Bulky Aryl Research Articles

Characterization of Iminobismuthanes and Catalytic Reduction of Organic Azides via Bi(I)/Bi(III) Redox Cycling

AbstractWe report the stoichiometric and catalytic reactivity of organobismuth(I) complexes with organic azides. Treatment of N,C,N‐pincer bismuthinidenes with organic azides (acyl, sulfonyl, and bulky aryl) results in monomeric iminobismuthanes which can be structurally characterized —including the formal Bi=N double bond— by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction. Building upon the stoichiometric reactivity of the monomeric iminobismuthanes, catalytic reduction of a broad range of organic azides is developed. DFT calculations of the catalytic reaction pathway support the redox nature of the overall process.

Characterization of Iminobismuthanes and Catalytic Reduction of Organic Azides via Bi(I)/Bi(III) Redox Cycling.

We report the stoichiometric and catalytic reactivity of organobismuth(I) complexes with organic azides. Treatment of N,C,N-pincer bismuthinidenes with organic azides (acyl, sulfonyl, and bulky aryl) results in isolable monomeric iminobismuthanes which can be structurally characterized-including the formal Bi=N double bond-by multinuclear NMR spectroscopy and single-crystal X-ray diffraction. Building upon the stoichiometric reactivity of the monomeric iminobismuthanes, catalytic reduction of a broad range of organic azides is developed. DFT calculations of the catalytic reaction pathway support the redox nature of the overall process.

Synthesis, Structure, Spectral, Redox, and Theoretical Studies of Sterically Crowded Decaaryl Triphyrin(2.1.1)s.

First examples of sterically crowded β- and meso-arylated decaaryl triphyrin(2.1.1)s were synthesized by reacting β-hexabromo meso-tetraaryl triphyrin(2.1.1) with five different aryl boronic acids in THF/toluene/H2O (1 : 1 : 1) in the presence of catalytic amount of Pd(PPh3)4/Na2CO3 at 80 °C for 12-24 h. The X-ray structure obtained for one of the decaaryl triphyrin(2.1.1)s revealed that the macrocycle exhibited saddle type of distortion due to steric crowding by bulky aryl substituents introduced at the six β-carbons of meso-tetraaryl triphyrin(2.1.1) unlike almost planar structure observed for β-unsubstituted meso-tetraaryl triphyrin(2.1.1). The absorption bands of decaaryl triphyrin(2.1.1)s were broadened and bathochromically shifted compared to meso-tetraaryl triphyrin(2.1.1) and the redox potentials were dependent on the kind of aryl substituents present at the β-pyrrole carbons in decaaryl triphyrin(2.1.1)s. DFT and TD-DFT studies helped in understanding the alteration in the structure, spectral, and redox properties in decaaryl triphyrin(2.1.1)s compared to meso-tetraaryl triphyrin(2.1.1).

Carbodiphosphorane-Activated Distibene and Dibismuthene Dications.

Low-valent antimony and bismuth have emerged as novel platforms for achieving reversible small-molecule activation at main-group metals. Although various examples of oxidative addition reactions at monomeric Sb(I) and Bi(I) have been reported, the chemistry of the heavy group 15 Sb(I)═Sb(I)/Bi(I)═Bi(I) double bonds toward small molecules remains largely unexplored. In this study, we present a straightforward synthesis of distibene and dibismuthene dications coordinated with a neutral carbodiphosphorane (CDP) ligand. The nonbonding interactions between the occupied p-orbital at the CDP ligand and the π-bonding orbital of the Sb═Sb/Bi═Bi bonds yield compounds with exceptionally small HOMO-LUMO gaps. In addition, the reduction of steric hindrance compared to known neutral derivatives stabilized with bulky aryl groups allows for better accessibility of the double bonds. This high reactivity is demonstrated in the oxidative addition of distibene to diphenyldisulfide as well as in [2+2] cycloadditions to alkynes. Additionally, the Sb═Sb bond reversibly adds to 2,3-dimethylbutadiene in a [4+2] cycloaddition reaction.

Synthesis of a stable crystalline nitrene.

