Four-membered Cycle Research Articles

Competitive Processes of Energy Transfer and Opening of the Four-Membered Cycle in Cyclobutanes Formed in [2+2] Photocycloaddition Reaction of Bis(styrylbenzoquinoline) Dyads

Competitive Processes of Energy Transfer and Opening of the Four-Membered Cycle in Cyclobutanes Formed in [2+2] Photocycloaddition Reaction of Bis(styrylbenzoquinoline) Dyads

Speciation Study on O-Phosphorylethanolamine and O-Phosphorylcholine: Acid-Base Behavior and Mg2+ Interaction.

In the present study, the acid–base behavior of compounds constituting the headgroups of biomembranes, O-phosphorylethanolamine (PEA), and O-phosphorylcholine (PPC) was investigated by potentiometric titrations in NaCl aqueous solutions at different temperatures (15 ≤ t/°C ≤ 37) and ionic strength (0.15 ≤ I/mol L−1 ≤ 1) values. The complexation properties and the speciation of these ligands with Mg2+ were defined under different temperatures (15 ≤ t/°C ≤ 37) and I = 0.15 mol L−1. The results evidenced the formation of three species for PEA, namely, MLH2, MLH, and ML and two species for PPC, namely, MLH and ML. 1H-NMR titrations were performed on solutions containing ligand and metal–ligand solutions at t = 25°C and I = 0.15 mol L−1. The estimated values of ligand protonation and complex formation constants and the speciation model are in accordance with the potentiometric data. The enthalpy changes were also determined at t = 25°C and I = 0.15 mol L−1 by the dependence of formation constants on the temperature, confirming the electrostatic nature of the interactions. Matrix-assisted laser desorption mass spectrometry (MALDI-MS) was applied for the characterization of Mg2+-L systems (L = PEA or PCC). MS/MS spectra of free ligands and of Mg2+-L species were obtained. The observed fragmentation patterns of both Mg2+-L systems allowed elucidating the interaction mechanism that occurs via the phosphate group generating a four-membered cycle.

Consecutive and Selective Double Methylene Insertion of Lithium Carbenoids to Isothiocyanates: A Direct Assembly of Four-Membered Sulfur-Containing Cycles.

A formal CH2−CH2 homologation conducted with C1 carbenoids on a carbon electrophile for the obtainment of a four‐membered cycle is reported. The logic proposes the consecutive delivery of two single nucleophilic CH2 units to an isothiocyanate—as competent electrophilic partner—resulting in the assembling of a rare imino‐thietane cluster. The single synthetic operation procedure documents genuine chemocontrol, as indicated by the tolerance to various reactive elements decorating the starting materials. Significantly, the double homologation protocol is accomplished directly on a carbon electrophile, thus not requiring the installation of heteroatom‐centered manifolds (e.g. boron).

Solid-State Photoinitiated Cycloaddition Reaction of 4,4′-(Ethene-1,2-diyl)bis(pyridinium) Dinitrate: Charge-Density Perspective on Initial Stage of the Reaction

Solid-state photoinitiated [2 + 2] cycloaddition reaction 2(H2bpe)(NO3)2 → (H4tpcb)(NO3)4 (bpe = 1,2-bis(pyrid-4-yl)ethylene; tpcb = 1,2,3,4-tetrakis(pyrid-4-yl)cyclobutane) was carried out in a single-crystal-to-single-crystal manner. The reaction product was characterized by means of X-ray diffraction and 1H NMR spectroscopy. Only the rctt-isomer of tpcb was found as the reaction product. Intermolecular interactions in a single crystal of (H2bpe)(NO3)2 were studied within the QTAIM approach. Although sum energy of strong and weak hydrogen bonds dominates in total packing energy, contribution of π…π stacking interactions to the packing energy is also prominent. At solid (H2bpe)(NO3)2, stacking of photoreactive H2bpe2+ cations is realized via N…C, C…C and C–H…C bonding, although no four-membered cycles formed by these bond paths was found in molecular graph representation. Reduced density gradient (RDG) surfaces and molecular Voronoi surfaces clearly demonstrate accumulation of charge density between olefin groups prone to take part in photoinitiated cycloaddition reactions. Good correlation between description of hydrogen bonding in terms of QTAIM and Voronoi approaches was demonstrated. The Voronoi approach confirmed that during the photoreaction the system of hydrogen bonds remained almost unchanged.

Carbonylation of Polyfluorobenzocyclobutenones in a SbF5 Medium

The carbonylation of perfluoro-2-R-benzocyclobutenones (R = F, CF3, C2F5, C6F5) in a CO-SbF5 system is accompanied by transformations of the four-membered cycle in the substrate to form polyfluorinated 1H-isochromene derivatives. The reaction of perfluoro-2-R-benzocyclobutenes (R = F, CF3, C2F5) with (CF3CO)2O or CF3COOH in a SbF5 medium in a sealed ampule involves formation of polyfluorobenzocyclobutenones and their carbonylation under the reaction conditions.

