Binuclear Ruthenium Complexes with Benzo[1,2‐b;4,5‐b′]dithiophene Analogues as Bridge Ligands: Syntheses,Characterization and Notable Difference on Electronic Coupling

Diruthenium ethynyl complexes 1 – 3 ( 1 : 1,5‐dithia‐s‐indacene‐4,8‐dione; 2 : 4,8‐diethoxybenzo[1,2‐b:4,5‐ b']dithiophene; 3 : 4,8‐didodecyloxybenzo[1,2‐b:4,5‐b']dithiophene) have been synthesized by incorporating the respective conjugated heterocyclic spacer and characterized by NMR and elemental analysis. The effects of bridge ligands’ properties on electronic coupling between redox‐active ruthenium terminal groups were investigated by electrochemistry, UV /vis/near‐IR and IR spectroelectrochemistry combined with density functional theory (DFT ) and time‐dependent DFT calculations. Electrochemistry results indicated that complexes 1 – 3 exhibit two fully reversible oxidation waves, and complexes 2 and 3 with electron‐rich and π‐conjuagted bridge ligands are characterized by excellent electrochemical properties. Furthermore, the larger ν(C ≡ C) separation from the IR spectroelectrochemical results of 2 and 3 and the intense NIR absorption features of singly oxidized species 2 ⁺ and 3 ⁺ revealed that their molecular skeletons have superior abilities to delocalize the positive charge. The spin density distribution from DFT calculations proved the conclusions of this study.     

Ruthenium‐Grafted Vinylhelicenes: Chiroptical Properties and Redox Switching

The properties of mono‐ and bis‐Ru–vinyl[6]helicene complexes ( 2 a and 2 b , respectively), recently synthesized by using molecular engineering of helicenes based on the grafting of lateral organometallic substituents on the π‐helical backbone through a vinyl bridge, are presented. These helicene derivatives are thoroughly characterized, with special attention given to their chiroptical properties and redox switching activity. The UV/Vis and electronic circular dichroism (ECD) spectra of P and M enantiopure species, both in the neutral and oxidized states ([ 2 a ] ^{. +}, [ 2 b ] ^{. +}, and [ 2 b ]²⁺), are analyzed with the aid of quantum‐chemical calculations. The extended π‐conjugation facilitated by the vinyl moiety, clearly visible in the electronic structures of 2 a , b , introduces new active bands in the ECD spectra that consequently lead to a significant increase in optical rotation of Ru–vinylhelicenes compared with the organic precursors. The vibrational circular dichroism (VCD) spectra were measured and calculated for both the organic and organometallic species and constitute the first examples of VCD for metal‐based helicene derivatives. Finally, the redox‐triggered chiroptical switching activity of 2 a , b is examined in detail by using ECD spectroscopy. The modifications of the ECD spectra in the UV/Vis and NIR region are well reproduced and rationalized by calculations.     

A Quintuple [6]Helicene with a Corannulene Core as a C5‐Symmetric Propeller‐Shaped π‐System

The synthesis and structural analysis of a quintuple [6]helicene with a corannulene core is reported. The compound was synthesized from corannulene in three steps including a five‐fold intramolecular direct arylation. X‐ray crystallographic analysis revealed a C₅‐symmetric propeller‐shaped structure and one‐dimensional alignment in the solid state. The enantiomers of the quintuple [6]helicene were successfully separated by HPLC, and the chirality of the two fractions was identified by CD spectroscopy. A kinetic study yielded a racemization barrier of 34.2 kcal mol^?1, which is slightly lower than that of pristine [6]helicene. DFT calculations indicate a rapid bowl‐to‐bowl inversion of the corannulene moiety and a step‐by‐step chiral inversion pathway for the five [6]helicene moieties.     