Nitrenes are a highly reactive, yet fundamental, compound class. They possess a monovalent nitrogen atom and usually a short life span, typically in the nanosecond range. Here, we report on the synthesis of a stable nitrene by photolysis of the arylazide MSFluindN3 (1), which gave rise to the quantitative formation of the arylnitrene MSFluindN (2) (MSFluind is dispiro[fluorene-9,3'-(1',1',7',7'-tetramethyl-s-hydrindacen-4'-yl)-5',9''-fluorene]) that remains unchanged for at least 3 days when stored under argon atmosphere at room temperature. The extraordinary life span permitted the full characterization of 2 by single-crystal x-ray crystallography, electron paramagnetic resonance spectroscopy, and superconducting quantum interference device magnetometry, which supported a triplet ground state. Theoretical simulations suggest that in addition to the kinetic stabilization conferred by the bulky MSFluind aryl substituent, electron delocalization across the central aromatic ring contributes to the electron stabilization of 2.

Bis‐Ortho‐Donor‐Modification of Boracyclic π‐Electron Systems beyond Steric Protection to Produce Thermally Activated Delayed Fluorescence Materials

AbstractPolycyclic π‐conjugated compounds that contain tricoordinate boron atoms at their periphery represent an attractive class of materials with electron‐accepting character. Their molecular design generally requires the introduction of a bulky aryl group onto the boron atom, where it provides predominantly kinetic stabilization. The addition of extra functionality to the aryl group on the boron atom can be expected to further expand the potential utility of this class of materials. Herein, we report the synthesis of a series of boracyclic π‐conjugated molecules with firm ortho B⋅⋅⋅N nonbonding interactions by introducing N‐containing electron‐donors at the ortho‐positions of the aryl group on the boron atom. X‐ray crystallographic analysis revealed that the combination of a planar boracyclic π‐skeleton with only sp2 carbons and a strong electron‐donating phenothiazine moiety results in a particularly short B⋅⋅⋅N distance. Theoretical study provided insights into the inherent nature of the B⋅⋅⋅N interaction. Owing to their donor–acceptor (D−A) structures, these molecules exhibit substantially red‐shifted fluorescence in solution, albeit that the fluorescence quantum yields (ΦF) are low. In contrast, when incorporated into films, these compounds exhibit thermally activated delayed fluorescence (TADF) with improved ΦF values. Organic light‐emitting diodes (OLEDs) fabricated using the ortho‐donor‐substituted derivatives exhibit orange‐red electroluminescence.

Bis-Ortho-Donor-Modification of Boracyclic π-Electron Systems beyond Steric Protection to Produce Thermally Activated Delayed Fluorescence Materials.

Polycyclic π-conjugated compounds that contain tricoordinate boron atoms at their periphery represent an attractive class of materials with electron-accepting character. Their molecular design generally requires the introduction of a bulky aryl group onto the boron atom, where it provides predominantly kinetic stabilization. The addition of extra functionality to the aryl group on the boron atom can be expected to further expand the potential utility of this class of materials. Herein, we report the synthesis of a series of boracyclic π-conjugated molecules with firm ortho B⋅⋅⋅N nonbonding interactions by introducing N-containing electron-donors at the ortho-positions of the aryl group on the boron atom. X-ray crystallographic analysis revealed that the combination of a planar boracyclic π-skeleton with only sp2 carbons and a strong electron-donating phenothiazine moiety results in a particularly short B⋅⋅⋅N distance. Theoretical study provided insights into the inherent nature of the B⋅⋅⋅N interaction. Owing to their donor-acceptor (D-A) structures, these molecules exhibit substantially red-shifted fluorescence in solution, albeit that the fluorescence quantum yields (ΦF) are low. In contrast, when incorporated into films, these compounds exhibit thermally activated delayed fluorescence (TADF) with improved ΦF values. Organic light-emitting diodes (OLEDs) fabricated using the ortho-donor-substituted derivatives exhibit orange-red electroluminescence.

