Analytical derivation of the Hückel “4n + 2 rule”

The “4n + 2 rule” is derived analytically at the level of the simple Hückel theory for neutral even-membered chains, their double ions, as well as cations and anions of the odd-membered chains, by determining the first order energetic effect of the ring closure. The topological background of the “4n + 2 rule” is also briefly discussed.     

Palladium-Catalyzed [3+2] and [2+2+2] Annulations of 4-Iodo-2-quinolones with Activated Alkynes through Selective C−H Activation

The palladium-catalyzed reaction of 4-iodo-2-quinolones with activated alkynes was investigated. Cyclopenta[de]quinoline-2(1 H)-ones and/or phenanthridine-6(5 H)-ones were obtained through [3+2] annulation involving aromatic C−H activation or [2+2+2] annulation involving vinylic C−H activation, respectively. Reasonable mechanisms for the formation of these annulation products have been proposed based on density functional theory calculations.     

Methano[10]annulene revisited: extended delocalization through conjugated polymers bearing larger Hückel aromatics

A comparative study of conjugated polymers derived from the two 10 pi electron circuits of naphthalene and methano[10]annulene is presented. The annulene pi topology allows for a greater degree of intrapolymer charge delocalization, a key structural parameter for enhancing the performance of organic semiconductors. Molecular design and synthesis based upon unusual aromatic cores will enable facile transport properties that would not ordinarily be realized under the 6 pi electron aromatic paradigm.     

[2+2] photodimerization of 1-aryl-4-pyridylbutadienes through cation–π interactions

Irradiation of 1-aryl-4-pyridylbutadienes in the presence of 1 equiv of HCl produced syn and anti head-to-tail dimers, among a number of possible dimers, whereas irradiation in the absence of HCl gave a complex mixture. This indicated that the acid serves as a catalyst for the regio- and stereoselective [2+2] photodimerization of 1-aryl-4-pyridylbutadienes through cation–π interactions between the pyridinium and aromatic rings. The produced synHT dimers underwent Cope rearrangement to produce cyclooctadienes, and they were in equilibrium at a ratio of 85:15 in CDCl₃.     

Aromaticity of the most stable adenine and purine tautomers in terms of Hückel's 4N+2 principle

Electron structures of the fused rings in 7H and 9H tautomers of purine and adenine follow the 4N + 2 rule; the values of pEDA, HOMA, NICS and FLU indices document their aromatic character. In the 1H and 3H tautomers, these rings contain five or seven π electrons, hence they do not follow this rule and consequently exhibit lower aromaticity. This also applies to the aromaticity of whole molecules.     

Base mediated synthesis of α-aminated aroyl/acetylnaphthalenes through [4+2] annulations

We have developed a base promoted simple, efficient and alternative approach for the synthesis of 4-amino-3-aroyl//heteroaroyl/acetyl-2-methylsulfanyl-naphthalene-1-carbonitriles by reaction of easily accessible 3,3-bis(methylthio)-1-aryl/heteroaryl/acetylprop-2-en-1-one and 2-cyanomethyl-benzonitrile. Reaction of 1-(2-halo/methoxy-phenyl)-3,3-bis(methylthio)prop-2-en-1-one and 2-cyanomethyl-benzonitrile under basic conditions also afforded 6-(methylthio)-7-oxo-7,12-dihydrobenzo[c]acridine-5-carbonitrile along with usual product. Structure of the synthesized product has been confirmed by single X-ray crystallography.     

Synthesis and structure of tetra-p-tolylantimony complexes [(4-MeC6H4)4Sb] 2 + [Hg2I6]2−, [(4-MeC6H4)4Sb] 2 + [HgI4]2−, [(4-MeC6H4)4Sb] 3 + [Sb3I12]2−, and [(4-MeC6H4)4Sb]+[ReO4]−