Closed Pentaaza[9]helicene and Hexathia[9]/[5]helicene: Oxidative Fusion Reactions of ortho‐Phenylene‐Bridged Cyclic Hexapyrroles and Hexathiophenes

Oxidative fusion reactions of ortho ‐phenylene‐bridged cyclic hexapyrroles and hexathiophenes furnished novel closed helicenes in a selective manner. X‐Ray diffraction analysis unambiguously revealed the structures to be a closed pentaaza[9]helicene, the longest azahelicene reported so far, and an unexpected double‐helical structure of hexathia[9]/[5]helicene, whose formation was assumed to result from multiple oxidative fusion along with a 1,2‐aryl shift. The pentaaza[9]helicene exhibited well‐defined emission with high fluorescence quantum yield (Φ _F=0.31) among the known [9]helicenes. Chiral resolution of the racemic pentaaza[9]helicene and hexathia[9]/[5]helicene were achieved by chiral‐phase HPLC and the enantiomers were characterized by circular dichroism spectra and DFT calculations.     

Twisted Polycyclic Arenes from Tetranaphthyldiphenylbenzenes by Controlling the Scholl Reaction with Substituents

Herein, we report two new types of twisted polycyclic arenes ( 2 a , b and 3 a , b ) with constitutionally isomeric π‐backbones, which are synthesized by controlling the Scholl reaction of 1,2,4,5‐tetra(naphth‐2‐yl)‐3,6‐diphenylbenzene ( 1 ) with properly positioned electron‐donating substituents. With a polycyclic backbone containing two [5]helicene and four [4]helicene moieties, 2 a and b are new members of multiple helicenes with interesting stereochemistries. The as‐synthesized 2 a and b are the twisted isomers, and thermal isomerization of twisted‐ 2 b results in anti‐ 2 b , a more stable stereoisomer. Both twisted‐ and anti‐ 2 b have been fully characterized, and the thermal isomerization of twisted‐ 2 b has been studied with ¹H NMR spectroscopy and DFT calculations. Compounds 3 a and b are new members of twistacenes, the benzannulated pentacene backbone of which exhibits an end‐to‐end twist as found from the crystal structure. Twisted‐ and anti‐ 2 b are also found to function as p‐type semiconductors in solution‐processed thin film transistors, whereas the thin films of 3 b appear insulating presumably due to the lack of π–π interactions.     

Synthesis of Optically Pure Helicene Metallocenes

Two types of ruthenocenes and a ferrocene coordinated by rac ‐9H ‐cyclopenta[1,2‐c :4,3‐c ′]diphenanthrenyl anion(s), a [7]helicene with a cyclopentadienyl moiety at the center of its skeleton, were successfully synthesized: mono‐helicene ruthenocene 1 and its iron analogue 1_Fe with one [7]helicene ligand bound to the central metal, and bis‐helicene ruthenocene 2 with two [7]helicenes. Starting from a racemic mixture of the ligand precursor, rac ‐ 2 and meso ‐ 2 were obtained in a 7:3 ratio. Since the [7]helicene has a high racemization barrier, enantiomers of the complexes were isolated in their pure forms; they showed large optical rotations and intense circular dichroism (CD) responses.     

Diastereo‐ and Enantioselective Synthesis of Organometallic Bis(helicene)s by a Combination of C?H Activation and Dynamic Isomerization

Homochiral and heterochiral cis‐bis‐cycloplatinated‐[6]helicene derivatives 1 b^{1, 2} , as representative examples of platina[6]helicenes that share a common platinum center, have been prepared. A diastereo‐ and enantioselective synthesis, which combines CH activation and dynamic isomerization from heterochiral structure 1 b² into homochiral structure 1 b¹ , is also described. Overall, this isomerization process results in the transfer of chiral information from one helicene moiety to the other one. The chiroptical properties of homochiral (P)‐ and (M)‐ 1 b¹ were greatly modified upon oxidation into their corresponding (P)‐ and (M)‐diiodo‐Pt^IV complexes ( 5 ). The changes were also analyzed by performing theoretical calculations. C? H activation in the synthesis of organometallic helicenes is further demonstrated by the preparation of cis‐bis‐cycloplatinated‐[8]helicene 1 c .     