Hydrindacene‐Based Zinc Aryl Thiolate and Aryl Selenolate Zn(EMSFluind)2 (E=S, Se)

AbstractThe bulky aryl thiol, MSFluindSH (1S), and aryl selenol, MSFluindSeH (1Se), possessing a tetramethyl‐s‐hydrindacen‐4’‐yl‐(Rind)‐based substituent containing two fluorenyl groups in 9 and 9’‐positions, were prepared (MSFluind=dispiro[fluorene‐9,3’‐(1’,1’,7’,7’‐tetramethyl‐s‐hydrindacene‐4’‐yl)‐5’,9’’‐fluorene]). The reaction of 1S and 1Se with Et2Zn provided a monomeric zinc aryl thiolate, Zn(SMSFluind)2 (2S), and zinc aryl selenolate, Zn(SeMSFluind)2 (2Se), with essentially two‐coordinate zinc atoms.

N-Heterocyclic germylenes supported by bulky dianionic N,N-chelating ligands

In this contribution, three novel diamine pro-ligands, incorporating sterically bulky aryl and aliphatic N-substituents, have been developed; viz. (NCNTCHP)H2 (NCNTCHP = {(TCHP)NCH2}2CH2, TCHP = 2,4,6-tricyclohexylphenyl), (NONTCHP)H2 (NONTCHP = {(TCHP)NSiMe2}2O), and (NONAd)H2 (NONAd = {(Ad)NSiMe2}2O; Ad = 1-adamantyl). Through salt metathesis or transamination synthetic approaches, the N-heterocyclic germylenes, [:Ge(NCNTCHP)], [:Ge(NONTCHP)], and [:Ge(NONAd)], have been prepared and crystallographically characterized. The electronic structure of each germylene was studied by DFT calculations. The steric profile of the germanium-bound ligands was also assessed using computational models, and the results compared to those for structurally similar compounds. Significant steric crowding of the germanium centre (>70 % ligand coverage) was observed for [:Ge(NCNTCHP)] and [:Ge(NONTCHP)], while [:Ge(NONAd)] exhibited substantially less steric saturation at the metal centre (∼62 % ligand coverage). Through these studies, we have shown the potential suitably of the developed ligands to stabilise other low-valent main-group species.

Increased solar-driven chemical transformations through surface-induced benzoperylene aggregation in dye-sensitized photoanodes

The impact of benzo[ghi]perylenetriimide (BPTI) dye aggregation on the performance of photoelectrochemical devices was explored, through imide-substitution with either alkyl (BPTI-A, 2-ethylpropyl) or bulky aryl (BPTI-B, 2,6-diisopropylphenyl) moieties, to, respectively, enable or suppress aggregation. While both dyes demonstrated similar monomeric optoelectronic properties in solution, adsorption onto mesoporous SnO2 revealed different behavior, with BPTI-A forming aggregates via π-stacking and BPTI-B demonstrating reduced aggregation in the solid state. BPTI photoanodes were tested in dye-sensitized solar cells (DSSCs) before application to dye-sensitized photoelectrochemical cells (DSPECs) for Br2 production (a strong oxidant) coupled to H2 generation (a solar fuel). BPTI-A demonstrated a twofold higher dye loading of the SnO2 surface than BPTI-B, resulting in a fivefold enhancement to both photocurrent and Br2 production. The enhanced output of the photoelectrochemical systems (with respect to dye loading) was attributed to both J- and H- aggregation phenomena in BPTI-A photoanodes that lead to improved light harvesting. Our investigation provides a strategy to exploit self-assembly via aggregation to improve molecular light-harvesting and charge separation properties that can be directly applied to dye-sensitized photoelectrochemical devices.Graphical Increased Solar-Driven Chemical Transformations through Surface-Induced Benzoperylene Aggregation in Dye-Sensitized Photoanodes. Benzo[ghi]perylenetriimide (BPTI) dyes are investigated to reveal the effect of aggregation by π-stacking on photovoltaic parameters in dye-sensitized devices. Photoanodes with aggregating BPTIs show both J- and H- aggregation phenomena leading to enlarged visible light absorbance and increased electron injection. The use of aggregating BPTI outperforms a non-aggregation BPTI with fivefold in terms of photocurrent and product generation.

