Intermediacy of cyclobutylidene in photochemical methylenecyclopropane rearrangement

Methylenecyclopropane 1 undergoes photochemical rearrangement to 2. Intervention of cyclobutylidene 3 explains not only the rearrangement but also newly obtained products such as cyclobutene 4 and cyclobutylidenecyclobutane 6. Experiments designed to generate cyclobutylidene 3 independently have provided some support for the intermediacy of 3.     

New facets in the photochemistry and thermal reaction of 2,2-diphenylmethylenecyclopropane

Photochemistry and thermal reaction of 2,2-diphenylmethylenecyclopropane 1a have been reinvestigated to make their mechanistic refinement. A new finding in the photochemistry of 1a is the detection and isolation of cyclobutene 7. While fragmentation and 1,3-carbon (C) shift is responsible for previously reported photoproducts, 1,1-diphenylethylene 3 and diphenylmethylenecyclopropane 2a, respectively, a new pathway is required to explain the formation of cyclobutene 7. A mechanism involving the 1,2-C shift (Scheme 3, arrow b) followed by 1,2-hydrogen (H) shift is proposed. In the thermal reaction of 1a, on the other hand, a trimethylenemethane type of species is shown to be a common intermediate for degeneracy, rearrangement from 1a to 2a, and formation of indene 5. In the photochemistry of 1a, intervention of cyclobutylidene 8 is strongly supported by circumstantial evidences provided by steady-state and laser flash photolytic investigations. Further experiments designed to independently generate cyclobutylidene 8 showed the methylenecyclopropane/cyclobutene branching ratio (1a/7) to be in the range between 0 and 1.7, which is much lower than the value of 4.0 for parent cyclobutylidene. Nevertheless, the relative efficiency of 1,2-shift pathway to generate 8 is shown to be as high as 17–47% compared to 1,3-C shift to give 2a at the early photochemical stage of 1a.     

Trimer–dimer equilibrium studies of alkylaluminum alkoxides

The aluminum alkoxides [MeClAlOEt]₃ (1), [Et₂AlOMe]₃ (2), [Me₂AlOEt]₃ (3), and [EtClAlOEt]₃ (4) were investigated by ¹H NMR spectroscopy to study the o-dichlorobenzene solution equilibrium: 2 [R₂AlOR′]₃⇌3 [R₂AlOR′]₂. The complexes are shown to exist primarily as trimers at room temperature, but increasing concentrations of the dimeric form are observed at higher temperatures. Equilibrium constants, ΔH, and ΔS were determined for the trimer–dimer equilibrium. Values of ΔH for the conversion of 2 moles of trimer are 63(4), 78(1), 85.0(8), and 99(6) kJ for 1, 2, 3, and 4, respectively. The corresponding values of ΔS are 142(7), 184(3), 218(2), and 265(17) J/K, respectively. Thermodynamic parameters are compared with those reported for [Me₂AlOPrⁿ]₃ and [Me₂AlOPh]₃. The characterization of [EtClAlOMe]₃ is also reported.     

Reactions of carbonyl clusters with potentially tridentate thioethers: Crystal and molecular structures of [Os4(CO) 13([12]aneS3)] and [Ru6(CO)15(μ4-η2- CO)([12]aneS3)] [([12]aneS3) = {(CH2) 3S}3]

The reaction of [Os₃(CO)₁₂ with [12]aneS₃ ([12]aneS₃  {(CH₂)₃S}₃) in octane for 6 h, under reflux, led to isolation of two products [Os₃(CO)₁₁([12]aneS₃)] (1) and [Os₄(CO) ₁₃([12]aneS₃)] (2), while with [Ru₃(CO)₁₂] under similar conditions, in THF, a number of products were obtained, including [Ru₄(CO)₁₁([12]aneS₃)] (3), [Ru₅(CO)₁₃([12]aneS₃)] (4), and [Ru₆(CO)₁₆([12]aneS₃)] (5). An X-ray diffraction study of 2 shows that the macrocycle is coordinated to the ‘wingtips’ of an Os₄ butterfly through the two electron pairs on one sulphur atom, while in 5 all three sulphur atoms of the macrocycle coordinate to two of the Ru atoms in a spiked edge-bridged tetrahedral metal framework.     