Reaction of 2,3‐Dichloro‐1,4‐Naphthoquinone with 1‐Phenylbiguanide and 2‐Guanidinebenzimidazole

When 2,3‐dichloro‐1,4‐naphthoquinone (DCHNQ) ( 1 ) is allowed to react with 1‐phenylbiguanide (PBG) ( 2 ), 4‐chloro‐2,5‐dihydro‐2,5‐dioxonaphtho[1,2‐d]imidazole‐3‐carboxylic acid phenyl amide ( 4 ), 6‐chloro‐8‐phenylamino‐9H‐7,9,11‐triaza‐cyclohepta[a]naphthalene‐5,10‐dione ( 5 ) and 4‐dimethyl‐amino‐5,10‐dioxo‐2‐phenylimino‐5,10‐dihydro‐2H‐benzo[g]quinazoline‐1‐carboxylic acid amide ( 6 ) were obtained. While on reacting 1 with 2‐guanidinebenzimidazole (GBI) ( 3 ) the products are 3‐(1H‐benzoimidazol‐2‐yl)‐4‐chloro‐3H‐naphtho[1,2‐d]imidazole‐2,5‐dione ( 7 ) and 3‐[3‐(1H‐benzoimidazol‐2‐yl)‐ureido]‐1,4‐dioxo‐1,4‐dihydronaphthalene‐2‐carboxylic acid dimethylamide ( 8 ).     

Synthesis,Crystal Structure and Photophysical Properties of Pyrene–Helicene Hybrids

Synthesis of helically chiral aromatics resulting from fusion of pyrene and [4]‐ or [5]helicene has been accomplished using photoredox catalysis employing a Cu‐based sensitizer as the key step. Photocyclisation experiments for the synthesis of the target compounds were carried out in batch and using continuous flow strategies. The solid‐state structures, UV/Vis absorption spectra and fluorescence spectra of the pyrene–helicene hybrids were investigated and compared to that of the parent [5]helicene to discern the effects of merging a pyrene moiety within a helicene skeleton. The studies demonstrated that pyrene–helicene hybrids adopt co‐planar or stacked arrangements in the solid state, in contrast to the solid‐state structure of the parent [5]helicene. The UV/Vis and fluorescence spectra of the pyrene–helicene hybrids exhibited strong red‐shifts when compared to the parent [5]helicene. DFT calculations suggest that the strategy of extending the π surface in the y axis of the helicenes increased their HOMO levels while also decreasing their LUMO levels, resulting in significantly reduced band gaps.     

S-shaped para-Quinodimethane-Embedded Double [6]Helicene and Its Charged Species Showing Open-Shell Diradical Character

Helicenes and extended helical π-conjugated compounds have been widely studied, but most of the systems contain only aromatic benzene or heterocyclic rings, showing local aromatic character. Herein, new S-shaped double [6]helicene 1 , which has two embedded para-quinodimethane (p-QDM) units, is reported. Due to the existence of a proaromatic quinoidal substructure, it has open-shell diradical character. Its model compound, C-shaped single [6]helicene 2 containing one p-QDM unit, was also synthesized and compared. Their ground-state structures and electronic properties were systematically studied by a combination of various experimental methods assisted by theoretical calculations. Compound 1 has a double-helical structure in the crystal, with the two terminal [6]helicene units bent in opposite directions (i.e., anti form). However, an anti/syn isomerization process with a moderate interconversion energy barrier was observed on the NMR timescale. Compound 1 shows amphoteric redox behavior. It also exhibits open-shell diradical character (y₀=12.1 %) and a small singlet–triplet gap. On the other hand, compound 2 has a typical closed-shell nature. The dication and dianion of 1 also show open-shell diradical character. The dianion of 2 and the tetraanion of 1 exhibit similar electronic structures to their respective isoelectronic structures, that is, [6]helicene and a double [6]helicene. This work provides some insights into the design and synthesis of stable helical π systems with open-shell diradical character and magnetic activity.     

