Shaping a Porphyrinoid Frame by Heteroatoms Extrusion: Formation of an Expanded [22]Triphyrin(6.6.0)

An aromatic expanded triphyrin, [22]triphyrin(6.6.0) 2 , containing a pyrrole unit, a bipyrrole moiety, and annulene links, was obtained from a tellurium-containing precursor meso-tetraaryl-26,28-ditellurasapphyrin 1 . The reaction path proceeds through an acid-promoted tellurium extrusion from 1 yielding directly 2 , characterized in a dicationic form by X-ray crystallography. In solution the neutral macrocycle 2 reveals flexibility typical for annulenes and it exists as a mixture of conformers that differ by the configuration of the annulene fragments, as proven by ¹H NMR studies and analyzed by DFT methods. The conformation is controlled by protonation state, the nature of an interacting anion, solvent identity, and by interaction with water.     

8,19-Dimethyl-tetraepoxy[22]annulen(2.1.2.1): ein erstes Tetraepoxy-Verbrücktes aromatisches [22]Annulen

8,19-Dimethyl-tetraepoxy[22]annulen(2.1.2.1): The First Tetraepoxy-Bridged Aromatic[22]Annulene By McMurry reaction of 5,5′-ethylidenebis[furan-2-carbaldehyde] ( 15 ), a syn/anti mixture 16 of (E,E)- and (Z,Z)-8,19-dihydro-8,19-dimethyl-tetraepoxy[22]annulene is obtained. The (E/E)-isomers 16 are the first rotation- ally active noncyclic conjugated macrocycles, where the (E)-ethenediyl moieties rotate around the connecting single bonds. The dihydro-tetraepoxy[22]annulenes 16 are dehydrogenated by (Ph₃C)BF₄ as well as by O₂ to give the tetraepoxy[22]annulene 11 . The spectroscopic data support the character of 11 as an aromatic, diatropic ring system, which is rather sensitive towards O₂. In the oxidation mixture obtained from 11 , beside polymeric products, two compounds 19 and 20 can be isolated, carrying one and two CHO groups, respectively, resulting by oxidation of one or both Me-groups but having retained the aromatic 22π system of 11 .     

Aromatic and Antiaromatic Pathways in Triphyrin(2.1.1) Annelated with Benzo[b]heterocycles

Understanding of the aromatic properties and magnetically induced current densities of highly conjugated chromophores is important when designing molecules with strongly delocalized electronic structure. Linear extension of the triphyrin(2.1.1) skeleton with an annelated benzo[b]heterocycle fragment modifies the aromatic character by extending the electron delocalization pathway. Two-electron reduction leads to an antiaromatic triphyrin(2.1.1) ring and an aromatic benzo[b]heterocycle subunit. Current-density calculations provide detailed information about the observed pathways and their strengths.     

Synthesis and properties of trefoil-shaped tris(hexadehydrotribenzo[12]annulene) and tris(tetradehydrotribenzo[12]annulene)

[reaction: see text] Trefoil-shaped tris(hexadehydrotribenzo[12]annulene) possessing a substructure of the ultimate two-dimensional C(sp)-C(sp(2)) network, graphyne, and the related tris(tetradehydrotribenzo[12]annulene) were synthesized, and their ground- and excited-state properties were investigated.     

The synthesis and properties of free-base [14]triphyrin(2.1.1) compounds and the formation of subporphyrinoid metal complexes