Complexes [(4-MeC₆H₄)₄Sb] ₂ ⁺ [Hg₂I₆]^2? (I), [(4-MeC₆H₄)₄Sb] ₂ ⁺ [HgI₄]^2? (II), [(4-MeC₆H₄)₄Sb] ₃ ⁺ [Sb₃I₁₂]^2? (III), were synthesized by reactions of tetra-p-tolylantimony iodide with mercury iodide and antimony iodide, respectively. Tetra-p-tolylantimony perrhenate [(4-MeC₆H₄)₄Sb]⁺[ReO₄]^? (IV) was prepared from tetra-p-tolylantimony chloride and sodium perrhenate in acetone. Crystal structures of complexes I, II, and IV were determined by X-ray crystallography. Mercury and rhenium atoms have tetrahedral coordinations in these complexes. The Hg-I and Re-O distances in the structures of I, II, and IV vary within 2.7719(13)–2.7908(12)Å, 2.7028(3)–2.9163(3) Å, and 1.693(3)–1.744(3) Å, respectively. Antimony atoms in two crystallographically independent trinuclear centrosymmetric [Sb₃I₁₂]^2? anions of complex III have an octahedral environment. Each terminal SbI₃ fragment (Sb-I_t, 2.8265(9)–2.8333(10)Å) is bound to the central atom through tree bridging iodine atoms (Sb(2)-I_br, 3.2275(9)–3.3620(10)Å). The distances between the central Sb atom and bridging iodine atoms are much shorter (Sb(1)-I_br, 3.0153(6)–3.0316(6) Å; Sb(3)-I_br, 2.9926(6)–3.0074(6) Å).     

Synthesis and structure of antimony complexes [Ph3AmP] 2 + [Sb2I8 · 2DMSO]2−, [Ph3PrP] 2 + [Sb2I8 · C4H8O2]2−, and [(HOCH2CH2)3NH] 4 + [Sb4I16]4−

The reaction of equimolar amounts of triphenylamyl- and triphenylpropylphosphonium iodides and triethanolammonium iodide with antimony iodide in dimethyl sulfoxide, dioxane, or acetone gave complexes [Ph₃AmP] ₂ ⁺ [Sb₂I₈ · 2DMSO]^2?, [Ph₃PrP] ₂ ⁺ [Sb₂I₈ · C₄H₈O₂]^2?, and [(HOCH₂CH₂)₃NH] ₄ ⁺ [Sb₄I₁₆]^4?, the structure of which was established by X-ray diffraction analysis. The cations of all complexes have slightly distorted tetrahedral structure, and the antimony atoms in the anions are hexacoordinated. The crystals of the complexes have intra- and intermolecular contacts, which form the structure.     

Theoretical study on conformation and electronic state of Hückel-aromatic multiply N-confused [26]hexaphyrins

Conformations and electronic states of Hückel-aromatic regular, singly, doubly, and triply N-confused [26]hexaphyrins were investigated using density functional theory (DFT) calculations. A comparison of the molecular energies of 754 structures in all revealed that the most stable conformers depend on the degree of confusion, where ring strain and intramolecular hydrogen bonding would play a critical role. Consequently, regular and singly N-confused hexaphyrins prefer a dumbbell conformation, doubly N-confused hexaphyrin prefers a rectangular conformation, and triply N-confused hexaphyrin prefers a triangular conformation. Introduction of N-confused pyrrole rings into the hexaphyrin framework causes narrower HOMO-LUMO energy gaps, while it does not affect the NICS values or aromaticity significantly. The steric repulsion imposed by meso-aryl substituents largely affects the relative energies among the conformers.     

Double-tandem [4π+2π]·[2π+2π]·[4π+2π]·[2π+2π] synthetic sequence with photoprotolytic oxametathesis and photoepoxidation in the chromone series

Chromones are introduced into a double-tandem [4(π)+2(π)]·[2(π)+2(π)]·[4(π)+2(π)]·[2(π)+2(π)] synthetic sequence, culminating in photoprotolytic oxametathesis, which leads to an expeditious growth of molecular complexity over a few experimentally simple steps. The overall reaction can potentially be utilized in diversity-oriented synthesis, as it allows for three or more diversity inputs furnishing novel unique polycyclic scaffolds decorated with a variety of functionalities and aromatic/heterocyclic pendants. The polycyclic alkenes, resulting from the oxametathesis step, were found to undergo efficient and clean photoinduced epoxidation when irradiated in the presence of molecular oxygen.     

