl 6-(trifluoromethyl)-2H-imidazo[4,5-b]pyridin-2-ylidene chelates, namely, f-ct6a‒c, are synthesized, and their structures and photophysical properties are comprehensively investigated. Moreover, these emitters can undergo interconversion in refluxing 1,2,4-trichlorobenzene, catalyzed by a mixture of sodium acetate (NaOAc) and p-toluenesulfonic acid monohydrate (TsOH·HO) without decomposition.

Cyclization, Decyclization, and Metallacyclization of Pyridine-Substituted Homopropargylic Alcohols on Ruthenium(II) and Osmium(II) Centers.

Systematic investigations on the reactions between cis-[M(dppm) Cl ] (M=Ru/Os; dppm=1,1-bis(diphenylphosphino)methane) and pyridine/quinoline substituted homopropargylic alcohols uncovered the diverse Ru(II)/Os(II)-induced alkyne activation pathways. The alkynes underwent cyclization on M via a "non-vinylidene" pathway at lower temperatures, resulting in alkenyl intermediates which might further metallacyclize to give metallapyrroloindolizines. Conversely, reactions at higher temperatures induced alkyne cyclization on M via a "vinylidene" pathway, affording cyclic oxacarbene complexes.

Structure and Reactivity of a Seven-Coordinate Ruthenium Iodosylbenzene Complex.

Seven-coordinate (CN7) ruthenium-oxo species have attracted much attention as highly reactive intermediates in both organic and water oxidation. Apart from metal-oxo, other metal-oxidant adducts, such as metal-iodosylarenes, have also recently emerged as active oxidants. We reported herein the first example of a CN7 Ru-iodosylbenzene complex, [Ru(bdpm)(pic)(O)I(Cl)Ph] (Hbdpm = [2,2'-bipyridine]-6,6'-diylbis(diphenylmethanol); pic = 4-picoline).

Engineering of Cyano Functionalized Benzo[]imidazol-2-ylidene Ir(III) Phosphors for Blue Organic Light-Emitting Diodes.

In this study, we designed and synthesized three series of blue emitting homoleptic iridium(III) phosphors bearing 4-cyano-3-methyl-1-phenyl-6-(trifluoromethyl)-benzo[]imidazol-2-ylidene (mfcp), 5-cyano-1-methyl-3-phenyl-6-(trifluoromethyl)-benzo[]imidazol-2-ylidene (ofcp), and 1-(3-(-butyl)phenyl)-6-cyano-3-methyl-4-(trifluoromethyl)-benzo[]imidazol-2-ylidene (5-mfcp) cyclometalates, respectively. These iridium complexes exhibit intense phosphorescence in the high energy region of 435-513 nm in the solution state at RT, to which the relatively large T → S transition dipole moment is beneficial for serving as a pure emitter and an energy donor to the multiresonance thermally activated delayed fluorescence (MR-TADF) terminal emitters via Förster resonance energy transfer (FRET). The resulting OLEDs achieved true blue, narrow bandwidth EL with a max EQE of 16-19% and great suppression of efficiency roll-off with ν-DABNA and -DABNA.

Visible Light-Induced Oxidation of Alcohols by a Luminescent Osmium(VI) Nitrido Complex: Evidence for the Generation of PhIO as a Highly Active Oxidant in the Presence of PhIO.

Although alcohols are readily oxidized by a variety of oxidants, their oxidation by metal nitrido complexes is yet to be studied. We report herein visible-light-induced oxidation of primary and secondary alcohols to carbonyl compounds by a strongly luminescent osmium(VI) nitrido complex (). The proposed mechanism involves initial rate-limiting hydrogen-atom transfer (HAT) from the α-carbon of the alcohol to .

Multitargeted Platinum(IV) Anticancer Complexes Bearing Pyridinyl Ligands as Axial Leaving Groups.

Although multitargeted Pt anticancer prodrugs have shown significant activities in reducing drug resistance, the types of bioactive ligands and drugs that can be conjugated to the Pt center remain limited to O-donors. Herein, we report the synthesis of Pt complexes bearing axial pyridines via ligand exchange reactions. Unexpectedly, the axial pyridines are quickly released after reduction, indicating their potential to be utilized as axial leaving groups.

Ring Nitrogenation of Aromatic Amines by the Excited State of an Osmium(VI) Nitrido Complex.

The reactivity of electrophilic Os and Ru nitrides toward various aliphatic and aromatic amines have been previously reported; these reactions all go through an initial nucleophilic addition of the amine nitrogen to M≡N (M = Os, Ru) to generate a M hydrazido species. Herein, we report that the excited state of a luminescent osmium(VI) nitrido complex, [Os(N)()(CN)] (, = 2-(2-hydroxy-5-nitrophenyl)benzoxazole), undergoes unprecedented ring nitrogenation of aromatic amines. Visible-light irradiation of generates , which predominantly attacks the aromatic ring of 2,6-dimethylaniline (MePhNH) to give an Os(II) benzoquinone diimine compound (PPh)[Os()(CN)(-NH═MePh═NH)] [] in 60% yield, while nucleophilic addition of the amine N to also occurs to give the osmium(II) diazonium compound (PPh)[Os()(CN)(N = N-MePh)] [] as a minor product (10% yield).

Cooperativity in Shape-Persistent Bis-(Zn-salphen) Catalysts for Efficient Cyclic Carbonate Synthesis under Mild Conditions.