The synthesis of [14]triphyrin(2.1.1) compounds is described. In contrast with conventional subporphyrins, which consistently contain a central boron atom, free-base heteroaromatic compounds can be formed. A modified Lindsey method was used to prepare a range of different [14]triphyrins(2.1.1) in yields of up to 35% based on the reaction of diethylpyrrole (1a) and fused pyrroles of bicyclo[2.2.2]octadiene (BCOD) (2a-e) and dihydroethanonaphthalene (4a) with various aryl aldehydes. The concentration of BF(3)·OEt(2) catalyst plays the key role in determining the yield of the [14]triphyrin(2.1.1) macrocycle relative to the conventional tetrapyrrole porphyrin product. Retro-Diels-Alder reactions of 2a-e and 4a result in the formation of [14]tribenzotriphyrin (2.1.1) (3a-e) and [14]trinaphthotriphyrin(2.1.1) (5a). The effects of exocyclic ring annulation on the electronic structure are examined in detail based on optical spectroscopy, theoretical calculations, and electrochemical measurements. The availability of free-base compounds enables the formation of [Re(I)(CO)(3)(triphyrin)] (6a) and [Ru(II)(CO)(2)Cl(triphyrin)] (7a) complexes based on a modified retro-Diels-Alder reaction. X-ray structures are reported for 4a and 6a.     

Tetrakisdehydro[14]annuleno[20]annulene

Tetrakisdehydro[14]annuleno[20]annulene consisting of an aromatic bisdehydro[14]annulene and an antiaromatic trisdehydro[20]annulene has been synthesized. The ¹H NHR spectra clearly indicate the induction of para- and diamagnetic ring currents in each of the [4n]- and [4n+2]-rings, respectively.     

Trisdehydro[14]annuleno[16]annulene

Trisdehydro[14]annuleno[16]annulene consisting of an aromatic bisdehydro[14]annulene and an antiaromatic bisdehydro[16]annulene has been synthesized. The strong paratropicity was observed in the [16]annulene moiety being comparable with that of extremely unstable parent bisdehydro[16]annulene.     

Preparation,Spectroscopic Properties and Characterization of Oxovanadium(IV), Isothiocyanatomanganese(III), Cyanocobalt(III) and Cobalt(II) Complexes with a Bis-Crown Ether Tetraaza[14]Annulene

Oxovanadium(IV), isothiocyanatomanganese(III), cyanocobalt(III) and cobalt(II) complexes of tetraaza[14]annulene appended with two crown ethers at 2,3- and 11,12-positions have been prepared. Cation complexation behavior of these cavity-bearing tetraaza[14]annulene complexes has been investigated by optical absorption methods. The cation K + , which necessitates two crown ether cavities for complexation, induces dimerization of the tetraaza[14]annulene complexes, whereas the Na + does not. Formation of the sandwich complexes due to dimerization is hindered by the steric interactions involving the axial ligand as judged by the blue shift of the intense band around 385-425 nm. Judging from its ESR spectrum, the cobalt(II) complex becomes a monomeric dioxygen complex of a 1 : 1 molar ratio in the presence of O 2 and pyridine at 77 K.     

Annulenoide Tetrathiafulvalene:, 5,16‐Bis(1,3‐benzodithiol‐2‐yliden)‐5,16‐dihydrotetraepoxy‐ und 5,16‐Bis(1,3‐benzodithiol‐2‐yliden)‐5,16‐dihydrotetraepithio[22]annulene(2.1.2.1)