Reaction of benzyne with cycloheptatriene preparation and thermolysis of some benzo(C9H10) hydrocarbons

The title reaction gave a 2+2 cycloadduct, 8,9-benzo-cis-bicyclo[5.2.0]nona-2,4,8-triene 7, together with ene product, 7-phenylcycloheptatriene. The structure of 7 was confirmed by catalytic reduction to give 8,9-benzo-cis-bicyclo[5.2.0]non-8-ene, which was also obtained in the reaction of benzyne with cycloheptene, and by reduction of the known 8,9-benzobicyclo[5.2.0]nona-1,8-diene. Other benzo(C₉H₁₀) hydrocarbons which have been synthesised are 7,8-benzobicyclo[4.2.1]nona-2,4,7-triene 5, 2,3-benzobicyclo[6.1.0]nona-2,4,6-triene 28 and 4,5-benzobicyclo[6.1.0]nona-2,4,6-triene 29. The thermolysis of 7, 28, 29 and of 3,4-benzo-exo-endo-tetracyclo[4.3.1.0^3,4.0^7,9]dec-3-en-10-one, 25, is described.     

Synthesis and spectral investigations of vanadium(IV/V) complexes derived from an ONS donor thiosemicarbazone ligand

Four oxovanadium and one dioxovanadium complex with 2-hydroxyacetophenone N(4)-phenylthiosemicarbazone (H₂L) which are represented as [VOLphen]·2H₂O (1), [VOLbipy] (2), [VOLdmbipy] (3), [VOL]₂ (4) and [VO₂HL]·CH₃OH (5) have been synthesized and characterized by elemental analyses, electronic, infrared and EPR spectral techniques. In all the complexes 1–4 the ligand coordinates through phenolic oxygen, azomethine nitrogen and thiolate sulfur. But in complex [VO₂HL]·CH₃OH, coordination takes place in thione form instead of thiolate sulfur. All the complexes except [VO₂HL]·CH₃OH are EPR active due to the presence of an unpaired electron. In frozen DMF at 77 K, all the oxovanadium(IV) complexes show axial anisotropy with two sets of eight line patterns.     

Zirconium complexes of the tridentate bis(aryloxide)-N-heterocyclic-carbene ligand: Chloride and alkyl functionalized derivatives

The disodium salt of a bis(aryloxide)-N-heterocyclic-carbene dianionic ligand, Na₂[L], was prepared by reaction of 1,3-bis(4,6-di-tert-butyl-2-hydroxybenzyl)imidazolium bromide [H₃L]Br with 3 equiv. of NaN(SiMe₃)₂. Reaction of ZrCl₄(thf)₂ with 1 equiv. of Na₂[L] gave a mixture of [L]ZrCl₂(thf) (1) and [L]₂Zr (2). When the amount of Na₂[L] was increased to 2 equiv., the bis(bis(aryloxide)-N-heterocyclic-carbene) complex 2 was obtained in good yield. The dichloro complex 1 is a precursor to organometallic derivatives, and treatment with PhCH₂MgCl or Me₃SiCH₂Li yielded [L]ZrR₂ [R = CH₂Ph (3), CH₂SiMe₃ (4)]. The disodium salt of the ligand Na₂[L] is unstable and undergoes 1,2-benzyl migration, whereas zirconium complexes of the [L]²⁻ ligand are found to be thermally stable in solid and solution. The X-ray crystal structures of 1, 2, and 3 are described.     

A new route to alkenylcyclobutenes

Reaction of titanium cyclobutylidene complexes, prepared by the desulfurizative titanation of 1,1-bis(phenylthio)cyclobutanes with Cp₂Ti[P(OEt)₃]₂, with alkynes gave 1-(alk-1-enyl)cyclobutenes.     