Tightly Bound Double-Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells.

A series of novel highly soluble double-caged [60]fullerene derivatives were prepared by means of lithium-salt-assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four-membered cycle and a pyrrolizidine bridge with an ester function CO2 R (R=n-decyl, n-octadecyl, benzyl, and n-butyl; compounds 1 a-d, respectively), as demonstrated by NMR spectroscopy and X-ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one-electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone-electron pair. Owing to charge delocalization over both carbon cages, compounds 1 a-d are characterized by upshifted energies of frontier molecular orbitals, a narrowed bandgap, and reduced electron-transfer reorganization energy relative to pristine C60 . Neat thin films of the n-decyl compound 1 a demonstrated electron mobility of (1.3±0.4)×10-3 cm2 V-1 s-1 , which was comparable to phenyl-C61 -butyric acid methyl ester (PCBM) and thus potentially advantageous for organic solar cells (OSC). Application of 1 in OSC allowed a twofold increase in the power conversion efficiencies of as-cast poly(3-hexylthiophene-2,5-diyl) (P3HT)/1 devices relative to the as-cast P3HT/PCBM ones. This is attributed to the good solubility of 1 and their enhanced charge-transport properties - both intramolecular, owing to tightly linked fullerene cages, and intermolecular, owing to the large number of close contacts between the neighboring double-caged molecules. Test P3HT/1 OSCs demonstrated power-conversion efficiencies up to 2.6 % (1 a). Surprisingly low optimal content of double-caged fullerene acceptor 1 in the photoactive layer (≈30 wt %) favored better light harvesting and carrier transport owing to the greater content of P3HT and its higher degree of crystallinity.

Two Keggin compounds constructed from tri −/tetra-nuclear Cu clusters linked mono copper(II)-substituted phosphomolybdates

Two new compounds based on mono copper(II)-substituted phosphomolybdate, [Cu4(tea)6(H4PMo11CuO39)(PMo12O40)]2·33H2O (1) and [Cu3(tea)6(H2O)2(H2PMo11CuO39)2]2·30H2O (2) (tea =2- [1,2,4]triazol-4-yl-ethylamine), have been synthesized under hydrothermal conditions. Compound 1 owns tetra-nuclear clusters [Cu4(tea)6], linking a pair mono copper(II)-substituted and saturated Keggin anions to form a 2D structure. Compound 2 contains tri-nuclear clusters [Cu3(tea)6], fusing four mono copper(II)-substituted anions to construct a discrete four-membered cycle structure.

Theoretical study on the reaction mechanism of azacyclopropenylidene with azetidine: an insertion process

The mechanism of reaction between azacyclopropenylidene and azetidine has been systematically investigated employing the second-order Moller-Plesset perturbation theory (MP2) method to better understand the azacyclopropenylidene reactivity with azetidine four-membered cycle. Geometry optimization, vibrational analysis, and energy properties for the involved stationary points on the potential energy surface have been calculated. It was found that at the first step of this reaction, azacyclopropenylidene can insert into azetidine cycle at its C-N or C-C bond to form spiro intermediate IM. It was found that azacyclopropenylidene insertion into C-N bond is easier than into C-C bond. Through the ring-opening step at C-C bond of azacyclopropenylidene fragment, IM can transfer to product P1, which is named as pathway (1). On the other hand, through the H-transferred step and subsequent ring-opened step at C-N bond of azacyclopropenylidene fragment, IM can turn into product P2, which is named as pathway (2). From the thermodynamics viewpoint, P2 allene is the dominating product. From the kinetic viewpoint, the pathway (1) of formation to P1 is primary.

Crystal and molecular structure of the [Nd2(H2O)8(C6F5COO)6]·2H2O Compound

A compound with the composition Nd(C6F5COO)3· H2O (I) is prepared. Single crystals are grown, and their single crystal XRD analysis of the Nd2(H2O)8(C6F5COO)6]·2H2O (II) compound is performed. The crystals are triclinic: a = 7.693(2) A, b = 9.394(2) A, c = 18.203(4) A, α = 81.91(3)°, β = 84.41(3)°, γ = 88.97(3)°, Z = 1, dx = 2.223 g/cm3. The structure is composed of symmetrical molecules of the binuclear [Nd2(H2O)8(C6F5COO)6] complex and crystallization water molecules. The C6F5COO- ligands are monodentate and tridentate bridging- chelating, which results in a closure of two four-membered chelate cycles NdO2C and a four-membered metal cycle Nd2O2. The NdO9 polyhedron is a distorted one-capped tetragonal antiprism.