On the π‐Electron Distribution in Biphenylene Analogues

The bonding situation in a series of biphenylene analogues – benzo[b]biphenylene and its dication, 4,10‐dibromobenzo[b]biphenylene, naphtho[2,3‐b]biphenylene and its dianion, benzo[a]biphenylene, (biphenylene)tricarbonylchromium, benzo[3,4]cyclobuta[1,2‐c]thiophene, benzo[3,4]cyclobuta[1,2‐c]thiophene 2‐oxide, benzo[3,4]cyclobuta[1,2‐c]thiophene 2,2‐dioxide, 4,10‐diazabenzo[b]biphenylene, biphenylene‐2,3‐dione, benzo[3,4]cyclobuta[1,2‐b]anthracene‐6,11‐dione, and 3,4‐dihydro‐2H‐benzo[3,4]cyclobuta[1,2]cycloheptene – where one of the two benzo rings of biphenylene is replaced by a different π‐system (B) was investigated on the basis of the NMR parameters of these systems. From the vicinal ¹H,¹H spin‐spin coupling constants, the electronic structure of the remaining benzo ring (A) is derived via the Q‐value method. It is found that increasing tendency of B to tolerate exocyclic double bonds at the central four‐membered ring of these systems favors increased π‐electron delocalization in the A ring. The analysis of the chemical shifts supports this conclusion. NICS (nucleus‐independent chemical shift) values as well as C,C bond lengths derived from ab initio calculations are in excellent agreement with the experimental data. The charged systems benzo[b]biphenylene dication and naphtho[2,3‐b]biphenylene dianion ( 7 ²⁻) are also studied by ¹³C NMR measurements. The charge distribution found closely resembles the predictions of the simple HMO model and reveals that 7 ²⁻ can be regarded as a benzo[3,4]cyclobuta[1,2‐b]‐substituted anthracene dianion. It is shown that the orientation of the tricarbonylchromium group in complexes of benzenoid aromatics can be derived from the vicinal ¹H,¹H coupling constants.     

Synthesis,DNA‐Binding and Photocleavage Studies of the Ruthenium(II) Complexes [Ru(phen)2(ppd)]2+ and [Ru(phen)(ppd)2]2+ (ppd=Pteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione,phen=1,10‐Phenanthroline)

Two new complexes, [Ru(phen)₂(ppd)]²⁺ ( 1 ) and [Ru(phen)(ppd)₂]²⁺ ( 2 ) (ppd=pteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione, phen=1,10‐phenanthroline) were synthesized and characterized by ES‐MS, ¹H‐NMR spectroscopy, and elemental analysis. The intercalative DNA‐binding properties of 1 and 2 were investigated by absorption‐spectroscopy titration, luminescence‐spectroscopy studies, thermal denaturation, and viscosity measurements. The theoretical aspects were further discussed by comparative studies of 1 and 2 by means of DFT calculations and molecular‐orbital theory. Photoactivated cleavage of pBR322 DNA by the two complexes were also studied, and 2 was found to be a much better photocleavage reagent than 1 . The mechanism studies revealed that singlet oxygen and the excited‐states redox potentials of the complex may play an important role in the DNA photocleavage.     

Synthesis,Characterization, and Electrochemistry of the Manganese(I) Complexes of meso‐Substituted [14]Tribenzotriphyrins(2.1.1)

Metalation of 6,13,20,21‐tetraaryl‐22H‐[14]tribenzotriphyrins(2.1.1) (TriP, 1 a – d ) with [Mn(CO)₅Br] provided Mn^I tricarbonyl complexes of [14]tribenzotriphyrins(2.1.1) 2 a – d in 85–93 % yield. The complexes were characterized by mass spectrometry and UV/Vis absorption, IR, and NMR spectroscopy. Single‐crystal X‐ray analyses revealed that 2 b and 2 c adopt bowl‐shaped conformations. The redox properties of [(TriP)Mn^I(CO)₃] ( 2 a – d ) were studied by cyclic voltammetry. Each compound undergoes two reversible one‐electron reductions to form a porphyrin π anion radical and a dianion in CH₂Cl₂. Two oxidation waves were observed, the first of which corresponds to a metal‐centered electron‐transfer process. The redox potentials of 2 a – d are consistent with the optical spectroscopic data and the relatively narrow HOMO–LUMO gaps that were predicted in DFT calculations. The optical spectra can be assigned by using Michl’s perimeter model. TDDFT calculations predict the presence of several metal‐to‐ligand charge‐transfer bands in the L‐band region between 500 and 700 nm.     