Nucleophilic Addition of Bulky Aryl Substituents to Pentacene‐6,13‐quinone

AbstractWe investigate the introduction of bulky aryl substituents of the biphenyl, terphenyl, and quaterphenyl type at the 6,13 and 5,7,12,14 positions of the pentacene scaffold by reaction of the corresponding quinones with lithium organic reagents. The 1,1′‐biphenyl‐2‐yl substituent could be installed at the 5,7,12,14‐positions and regioselectively either at 6,13 or at the 5,13 positions. The unsymmetrical substitution motif results from concomitant 1,2 and 1,4‐addition to 6,13‐pentacenequinone. A one‐pot protocol leads to isomeric symmetric 6,13‐disubstituted pentacenes and allows installation of two 5′‐phenyl‐[1,1′:3′,1′′‐terphenyl]‐2‐yl substituents. The four new pentacenes differ in crystal packing and photochemical stability.

Synthesis of 1‐Adamantylaminogermylene and Its Chalcogenation Reactions

AbstractThe synthesis, isolation, and characterization of 1‐adamantylaminogermylene 1 have been achieved utilizing kinetic stabilization with a bulky aryl group on the germanium atom. Aminogermylene 1 was found to be stable in toluene solution at 110 °C for 3 days without decomposition. The chalcogenation reaction of 1 aiming to synthesize heavy amides gave the head‐to‐tail type dimers of the corresponding heavy amides.

Syntheses and structures of dimesitylphosphinite complexes of alkali metals and their catalytic activity in hydrophosphorylation reactions.

Metalation of dimesitylphosphane oxide, Mes2P(O)H (1), with alkali metal reagents (nBuLi, NaH, and A(hmds); A = K, Rb, and Cs) in THF yields the corresponding dimesitylphosphinites of lithium (2-thf), sodium (3-thf), potassium (4-thf), rubidium (5-thf), and caesium (6). Their molecular structures exhibit a broad and fascinating variety. Dinuclear compounds 2-thf, 3-thf, and 5-thf have central four-membered A2O2 rings, whereas the potassium congener crystallises as a tetranuclear complex with an inner A4O4 heterocubane cage. The tetranuclear caesium congener precipitates without thf coligands and exhibits a quite unique structure in its crystalline state. Due to their catalytic activity in hydrophosphorylation reactions, we focus on the solvent-structure relationship of the potassium derivatives. In hydrocarbons, [K4(O-PMes2)4]2 (4) is formed, and bidentate Lewis bases like dme and tmeda are unable to deaggregate this tetranuclear cage compound, but bases with a higher denticity (diglyme, triglyme, and pmdeta) split this cage compound into dinuclear complexes with central K2O2 rings. In addition, very bulky P-bound aryl groups like 2,4,6-triisopropylphenyl in dinuclear 8-thf hinder the formation of tetranuclear cage compounds, whereas 2-methylnaphthyl substituents are not bulky enough and the tetranuclear cage compound 7-thf is stabilised. For the 2,4,6-triisopropylphenyl substituent, the rubidium and caesium congeners 11 and 12 crystallise with two central A2O2 rings interconnected by π-interactions. A heteroleptic potassium complex 9-hmds, containing hmds as well as phosphinite anions, represents a snapshot on the way from the starting K(hmds) to the phosphinite-based heterocubane congener. Finally, heterobimetallic [{(thf)K}2Mg(O-PMes2)4] (10-thf) with tetrahedrally coordinated Mg centres has been isolated.

Coinage metal-ethylene complexes of sterically demanding 1,10-phenanthroline ligands.

Phenanthroline-based ligands with bulky aryl groups flanking the metal binding pocket enabled the synthesis and detailed investigation of ethylene complexes of copper(I), silver(I), and gold(I), including structural data of [{2,9-bis(2,4,6-triisopropylphenyl)-1,10-phenanthroline}M(C2H4)][SbF6] (M = Cu, Ag, Au), Additionally, a related copper(I)-ethylene complex with a highly fluorinated ligand is also reported. Gold(I) affects the ethylene moiety significantly as evident from the notable upfield coordination shifts of ethylene carbon signals in the NMR and lengthening of the ethylene CC bond length. Silver(I) forms the weakest bond with ethylene in this series of isoleptic, group 11 metal-ethylene complexes. Preliminary catalytic investigations underscore the potential of copper complexes, particularly those with weakly coordinating supporting ligands, as effective catalysts for C(sp3)-H functionalization through trifluoromethyl carbene insertion.