A series of conformationally rigid (Zn-salphen) complexes with a planar bridging component (xanthene or dibenzofuran) are described. Conformational changes for these assemblies are essentially limited to the axial rotation of the Zn-salphen moieties; however, such geometric constraints crucially permit the subtle tuning of the intermetallic separation and geometry to potentially enhance catalytic activity (and cooperative effects). The complexes have been investigated as catalysts in conjunction with BuNI for the coupling of CO with epoxides.

Oxidative C-O bond cleavage of dihydroxybenzenes and conversion of coordinated cyanide to carbon monoxide using a luminescent Os(VI) cyanonitrido complex.

The photoreactions of a luminescent osmium(VI) nitrido complex, [Os(N)(L)(CN)] (OsN, HL = 2-(2-hydroxy-5-nitrophenyl)benzoxazole), with catechol (HCat) and hydroquinone (HQ) lead to the cleavage of strong C-OH bonds ( 120 kcal mol) of the dihydroxybenzenes with concomitant conversion of the coordinated cyanide to carbon monoxide.

Regioselective Syntheses of Imidazo[4,5-]pyrazin-2-ylidene-Based Chelates and Blue Emissive Iridium(III) Phosphors for Solution-Processed OLEDs.

Six homoleptic Ir(III) complexes bearing imidazo[4,5-]pyrazin-2-ylidene chelates were successfully designed and synthesized. Narrowband blue emission (λ = 466-485 nm) and broadened green emission (λ = 518-532 nm) in degassed toluene solution with high photoluminescent quantum yields in the range of 75-81 and 45-48% were observed for , , and as well as , , and , respectively. In addition, the -butylphenyl cyclometalate is more electron donating than -phenyl cyclometalate and, hence, all -butylphenyl-substituted derivatives, that is, and and and , give more red-shifted emission in comparison to that of and .

Structure and Reactivity of One- and Two-Electron Oxidized Manganese(V) Nitrido Complexes Bearing a Bulky Corrole Ligand.

As a strategy to design stable but highly reactive metal nitrido species, we have synthesized a manganese(V) nitrido complex bearing a bulky corrole ligand, [Mn(N)(TTPPC)] (, TTPPC is the trianion of 5,10,15-Tris(2,4,6-triphenylphenyl)corrole). Complex is readily oxidized by 1 equiv of CpFe to give the neutral complex , which can be further oxidized by 1 equiv of [(-Br-CH)N][B(CF)] to afford the cationic complex . All three complexes are stable in the solid state and in CHCl solution, and their molecular structures have been determined by X-ray crystallography.

Facile C-N bond cleavage of primary aliphatic amines by (salen)ruthenium(VI) nitrido complexes.

We report the first example of oxidative cleavage of the strong C-N bonds of primary amines by a ruthenium(VI) nitrido complex. The driving force for this very fast C-N cleavage reaction comes from the formation of stable NN after the initial coupling of the amine N and the nitrido ligand.

Ruthenafuran Complexes Supported by the Bipyridine-Bis(diphenylphosphino)methane Ligand Set: Synthesis and Cytotoxicity Studies.

Mononuclear and dinuclear Ru(II) complexes -[Ru(κ-dppm)(bpy)Cl] (), -[Ru(κ-dppe)(bpy)Cl] () and [Ru(bpy)(μ-dpam)(μ-Cl)](Cl) ([](Cl)) were prepared from the reactions between (Cl), (S)-[Ru(bpy)(dmso-)Cl] and diphosphine/diarsine ligands (bpy = 2,2'-bipyridine; dppm = 1,1-bis(diphenylphosphino)methane; dppe = 1,2-bis(diphenylphosphino)ethane; dpam = 1,1-bis(diphenylarsino)methane). While methoxy-substituted ruthenafuran [Ru(bpy)(κ-dppe)(C^O)] ([]; C^O = anionic bidentate [(OMe)CHC(Ph)] chelate) was obtained as the only product in the reaction between and phenyl ynone HC≡C(C=O)Ph in MeOH, replacing with led to the formation of both methoxy-substituted ruthenafuran [Ru(bpy)(κ-dppm)(C^O)] ([]) and phosphonium-ring-fused bicyclic ruthenafuran [Ru(bpy)(P^C^O)Cl] ([]; P^C^O = neutral tridentate [(Ph)CHP(Ph)CHC(Ph)] chelate). All of these aforementioned metallafuran complexes were derived from Ru(II)-vinylidene intermediates.

Stepwise Access of Emissive Ir(III) Complexes Bearing a Multi-Dentate Heteroaromatic Chelate: Fundamentals and Applications.

Three multi-dentate coordinated chelates LH ( = 1, 2, and 3), comprising a linked 1-(pyridin-2-yl)ethylbenzene and one pyrazolyl pyridine unit and showing either tridentate or tetradentate coordination modes, are successfully designed and synthesized. Dinuclear Ir(III) complexes [Ir(κ-L)(μ-Cl)] bearing tetradentate coordinated κ-L chelate (, = 1; , = 2; , = 3) were next obtained en route from the respective intermediate [Ir(κ-LH)Cl(μ-Cl)] bearing the tridentate coordinated κ-LH chelate (, = 1; , = 2; , = 3). Next, mononuclear Ir(III) complexes Ir(-L)(thd) (, = 1; , = 2; , = 3) with the tetradentate chelate were obtained upon treatment of with 2,2,6,6-tetramethyl-3,5-heptanedione (thd)H in the presence of KCO.

Visible light-induced oxidative -dealkylation of alkylamines by a luminescent osmium(vi) nitrido complex.

-Dealkylation of amines by metal oxo intermediates (M[double bond, length as m-dash]O) is related to drug detoxification and DNA repair in biological systems. In this study, we report the first example of -dealkylation of various alkylamines by a luminescent osmium(vi) nitrido complex induced by visible light.