Palladium‐Catalyzed Annulation of 9‐Halophenanthrenes with Alkynes: Synthesis,Structural Analysis,and Properties of Acephenanthrylene‐Based Derivatives

The palladium‐catalyzed annulation of 9‐bromo‐ and 9‐chlorophenanthrenes with alkynes gave 4,5‐disubstituted acephenanthrylenes in yields of 58–95 % (9 examples). Asymmetric alkynes, such as 1‐phenyl‐1‐propyne, 1‐phenyl‐1‐hexyne, and 1‐cyclopropyl‐2‐phenylethyne, regioselectively form (cyclo)alkyl‐substituted products, following the regular rule that governs the carbopalladation of alkynes. This synthetic protocol can also be utilized in annulations with several π‐extended bromoarenes, such as 7‐bromo[5]helicene, 5‐bromo[4]helicene, 9‐bromoanthracene, 3‐bromoperylene, and 3‐bromofluoranthene, to give the corresponding annulated products in moderate to good yields (51–86 %; 6 examples). Similarly, bromocorannulene produced highly curved 1,2‐disubstituted cyclopentacorannulenes. Reactions of 6,12‐dibromochrysene and 4,7‐dibromo[4]helicene with di(4‐tolyl)ethyne provided the twofold annulated products in moderate yields. 4,5‐Diphenylacephenanthrylene and 6,7‐diphenylbenzo[a]acephenanthrylene thus generated were converted into phenanthro[9,10‐e]acephenanthrylene and benzo[a]phenanthro[9,10‐e]acephenanthrylene, respectively, by oxidative cyclodehydrogenation. The structures of 4,5‐diphenylacephenanthrylene, 4,5‐diphenyldibenzo[a,l]acephenanthrylene, 1,2‐diarylcyclopentacorannulenes, and benzo[a]phenanthro[9,10‐e]acephenanthrylene were verified by X‐ray crystallography. The photophysical and electrochemical properties of the selected annulated products were investigated.     

The synthesis of new azoniathiahelicenes

Synthesis of new azonia derivatives of thia[6]helicene ( 1 ) and thia[7]helicene ( 2 ) is described. The Knoevenagel condensation of 2‐methylbenzothieno[3,2‐a]quinolizinium salt ( 8 ) with appropriate arylaldehydes yielded 2‐(arylvinyl)benzothieno[3,2‐a]quinolizinium salts ( 9 and 10 ), respectively. Photocyclization of 2‐styrylbenzothieno[3,2‐a]quinolizinium salt ( 8 ) gave 7a‐azonia‐5‐thia[6]helicene ( 1 ) in 63% yield. Similarly, 2‐[2‐(2‐naphthyl)vinyl]benzothieno[3,2‐a]quinolizinium salt ( 10 ) afforded 7a‐azonia‐5‐thia[7]helicene ( 2 ) in 56% yield. The complete and unambiguous assignment of their ¹H‐ and ¹³C‐nmr spectra was performed by utilizing two‐dimensional nmr spectroscopic methods.     

Synthesis and Properties of Brominated 6,6'-Dimethyl-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1 '-diones

Photochromic 6‐bromomethyl‐6′‐methyl‐[2,2′‐bi‐1H‐indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 2 ), 6,6′‐ bis(bromomethyl)‐[2,2′‐bi‐1H‐indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 3 ) and 6,6′‐bis(dibromomethyl)‐[2,2′‐ bi‐1H‐indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 4 ) have been synthesized from 6,6′‐dimethyl‐[2,2′‐bi‐1H‐ indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 1 ). The single crystal of 4 was obtained and its crystal structure was analyzed. The results indicate that in crystal 4 , molecular arrangement is defective tightness compared with its precursor 1 . Besides, UV‐Vis absorption spectra in CH₂Cl₂ solution, photochromic and photomagnetic properties in solid state of 2 , 3 and 4 were also investigated. The results demonstrate that when the hydrogen atoms in the methyl group on the benzene rings of biindenylidenedione were substituted by bromines, its properties could be affected considerably.     