Group 11 complexes of a bulky triazene ligand.

A new triazene ligand was prepared by the reaction of the bulky aryl azide, TerMesN3, (2,6-bis(2,4,6-trimethylphenyl)phenyl azide), with the bulky N-heterocyclic carbene (NHC), SIPr (N,N'-2,6-bis(diisopropylphenyl)-3,4-dihydroimidazol-2-ylidene). The steric bulk of these two groups leads to perpendicular bonding of the NHC-N3 plane and the aryl group which provides immense steric crowding around the triazene core. The corresponding π-conjugated triazene ligand was utilized as a neutral, monodentate ligand which results in monomeric Cu(I)Cl, Ag(I)OTf, and Au(I)Cl complexes. Instability of the π-conjugated triazene Au(I)Cl complex was observed, even under inert conditions. When dissolved and photolyzed in THF with workup in isopropanol, the compound decomposes forming [(SIPrNH)2Au(I)][Au(I)Cl2] a relatively stable compound to light, moisture, and water - alongside the formation of gold nanoparticles which were characterized using scanning electron microscopy with energy dispersive spectroscopy.

The Facile Hydrolysis of Imidazolinium Chlorides (N-Heterocyclic Carbene Precursors) Under Basic Aqueous Conditions.

The hydrolysis of imidazolinium chlorides takes place readily in a basic water/dichloromethane biphasic mixture at room temperature. Experimental parameters were optimized to afford full conversions and high yields of γ-aminoformamides starting from twelve symmetrical substrates with alkyl or aryl substituents on their nitrogen atoms, and five unsymmetrical 1-alkyl-3-arylimidazolinium chlorides. NMR and XRD analyses showed that the cleavage of unsymmetrical salts led to γ-alkylamino-N-arylformamides with a high regioselectivity and that bulky alkyl or aryl groups on the formamide moiety led to the isolation of the (E)-isomer in high stereoisomeric purity (>95 %), whereas smaller and more flexible alkyl substituents afforded mixtures of (E)- and (Z)-rotamers. Control experiments showed that the hydrolysis of 1,3-dimesitylimidazolinium chloride (SIMes ⋅ HCl) did not occur readily in pure or acidic water and that the presence of bulky aromatic substituents on the nitrogen atoms of 1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride (SIDip ⋅ HCl) efficiently slowed down its hydrolysis under basic aqueous conditions. Most strikingly, this work highlighted the critical influence of the counteranion on the reactivity of imidazolinium cations. Indeed, the chloride salts underwent a facile hydrolysis in the presence of water and Na2 CO3 , whereas various other NHC ⋅ HX derivatives reacted much slower or remained essentially inert under these conditions.

Effect of Guanine Adduct Size, Shape, and Linker Type on the Conformation of Adducted DNA: A DFT and Molecular Dynamics Study.

DNA is damaged through various exogenous sources (e.g., automobile exhaust, tobacco smoke, and processed foods), which can yield diverse C8-dG bulky aryl adducts. Adducts are known to induce structural changes to DNA that can lead to various biological outcomes, ranging from cell death to diseases such as cancer. Unfortunately, the relationship between the chemical composition of the damaged product, the adducted DNA structure, and the biological consequences is not well understood, which limits the development of disease detection and prevention strategies. The present study uses density functional theory (DFT) calculations and quintuplicate 1 μs molecular dynamics (MD) simulations to characterize the structure of DNA containing 21 model C8-dG adducts that systematically differ in size (phenyl to pyrenyl), shape (α (2,3), β (3,4) fusion, or ring substitution), and nucleobase-aryl group linkage (N, O, and C-linked). DFT calculations reveal that the inherent structural features of the G nucleobase adducts are impacted by linker type and bulky moiety shape, but not size, with the conformational flexibility reducing with α-ring fusion and linker composition as N > O > C. These structural properties are maintained in nucleoside models, which also reveal an increased propensity for anti-to-syn rotation about the glycosidic bond with N < O < C linker type. Although these diverse chemical features do not influence the global structure of adducted DNA, the adducts differentially impact the conformation local to the adducted site, including the relative populations of structures with the bulky moiety in the major groove (B conformer) and intercalated (stacked) into the helix (S conformer). Specifically, while the smallest phenyl adducts favor the B conformation and the largest pyrenyl-derived adducts stabilize the S conformation, the B/S ratio decreases with an increase in ring size and N > O > C linker composition. The shape and size (length) of the adduct can further finetune the B/S ratio, with β-fused naphthyl or α-fused phenanthryl N-linked adducts and O or C-linked adducts containing ring substitution increasing the prevalence of the S adducted DNA conformation. Overall, this work uncovers the significant effect of bulky moiety size and linker type, as well as the lesser impact of aryl group shape, on adducted DNA structure, which suggests differential replication and repair outcomes, and thereby represents an important step toward rationalizing connections between the structure and biological consequences of diverse DNA adducts.