Reactions of dispiro[2.0.2.2]oct-7-ene. Electrophilic and free radical additions

Dispiro[2.0.2.2]oct-7-ene 1 was synthesized by debrominatioa of cis- and trans-7,8-dibromodispiro[2.0.2.2]octane 3a with LAH and by dechlorination of cis- and trans-7,8-dichlorodispiro[2.0.2.2]octane 3b with magnesium. Stepwise electrophilic additions to 1 of HBr, HI, Br₂ and Cl₂ were studied. The major products (and yields) from these reactions were: 7-bromodispiro[2.0.2.2]octane 2a (43%), 4-iodo-4,5-ethanospiro[2,3]hexane 4b (ca. 50%); trans-3a (40%); and cis-3b (20%). Free-radical addition of hydrogen bromide to 1 gave an 80% yield of 7-bromodispiro[2.0.2.2]octane 2a. At ?10°, hydroboration-oxidation of 1 was found to give mainly 7-hydroxydispiro[2.0.2.2]octane 2a in ca. 90% yield; at 25°, near equal amounts of 2c and 4-(2-hydroxyethyl) spiro[2.3]hex-4-ene 14 were obtained.     

Synthesis of novel calix[4]arenes containing organosilicon groups

Metalation of (RSiMe₂)₃CH (1a R = H, 1b R = Me, 1c R = Ph) with lithium diisopropylamide (LDA) or methyllithium in THF gave organolithium reagents (RSiMe₂)₃CLi, which reacted with the formylated calixarene (2), to give the corresponding 5,17-bis[2,2-bis(organosilyl)-1-ethenyl]-25,26,27,28-tetrapropoxycalix[4]arenes (3a, 3b and 3c) via the Peterson olefination. The compounds (RSiMe₂)₃CLi were treated with 25,26,27,28-tetrakis(4-bromobutoxy)calix[4]arene (4) to give 25,26,27,28-tetrakis[4-(tris(dimethylsilyl)methyl)butoxy] calix[4]arene (5a) and 25,26,27,28-tetrakis[4-(tris(trimethylsilyl)methyl)butoxy] calix[4]arene (5b) via nucleophilic substitution reactions. However the compound 25,26,27,28-tetrakis[4-(tris(dimethylphenylsilyl)methyl)butoxy] calix[4]arene (5c) was not obtained, presumably because (PhSiMe₂)₃C- is highly sterically hindered and the reactivity of its derivatives is low. The compound 5a has potential as a core for dendrimers.     

The synthesis of [15]annulenone 4,7:10,13-dioxides and aromatic 4,7:10,13-dioxido[15]annulenium cations : Novel 14]gp ‘odd’ annulene systems

2,15 - Dimethoxycarbonyl - [15]annulenone 4,7:10,13 - dioxide (14) has been prepared by the condensation of cis -α,β -bis(5 - formyl - 2 - furyl)ethy]ene (13) with dimethyl acetonedicarboxylate. Treatment of 14 with conc H₂SO₄ led to 4,7:10,13-dioxido[15]annulenone 2,15-dicarboxylic acid anhydride (17), which was subsequently converted to the corresponding dicarboxylic acid (18) by dilute KOH. Decarboxylation of 18 gave rise to two isomeric [15]annulenone 4,7:10,13 - dioxides, i.e., the tri-cis isomer (7) and the mono - trans - di - cis isomer (8).Regarding to the ring current effects, the proton chemical shifts of these [15]annulenones were compared with those of a reference model, 4,7:10,13 - dioxido - cyclopentadecaheptaene (2.4.6.8.10.12.14) (3). Both of the parent [15]annulenones (7 and 8) have been interpreted as nondiatropic, while the anhydride (17) has been shown to be diatropic, sustaining an induced diamagnetic ring current. The enforced planarity and symmetrical geometry of the anhydride have been discussed. As expected, when 7, 8, 14, 17 and 18 were dissolved in CF₃COOH or conc H₂SO₄, completely delocalized [15]annulenium cations were produced, all of which proved to be diatropic. Three possible geometrical isomers of these 14π cations were established experimentally.     