Enantioselective Synthesis of [9]‐ and [11]Helicene‐like Molecules: Double Intramolecular [2+2+2] Cycloaddition

The enantioselective synthesis of completely ortho‐fused [9]‐ and [11]helicene‐like molecules has been achieved through a rhodium‐mediated, intramolecular, double [2+2+2] cycloaddition of phenol‐ or 2‐naphthol‐linked hexaynes. Crystal structures and photophysical properties of these [9]‐ and [11]helicene‐like molecules have also been disclosed.     

f‐Block Ansa Complexes in the Solid State: [3]Thoro‐ and [3]Uranocenophanes

The preparation of [3]thoro‐ and [3]uranocenophanes, the first structurally authenticated ansa‐bridged complexes of actinocenes, is reported. Following a flytrap route, 1,2‐bis(cyclooctatetraenyldimethylsilyl)methane was synthesized, reduced to its tetraanion, and subsequently converted into bridged uranocene and thorocene complexes by salt metathesis with the corresponding actinide tetrachlorides. In addition, their electronic structures have been investigated by experimental (UV/Vis spectroscopy, cyclic voltammetry) and theoretical (DFT) methods.     

The synthesis of azoniadithia[6]helicenes

A new short‐step synthesis of 8a‐azonia[6]helicene (1) and the novel dithieno derivatives ( 2 and 3 ) is described. Double photocyclization of 2,8‐distyrylquinolizinium salt (8) gave 1 in 35% yield. Similarly, 2,8‐bis[2‐(2‐thienyl)vinyl]‐ and 2,8‐bis[2‐(3‐thienyl)vinyl]‐quinolizinium salts ( 9 and 10 ) afforded new azonia[6]helicenes containing two thiophene rings at the ends of helix, that is 7a‐azonia‐3,12‐dithia[6]helicene (2) and 7a‐azonia‐1,14‐dithia[6]helicene (3) , in 43 and 35% yields, respectively. The total assignment of their ¹H‐ and ¹³C‐nmr spectra was performed by utilizing two‐dimensional and NOE nmr spectroscopic methods.     

Synthesis and reactions of 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]‐quinazolin‐9‐one and 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one

The reaction of 3‐N‐(2‐mercapto‐4‐oxo‐4H‐quinazolin‐3‐yl)acetamide ( 1 ) with hydrazine hydrate yielded 3‐amino‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 2 ). The reaction of 2 with o‐chlorobenzaldehyde and 2‐hydroxy‐naphthaldehyde gave the corresponding 3‐arylidene amino derivatives 3 and 4 , respectively. Condensation of 2 with 1‐nitroso‐2‐naphthol afforded the corresponding 3‐(2‐hydroxy‐naphthalen‐1‐yl‐diazenyl)‐2‐methyl‐3H‐[1,2,4]triazolo[5,1‐b]quinazolin‐9‐one ( 5 ), which on subsequent reduction by SnCl₂ and HCl gave the hydrazino derivative 6. Reaction of 2 with phenyl isothiocyanate in refluxing ethanol yielded thiourea derivative 7. Ring closure of 7 subsequently cyclized on refluxing with phencyl bromide, oxalyl dichloride and chloroacetic acid afforded the corresponding thiazolidine derivatives 8, 9 and 10 , respectively. Reaction of 2‐mercapto‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 11 ) with hydrazine hydrate afforded 2‐hydrazino‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 12 ). The reactivity 12 towards carbon disulphide, acetyl acetone and ethyl acetoacetate gave 13, 14 and 15 , respectively. Condensation of 12 with isatin afforded 2‐[N‐(2‐oxo‐1,2‐dihydroindol‐3‐ylidene)hydrazino]‐3‐phenylamino‐3H‐quinazolin‐4‐one ( 16 ). 2‐(4‐Oxo‐3‐phenylamino‐3,4‐dihydroquinazolin‐2‐ylamino)isoindole‐1,3‐dione ( 17 ) was synthesized by the reaction of 12 with phthalic anhydride. All isolated products were confirmed by their ir, ¹H nmr, ¹³C nmr and mass spectra.