Annulenoid Tetrathiafulvalenes: 5,16‐Bis(1,3‐benzodithiol‐2‐ylidene)‐5,16‐dihydrotetraepoxy‐ and 5,16‐Bis(1,3‐benzodithiol‐2‐ylidene)‐5,16‐dihydrotetraepithio[22]annulenes(2.1.2.1) The title compounds are among the first tetrathiafulvalenes with annulene spacers, here with tetraepoxy‐[22]annulene(2.1.2.1) (see 3a ), tetraepithio[22]annulene(2.1.2.1) (see 3b ), and diepithiodiepoxy[22]annulene(2.1.2.1) (see 23 ) units. The annulenoid tetrathiafulvalenes 3a and 3b are prepared by cyclizing McMurry coupling of the 5,5′‐(1,3‐benzodithiol‐2‐ylidenemethylene)bis[furan‐ or thiophene‐2‐carbaldehydes] ( 8a or 8b , resp.) or by Wittig reaction of (1,3‐benzodithiol‐2‐yl)tributylphosphonium tetrafluoroborate ( 13b ) with tetraepoxy[22]annulene(2.1.2.1)‐1,12‐dione 20 (formation of 3a ) or diepithiodiepoxy[22]annulene(2.1.2.1)‐1,12‐dione 22 (formation of 23 ). The annulenoide tetrathiafulvalene 3a is obtained as a mixture of the isomers (E,E)‐ and (Z,Z)‐ 3a . At 130°, (Z,Z)‐ 3a rearranges quantitatively into the (E,E)‐isomer. Isomer (E,E)‐ 3a is a dynamic molecule, where the (E)‐ethene‐1,2‐diyl bridges rotate around the adjacent σ‐bonds. The tetraepithioannulene derivative 3b as well as 23 only exist in the (Z,Z)‐configuration. The oxidation of (E,E/Z,Z)‐ 3a with Br₂ yields the annulene‐bridged tetrathiafulvalene dication (E,E)‐ 3a _Ox, while with 4,5‐dichloro‐3,6‐dioxocyclohexa‐1,4‐diene‐1,2‐dicarbonitrile (DDQ) obviously only the radical cation 3a _Sem is formed, which belongs to the class of cyanine‐like violenes. The annulenoide tetrathiafulvalenes 3b and 23 , which exist only in the (Z,Z)‐configuration, obviously for steric reasons, cannot be oxidized by DDQ. Electrochemical studies are in agreement with these results.     

Tetrakisdehydro[16]annuleno[18]annulene

Tetrakisdehydro[16]annuleno consisting of trisdehydro[16]annulene and bisdehydro[18] annulene has been synthesized. Induction of para- and diamagnetic ring currents in 16- and 18-membered rings, respectively, was clearly recognized by the ¹H NMR spectroscopy. A marked suppresion of the diatropicity in the 18π moiety was observed in the same trend as observed in tetrakisdehydro[14]annuleno[16]annulene.     

Aromaticity and Homoaromaticity in Methano[10]annulenes

Aromaticity and neutral homoaromaticity have been evaluated in methano[10]annulenes systems, 1,4-methano[10]annulene (1), 1,5-methano[10]annulene (2), and 1,6-methano[10]annulene (3). C-C bond lengths indicate that 1 presents higher bond alternation than 2 and 3. The relative energies were determined at the B3LYP/6-311+G(d,p) level, and they pointed out that 3 is the most stable isomer. Strain energies, evaluated employing homodesmotic reactions, show the same order as the relative energies. Through a decomposition of strain energies, it could be concluded that the rings absorb more tension than the bridges. The changes in aromaticity were evaluated by magnetic susceptibilities, chiM, HOMA, NICS, and resonance energies, RE. HOMA, RE, and chiM indicate that 2 and 3 are strongly, and 1 is fairly, aromatic. NICS does not provide reliable results, due to interference of ring and bridge atoms. NBO analysis presents some interactions that suggest the existence of neutral homoaromaticity. GPA indices (evaluated at the B3LYP/6-31G* level) point out that homoaromaticity plays a relevant role only in 3. Moreover, this work is the first in the current literature that studies 1,4-methano[10]annulene (1).     

An ortho-fused tetrakisdehydro[14]annuleno[14]annulene consisting of two different types of bisdehydro[14]annulenes

Tetrakisdehydro[14]annuleno[14]annulene consisting of ‘acetylene-cumulene’ bisdehydro[14]annulene and Sondheimer's bishydro[14]annulene has been synthesized. It was found that a strong diatropicity was observed in the ‘acetylene-cumulene’ bisdehydro[14]annulene moiety, whereas diatropicity of another bisdehydro[14]annulene moiety shows marked decrease comparable with that of napthobisdehydro[14]annulene synthesized by Sondheimer.     

Tetrakisdehydro[14]annuleno[16]annulene

Tetrakisdehydro[14]annuleno[16]annulene consisting of an aromatic bisdehydro[14]-annulene and an antiaromatic trisdehydro[16]annulene has been synthesized. The ¹H NMR parameters clearly indicate the strong paratropicity and diatropicity of the 16-membered and 14-membered rings, respectively.     