A disulfide-bridged manganese carbonyl anion: synthesis,structure and reactivity of [Mn3(CO)10(μ3-S2)2]−

The reduction of Mn₂(CO)₇(μ-S₂), (1) with sodium amalgam in THF provided the new monoanion [Mn₃(CO)₁₀(μ₃-S₂)₂]⁻, (3) isolated in low yield as the [Ph₃PMe] salt. The reaction of Mn₄(CO)₁₅(μ₃-S₂)(μ₄-S₂), (2) with [Ph₃PMe]I provided the same salt [Ph₃PMe] [3] in a good yield, 68%. Anion 3 reacts [CpFe(CO)₂(acetone)]BF₄ to yield the neutral mixed metal complex CpFeMn₃(CO)₁₂(μ₃-S₂)(μ₄-S₂), (4). The structures of [Ph₃PMe] [3] and 4 were determined by single crystal X-ray diffraction analyses. The core of the structure of 3 consists of two [Mn(CO)₃] groups bridged by two disulfido ligands in a μ₂–η² fashion with an additional [Mn(CO)₄] group that bridges the two disulfido ligands. The CpFe(CO)₂ group in 4 is bonded to a sulfur atom of one of the two disulfido ligands of the anionic grouping of 3.     

Synthesis,structure, and conformation of terphenylene-derived azacalix[4]aromatics

Several novel azacalix[4]aromatics constituting terphenylene units have been synthesized via sequential nucleophilic aromatic substitution reactions of 5′-t-butyl-(1,1′:3′,1″-terphenyl)-3,3″-diamine 9 and 5′-t-butyl-(1,1′:3′,1″-terphenyl)– 4,4″-diamine 11 with 1,5-difluoro-2,4-dinitrobenzene and cyanuric chloride, respectively. The bridging –NH– functions of the tetra-nitro substituted azacalix[2]arene[2]terphenylenes 1 and 2 have been transformed to the corresponding –N(CH₃)– bridged azacalix[2]arene[2]terphenylenes 3 and 4 via N-alkylation. Single crystal X-ray analysis revealed that the terphenyl-3,3″-diamine derived azacalix[2]terphenylene[2]triazine 5 adopts a distorted chair conformation in the solid state, and the terphenyl-4,4″-diamine derived azacalix[2]terphenylene[2]triazine 6 was found to adopt a 1,3-alternate conformation.     

Synthesis of medium-ring bicyclic diamines by the alkylation and cleavage of cyclic amidines

1,6-Diazabicyclo[4.3.3]dodecane (7), 1,6-diazabicyclo[4.3.2]undecane (8) and 1,8-diazabicyclo[6.3.3]tridecane (9) have been made by reduction of tricyclic α-aminoammonium salts with LiAlH₄; the protonation and oxidation of 8 and 9 are discussed.     

In situ synthesis of Ag nanoparticles in aminocalix[4]arene multilayers

The layer-by-layer (LbL) assembled thin films containing tetraamino-thiacalix[4]arenes (1) and tetraamino-calix[4]arenes (2) were used as nanoreactor to synthesize in situ Ag nanoparticles (Ag NPs). UV–vis spectra and AFM images demonstrate that Ag NPs are included in the (1/Ag NPs)_n and (2/Ag NPs)_n multilayer films. The silver ions are absorbed through cation–π interaction and calix[4]arene-metal ion coordination interaction and are reduced into Ag NPs by calix[4]arenes. TEM images indicated that Ag NPs within aminocalix[4]arene multilayers were highly dispersed and uniform. Moreover, the mean size of Ag NPs is smaller than 10 nm.     

Energy transfer or electron transfer?—DFT study on the mechanism of [2+2] cycloadditions induced by visible light photocatalysts

The intramolecular [2+2] cycloaddition of 1,3-dienes under visible light irradiation investigated by Yoon and his co-workers shows remarkably high yield and stereoselective differences under different photocatalysts. The reaction was speculated to be induced by energy transfer. However, the origin for these phenomena is still unclear. In this scene, the detailed mechanism for the [2+2] cycloaddition of 1,3-dienes under visible light has been investigated using density functional theory B3LYP and TPSSTPSS methods. The result shows that the reaction not only can be induced by energy transfer between photocatalysts and reactants, but also can be induced by electron transfer between them. The [2+2] cycloaddition induced by energy transfer is carried out along the potential energy surface (PES) of triplet excited states (T₁) firstly, and then goes back to the singlet ground state (S₀) via MECPs (minimum energy crossing points) between the PESs of the S₀ and T₁ states, forming the product in the S₀ state. The [2+2] reaction induced by electron transfer proceeds along the doublet state PES of the cation radical reactant and the neutral four-membered ring product could be obtained by electron transfer from the corresponding reactant or reduced photocatalyst. The origin of stereoselectivity of the [2+2] reaction is attributed to the reaction mechanism difference under different photocatalysts.     