Synthesis and structures of mercury and cadmium complexes: [Ph4Sb] 2 + [Hg2I6]2−·Ph2Hg, [Ph4Sb] 2 + [E2I6]2− (E = Hg, Cd), and [Ph4Sb] 2 + [Hg4I10]2−

The reaction of pentaphenylantimony with mercury iodide affords the ionic complex [Ph₄Sb] ₂ ⁺ [Hg₂I₆]^2?·Ph₂Hg (I). The [Ph₄Sb] ₂ ⁺ [Hg₂I₆]^2? (II) and [Ph₄Sb] ₂ ⁺ [Cd₂I₆]^2? (III) complexes are synthesized from tetraphenylantimony iodide and mercury and cadmium iodides. The [Ph₄Sb] ₂ ⁺ [Hg₄I₁₀]^2? complex (IV) is prepared from tetraphenylantimony 2,4-dimethylbenzenesulfonate and mercury iodide. According to the X-ray diffraction data, the Sb atom in the [Ph₄Sb]⁺ cations of complex I has virtually ideal tetrahedral coordination (the CSbC angles are 108.09°–109.64°). In the central square fragment Hg₂I₂ of the [Hg₂I₆]^2? anion, the Hg-I_br bond lengths are 2.825 and 3.075 Å, and the terminal iodine atoms are more strongly bonded to the mercury atoms (Hg-I_term 2.691 and 2.700 Å). The [Cd₂I₆]^2? anion in complex III has a similar structure (the Cd-I_bridg and Cd-I_term distances are 2.865, 2.872 and 2.723, 2.748 Å, respectively). The anions in complex IV are joined by I…Hg (3.651 Å) and I…I (4.058 Å) interactions into an infinite dimeric network.     

Syntheses and crystal structures of two Cd(II) coordination polymers: one-dimensional chain [Cd(C4H6N2)2(C4H2O4)(H2O)2] n and two-dimensional sheet [Cd(C4H6N2)(H2O)(C4H4O4)] n · n H2O

Two new Cd(II) coordination polymers, [Cd(C₄H₆N₂)₂(C₄H₂O₄)(H₂O)₂] _n (1) (where C₄H₆N₂?=?2-methylimidazole, C₄H₂O₄?=?fumarate), and [Cd(C₄H₆N₂)(H₂O)(C₄H₄O₄)] _n ?·?nH₂O (2), (where C₄H₄O₄?=?succinates), have been prepared and structurally characterized by single crystal X-ray diffraction. Complex 1 crystallizes in the triclinic space group P 1 in a one-dimensional chain structure, in which carboxy is monodentate; a three-dimensional supermolecular network structure was formed through hydrogen bonding. In complex 2, the coordination geometry of the Cd atoms is a pentagonal bipyramid, and a two-dimensional sheet is formed though carboxyl group bridging. In 1 and 2, IR spectra indicate the presence of bridging carboxyl groups, confirmed by structure analyses.     

Synthesis and structure of bismuth complexes [Ph3MeP] 2 + [BiI3.5Br1.5(C5H5N)]2− · C5H5N, [Ph4Bi] 4 + [Bi4I16]4− · 2Me2C=O, and [Ph3(iso-Am)P] 4 + [Bi8I28]4− · 2Me2C=O

Complexes [Ph₃MeP] ₂ ⁺ [BiI_3.5Br_1.5(C₅H₅N)]^2? · C₅H₅N(I), [Ph₄Bi] ₄ ⁺ [Bi₄I₁₆]^4? · 2Me₂C=O (II), and [Ph₃(iso-Am)P] ₄ ⁺ [Bi₈I₂₈]^4? · 2Me₂C=O (III) were synthesized by reactions of bismuth iodide with triphenylmethylphosphonium bromide, triphenylbismuthonium sulfosalicylate, and triphenylisoamylphosphonium iodide, respectively. The crystal structures of complexes I–III were determined by X-ray crystallography. The complexes contain, in addition to cations and solvent molecules, mono-, tetra-, and octanuclear anions, in which bismuth atoms are in octahedral coordination.     