Diepoxy[18]annulene(10.0) : (Z,E,Z,E,Z)‐Diepoxy[18]annulen(10.0) – ein hochdynamisches Annulen

Diepoxy[18]annulenes(10.0): ( Z , E , Z , E , Z )‐Diepoxy[18]annulene(10.0) – a Highly Dynamic Annulene The McMurry reaction of (all‐E)‐5,5′‐([2,2′‐bifuran]‐5,5′‐diyl)bis[penta‐2,4‐dienal] ( 13 ) only occurs intramolecularly to give a mixture of the diepoxy[18]annulenes(10.0) 6 and 7 . Tetraepoxy[36]annulene(10.0.10.0) resulting from an intermolecular McMurry reaction is not formed. According to spectroscopic data, 6 is (Z,E,Z,E,Z)‐ and 7 (Z,E,E,Z,E)‐configured. The ¹H‐NMR data confirm that in 6 the (E)‐ethene‐1,2‐diyl bonds (C(11)=C(12) and C(15)=C(16)) rotate around the adjacent σ‐bonds. Beginning at −70°, this rotation freezes, and 6 is becoming a diatropic aromatic ring system. Beside [18]annulene itself, (Z,E,Z,E,Z)‐diepoxy[18]annulene(10.0) 6 is the only hitherto known [18]annulene derivative with dynamic properties.     

Tetraepoxy[32]annulene(4.4.4.4) und `Tetraoxa[30]porphyrin(4.4.4.4)'‐Dikationen

Tetraepoxy[32]annulenes(4.4.4.4) and `Tetraoxa[30]porphyrin(4.4.4.4)' Dications Of the tetraepoxy[32]annulenes as well as the `tetraoxa[30]porphyrin' dications, hithertoo only the (8.0.8.0) and the (6.2.6.2) systems are known to exist in several geometric isomers and to possess antiaromatic and aromatic character, respectively. Here we describe the still missing symmetric member of the [32]annulenes, the tetraepoxy[32]annulene(4.4.4.4) 1 and the corresponding `tetraoxa[30]porphyrin(4.4.4.4)' dication 2 . The cyclizing Wittig reaction of the dialdehyde 3 with the bis‐phosphonium salt 7 at 70° yields the configurational isomers 1a (ZE,EE,EZ,EE), 1b (ZE,EE,EE,EE), and 1c (EZ,EE,EZ,EE). All isomers are antiaromatic; in 1a and 1c , the two (E,E)‐buta‐1,3‐diene‐1,4‐diyl bridges rotate around the adjacent σ‐bonds; the rigidity of 1b with 3 (E,E) bridges prevents any dynamic character. The Wittig reaction of 3 with 7 at 20° only yields the kinetically controlled annulene 1c , and at 120°, an excess of the thermodynamically most stable isomer 1a is formed. The structure of 1 is elucidated mainly by COSY and NOESY experiments, and the dynamic character of 1a and 1c is established by temperature‐dependent <sup>1</sup>H‐NMR spectroscopy. The oxidation of the isomer mixture 1a – c with 4,5‐dichloro‐3,6‐dioxocyclohexa‐1,4‐diene‐1,2‐dicarbonitrile (DDQ) gives two isomeric `tetraoxa[30]porphyrin(4.4.4.4)' dications 2′ and 2″ , which are frozen conformers with the same (EZ,EE,EZ,EE)‐configuration and geometrically related to 1c . Semiempirical calculations of 1 and 2 are in full agreement with the experimental results.     

Theoretical determination of molecular structure. Conformation of some benzo[10]-annulenes and [10]-annulene

Summary The AM1 method was used to carry out a theoretical study of optimized geometries and energies of some benzoannulenes. The transition state of the transformation of the benzo[10]annulene was also determined. The transition state has been located.     