Synthesis and structure of a chiral areno-bridged [2.4]metacyclophane

The reductive coupling reaction of 1,4-bis(3-acetyl-5-tert-butyl-2-methoxyphenyl)butane 3 was carried out using TiCl₄-Zn in pyridine followed by a McMurry coupling reaction to afford the compounds anti and syn 1,2-dimethyl[2.4]MCP-1-ene 4. Bromination of 4 with BTMA-Br₃ in dry CH₂Cl₂ afforded the interesting compound 1,2-bis-(bromomethyl)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-1-ene 6 and consecutive debromination with Zn and AcOH in CH₂Cl₂ solution afforded the stable solid 5,15-di-tert-butyl-8,18-dimethoxy-1,2-dimethylene[2.4]MCP 7 in 89% yield. Compound 7 was conveniently employed in a Diels–Alder reaction with dimethyl acetylenedicarboxylate (DMAD) to provide 2-(3′,6′-dihydrobenzo)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-4′,5′-dimethylcarboxylate 8 in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiral areno-bridged compound [2.4]MCP 9 by aromatization. The chirality of the two conformers was characterized by circular dichroism (CD) spectra of the separated enantiomer which are perfect mirror images of each other.     

Clip[5]arenes: A new family of molecular clips

Here we report the design and syntheses of two new triptycene-based rigid acyclic C-shaped hosts, clip[5]arenes C[5]OH and C[5]ME, and the strong host–guest complexation between C[5]OH and an electron-poor bipyridinium salt, paraquat G. The K_a value for the host–guest complex C[5]OH???G was calculated to be (1.09?±?0.36)??×??10⁵?M^?1 in acetone by using a non-linear curve-fitting method based on the UV–vis absorption titration experiments. Furthermore, based on this new host–guest recognition motif, a novel pseudopolyrotaxane-like supramolecular structure was constructed with C[5]OH threaded on polyviologen polymer VP-10.     

Die erste fluormethylidin-verbrückte molybdän-cluster-verbindung: darstellung und struktur von [(C5H5)3(CO)6Mo3(μ3-CF)]

Treatment of [Cp(CO)₃Mo]⁻ with ClCOCF₂COCl gave [Cp(CO)₃MoCOCF₂COMo(CO)₃Cp] (1), which, by loss of CO gave [Cp(CO)₃MoCOCF₂Mo(CO)₃Cp] (2). Further loss of CO moieties from 2 resulted in a mixture of different molybdenum complexes. The trinuclear complex [Cp₃(CO)₆Mo₃(μ₃-CF)] (3) was considered the most interesting one. The crystal structure of 3 is presented. The compound appears as two crystallographical independent molecules of identical structure, which crystallize in two enantiomeric forms.     

Reaction of ruthenium complexes containing heterocyclic thiazine–thione ligand

Treatment of the ruthenium complex [Ru]---

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(3, [Ru]=Cp(dppe)Ru) containing a heterocyclic [1,3]-thiazine-4-thione six-membered-ring ligand with various organic halides results in alkylation at the thione sulfur terminus of the ligand to yield [Ru]---

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][X] (4a, R=CN, X=I; 4b, R=Ph, X=Br; 4c, R=CH=CH₂, X=I, 4d, R=p-C₆H₄CF₃, X=Br). Similarly the reaction of 3 with HgCl₂ at room temperature affords [Ru]---

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][Cl] (5). Transformation of 5 to the cationic vinylidene complex {[Ru]=C=C(Ph)C(O)NHPh}₂[Hg₂Cl₆] (6) readily occurred in the air. The structures of 4c and 6 are determined by single crystal X-ray diffraction analysis.