Synthesis and structure of bismuth-containing complexes [Ph3PMe] 2 + [BiI5]2− and [Ph3PMe] 2 + [BiI5 · C5H5N]2− · C5H5N

The complexes [Ph₃PMe] ₂ ⁺ [BiI₅]^2? (I) and [Ph₃PMe] ₂ ⁺ [BiI₅ · C ₅H₅N]^2? · C ₅H₅N (II) were synthesized by the reaction of bismuth triiodide with triphenylmethylphosphonium iodide, and their structures were determined by X-ray diffraction analysis. The P atom in cation I has slightly distorted tetragonal coordination polyhedron (the CPC angles 109.42(4)° and 109.52(4)°, the bond lengths P-C_Ph 1.779(2), P-C_Me 1.793(1) Å. The Bi atom in the anion of complex I has an ideal trigonal-bipyramidal coordination polyhedron (Bi-I_eq 3.0031(4), Bi-I_eq 3.0485(5) Å). The crystal of complex II consists of the anions [BiI₅ · C ₅H₅N]^2?, solvated pyridine molecules, and two types of crystallographically independent tetrahedral triphenylmethylphosphonium cations (the angles CPC 106.9(1)°–111.7(1)°, the distances P-C_Ph 1.785(3)–1.792(3), P-C_Me 1.793(3), 1.786(3) Å). The Bi atoms in the anion of complex II have a distorted octahedral coordination polyhedron (Bi-I 3.0878(4)–3.1240(3), Bi-N(1) 2.628(3) Å).     

Intermolecular [4+3] Cycloaddition of Cyclic Oxyallyl

The[4+3]cycloaddihonreachonofatlyliCcationsanddienesisavodemeIhalfortheconstwhonofseven-memberedrings1.AkCyvariantofemPlOyingacyclicoxyalll,i.e.,anoxyallylembeinring,wouldPrOvidCaconvenientroutetofunctiotaledmdri-eddsyClesandheteIDCycles.Inaddihon,theketobridgeinthecycloadductwouldbeusefulnotonlyinProvthegasultablefUnchonalityforfurtherebohonbutalsoinrigmpingthefiechemedium-edring.Chaandhisco-workershaveemployedthesaPPrOaChtOthesynthesisofnandProductS2.AtpesenLonlyafewexamplesofthisre…     

The unusual stability of [NpO2Cl4]2−: Synthesis and characterisation of [NpO2(DPPMO2)2Cl]2[NpO2Cl4] and [Ph3PNH2]2[NpO2Cl4]

The [NpO₂(DPPMO₂)₂Cl][NpO₂Cl₄] complex (where DPPMO₂ = bis(diphenylphosphino)methanedioxide) contains the linear neptunyl group, {NpO₂}²⁺, with two bidentate P=O donor ligands. Coordinating anion Cl^? fills the fifth equatorial coordination site yielding a complex of general formula [NpO₂(DPPMO₂)₂X]₂[Y] (1) (where X = Cl^? and Y = [NpO₂Cl₄]^2?. Reaction between our newly prepared neptunium starting material [NpO₂Cl₂(thf)]_n and phosphinimine ligand produced crystals of [Ph₃PNH₂]₂[NpO₂Cl₄] (2). Compounds 1 and 2 have been structurally characterised.     

炔烃与[Cp*Ru(H2O)(NBD)]BF4的[2+2+2]Diels-Alder反应

过渡金属催化的[2 2 2]环加成反应由于没有原子损失和较高的立体选择性,在合成不饱和多环化合物中已经被广泛应用[1].但一般反应时间较长,反应时常需要加热.我们发现金属有机化合物[Cp*Ru(H2O)(NBD)]BF4(Cp*是五甲基环戊二烯基,NBD是降冰片二烯)中的NBD与甲基苯基乙炔在室温就可发生[2 2 2]Diels-Alder反应[2].进一步研究发现,在室温下,炔烃PhC三CR(R=H,COOEt,Ph)和双炔烃HC三CC6H4C6H4C三CH与[Cp*Ru(H2O)-(NBD)]BF4中的NBD也能进行Diels-Alder反应,30 min即以较高产率生成[2 2 2]环加成产物.     

Intramolecular Benzyne–Phenolate [4+2] Cycloadditions

An intramolecular benzyne–phenolate [4+2] cycloaddition is reported. Benzyne precursors, having vicinal halogen-sulfonate functionalities, linked with a phenol(ate) by various tether groups undergo efficient intramolecular [4+2] cycloaddition by treatment with either Ph₃MgLi or nBuLi for halogen–metal exchange to form various benzobarrelenes.