Preparation and characterization of tetraaza[14]annulene and its nickel(ii) and copper(II) complexes with crown ether functionalities

Three new organic hosts are described that contain a tetraaza[14]annulene core to which two crown ether voids are attached. These hosts include a free base tetraaza[14]annulene and/or its complexes with benzo-15-crown-5 rings. The crown tetraaza[14]annulene is synthesized from tetraaza[14]annulene and 4′-chloroformylbenzo-15-crown-5. Its nickel(II) and copper(II) complexes are prepared in a similar manner as above. In solution the compounds do not tend to form aggregates. However, aggregation is affected by the presence of alkali-metal salts, which coordinate to the crowns. Li⁺ and Na⁺ cations with diameters that match the diameters of the crown ether rings form 1:2 host-guest complexes. Complexes with 2:2 host-guest stoichiometry are formed when the diameters of K⁺ and Cs⁺ cations exceed that of the crown ether rings. Nevertheless, it is weak for the present macrocycle and its complexes to be inclined to form dimers owing to the steric hindrance of the substituent groups and owing to restraining the rotation of the carbonyl bond connecting the crown ether group.     

Crystal and Molecular Structure of the Macrocyclic Nickel (II) Complex Ni(C22H22H4): Dibenzo[b,i][5, 7, 12, 14] Tetramethyl [1, 4, 8, 11] Tetraazacyclotetradeca-2, 4, 7, 9, 12, 14-Hexaeneatonickel (II)

The crystal and molecular structure of the four-coordinate complex Ni(C₂₂H₂₂N₄) containing the tetramethyldibenzotetraaza[14] annulene ligand has been determined from three-dimensional X-ray diffraction data. The complex crystallized in the monoclinic space group C_2h⁵-P2₁/n with cell dimensions a=14.7967(10), b=11.2169(6), c=11.4510(6) Å, and β=98.467(5)° with Z=4. The final agreement indices from the least-square refinement of 245 variables with 3111 observations F>3σ(F), are R=0.050, R_w=0.037. The structure has a pronounced saddle-shaped conformation with Ni atom at the saddle point coordinated to four nitrogen atoms. The average Ni-N distance is 1.866(3) Å. The delocalized propane-1,3-diiminato chelate rings and the benzene rings are linked by nominally single C-N bonds.     

Perimeter-Type Structures in Charged [4n + 2] Annuleno [4n + 2] annulenes. The Importance of the Frontier-Orbitals

The tetra(tert-butyl)[14]annuleno[14]annulene 1 is transformed, via alkali metal reduction, into its radical monoanion, dianion, radical trianion, and tetraanion. The paramagnetic species are characterized by ESR and ENDOR spectroscopy and the diamagnetic species by ¹H- and ¹³C-NMR spectroscopy. Well-resolved ESR and NMR spectra can only be obtained, if the reduction is carefully monitored. For the interpretation of the data, the ions derived from the structurally related [14]- and [22]annulenes 3 and 5 as well from the tetra(tert-butyl)[14]annuleno[18]annulene 2 serve as suitable model compounds. While the behavior of the neutral annulenoannulene 1 is governed by that of the [14]annulene-subunit, the corresponding ionic systems can best be described as macrocyclic perimeters. This outcome can be rationalized by the nodal properties of the frontier MO's.     

The second cyclopropannulene: cycloprop-[8]annulene

Reacting (at 0 degrees C) a mixture of CH2Cl2 and monobromo[8]annulene (C8H7Br) with potassium tert-butoxide in hexamethylphosphoramide (HMPA) and following with exposure to potassium metal led to the formation of the anion radical of an HMPA-[6.1.0]bicyclononatetraene condensation product, in which two HMPA fragments are geminal and attached to the number 9 carbon. When the reaction sequence is carried out in THF, the dianion of cycloprop[8]annulene is predominantly formed. Neutral cycloprop[8]annulene can be isolated via the I2 oxidation of the THF solution. The NMR analysis reveals that the eight-membered ring is nearly planar, and the three-membered ring is more like a dimethylenecyclopropane than it is like a cyclopropene. Further, the chemical shifts due to the protons on the eight-membered ring are nearly 2 ppm further upfield than are those for [8]annulene itself, suggesting a paratropic ring current.