Rhodium-Catalyzed Asymmetric Arylation-Induced Glycolate Aldol Additions of Silyl Glyoxylates.

(Diene)Rh(I) complexes catalyze the stereoselective three-component coupling of silyl glyoxylates, arylboronic acids, and aldehydes to give glycolate aldol products. The participation of Rh-alkoxides in the requisite Brook rearrangement was established through two component Rh-catalyzed couplings of silyl glyoxylates with ArB(OH)2 to give silyl-protected mandelate derivatives. The intermediacy of a chiral Rh-enolate was inferred through enantioselective protonation using a chiral Rh-catalyst. Diastereoselective three-component couplings with aldehydes as terminating electrophiles to give racemic products were best achieved with a bulky aryl ester on the silyl glyoxylate reagent. Optimal enantioselective couplings were carried out with the tert-butyl ester variant using an anisole-derived enantiopure tricyclo[3.2.2.02,4 ]nonadiene ligand.

Rhodium‐Catalyzed Asymmetric Arylation‐Induced Glycolate Aldol Additions of Silyl Glyoxylates

Abstract(Diene)Rh(I) complexes catalyze the stereoselective three‐component coupling of silyl glyoxylates, arylboronic acids, and aldehydes to give glycolate aldol products. The participation of Rh‐alkoxides in the requisite Brook rearrangement was established through two component Rh‐catalyzed couplings of silyl glyoxylates with ArB(OH)2 to give silyl‐protected mandelate derivatives. The intermediacy of a chiral Rh‐enolate was inferred through enantioselective protonation using a chiral Rh‐catalyst. Diastereoselective three‐component couplings with aldehydes as terminating electrophiles to give racemic products were best achieved with a bulky aryl ester on the silyl glyoxylate reagent. Optimal enantioselective couplings were carried out with the tert‐butyl ester variant using an anisole‐derived enantiopure tricyclo[3.2.2.02,4]nonadiene ligand.

Highly Ion-Conductive and Alkaline Stable Anion Exchange Membranes Containing Bulky Aryl Units and Symmetric bis-Piperidinium Branches

The challenge in developing high-performance anion exchange membranes (AEMs) involves achieving high ion conductivity while maintaining sufficient alkaline and mechanical stability. In this work, an aromatic monomer [bis(4′-(1,5-dibromopentan-3-yl)phenyl)-1,4-terphenyl (BBTP)] with a bulky aryl unit and symmetric dibrominated branches was first designed and synthesized. Then, BBTP was used to prepare aryl ether-free AEMs (QPTPDP-x-OH) via the superacid-catalyzed polyhydroxyalkylation and Menshutkin reactions. Due to the several structural advantages of BBTP, QPTPDP-x-OH membranes reached high hydroxide conductivity up to 161.5 mS cm–1 at 80 °C while maintaining good dimensional stability. Moreover, the membranes exhibited high alkaline stability with the conductivity retention above 80% after soaking in 5 M NaOH at 80 °C for 1200 h. In addition, QPTPDP-30-OH membranes achieved a peak power density of 407.8 mW cm–2 in H2–O2 fuel cells at 60 °C. The design strategy used in this work provided insights into the development of next-generation AEMs with high performance.