Luminescence properties of complexes Ln(Phen)(C6F5COO)3 (Ln = Tb, Eu) and Ln(C6F5COO)3 · nH2O (Ln = Tb, n = 2; Ln = Eu, n = 1). Structures of the [Tb2(H2O)8(C6F5COO)6] complex and its isomer in the supramolecular compound [Tb2(H2O)8(C6F5COO)6] · 2C6F5COOH

Complexes Ln(Phen)(C6F5COO)3 (Ln = Tb, Eu; Phen = 1,10-phenanthroline) (I, II) are synthesized. At 300 K these complexes and compounds Ln(C6F5COO)3 · nH2O (Ln = Tb, n = 2; Ln = Eu, n = 1) (III, VI) possess photoluminescence (bright in the case of I and II). In the spectrum of compound I the line at 545 nm (transition 5D4 → 7F5) is most intense, whereas in the spectrum of compound II the most intense is the line at 613 nm (transition 5D0 → 7F2). The replacement of Phen by water decreases the luminescence intensity. The compound [Tb2(H2O)8(C6F5COO)6] · 2C6F5COOH (IV) is synthesized. According to the X-ray diffraction data, in structure IV the molecules of the binuclear Tb(III) complex with the C6F5COOH molecules form a supramolecular ensemble due to hydrogen bonding. The C6F5COO− ligands perform the monodentate and bidentate bridging function, resulting in the opening of the eight-membered cycle Tb2C2O4. The TbO8 polyhedron is a distored tetragonal antiprism. The crystals of the binuclear complex [Tb2(H2O)8(C6F5COO)6] (V) are obtained in which the C6F5COO− ligands are monodentate and tridentate bridging cyclic, which results in the closure of two four-membered cycles TbO2C and one four-membered cycle Tb2O2. The TbO9 polyhedron is a distorted monocapped tetragonal antiprism.

Synthesis and crystal structure of 5-carbaphosphatranes containing a four-membered cycle

4,4-Bis(trifluoromethyl)-4,5-dihydro-2-phenylbenzo[e]- and 4,4-bis(trifluoromethyl)-4,5-dihydro-2-phenyl-(4’-chlorobenzo)[e]-1,3,2-dioxaphosphepin-5-ones react with hexafluoroacetone to form unusual propeller type structures – 3,3,10,10-tetrakis-(trifluoromethyl)-1-phenyl-6,7-benzo- and 3,3,10,10-tetrakis(trifluoromethyl)-1-phenyl-6,7-(4’-chlorobenzo)-2,4,8,9-tetraoxa-1-phosphatricyclo[3.3.2.01,5]decenes (5-carbaphosphatrane derivatives), the structure of which has been determined by NMR spectroscopy and single crystal X-ray diffraction analysis.

Nucleation of water vapor in microcracks on the surface of β-AgI aerosol particles: 1. The structure of nuclei

The precrystallization stage of nucleation of the condensed phase in wedge-shaped microcracks on the surface of β-AgI crystal at 260 K is studied by the Monte Carlo method. The microcrack field has a strong polarizing effect on the nucleus inducing the electrostatic forces of repulsion of molecules inside the nucleus and their attraction to the surface of microcrack walls. The growth of the nucleus in the microcrack passes through a stage of compaction, which is absent for the nuclei growing on the ideal surface. Microcrack surfaces stimulate, on the one hand, the formation of multilayered structures already at the earlier stage of clusterization and, on the other hand, the decomposition of the nucleus into unbound clusters whose main elements are six-and four-membered cycles. The β-AgI substrate shifts the equilibrium in small clusters from cubic to hexagonal symmetry. The analysis of the formation conditions of the known modifications of crystal and amorphous ice renders improbable the emergence of amorphous forms on the surface at the temperature studied; however, this allows us to consider the crystallization of nuclei to ice XI in the presence of microcracks as the probable event.

Synthesis and crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis[dichloro(thiocyanato)copper(II)

A new complex salt [4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis[dichloro(thiocyanato)copper(II)], [H2(Crypt-222)][CuCl2(SCN)]2, is synthesized and studied by X-ray diffraction analysis. The crystals are monoclinic (space group C2/c, a = 14.603 A, b = 8.330 A, c = 25.091 A, β = 100.76°, Z = 4). The structure is solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.047 for 2943 independent reflections (CAD-4 automated diffractometer, λMoK α radiation). The Cu2+ cations and Cl− and SCN− anions form infinite polymeric chains of spiro-conjugated alternating centrosymmetric four-membered CuCl2Cu cycles and eight-membered Cu(SCN)2Cu cycles through coordination bonds. The coordination polyhedron of the Cu2+ cation is a distorted trigonal bipyramid. The [H2(Crypt-222)]2+ dication contains trifurcate N+-(…O)3 bonds on axis 2.

A PtIII2Si2 Four-Membered Cycle and a Dinuclear Platinum Complex Bridged by a Cyclodisiloxane Ring

Thermolysis of an equilibrium mixture of {1,2-C6H4(SiMe2)(SiH2)}Pt(dmpe) (3; dmpe = 1,2-bis(dimethylphosphino)ethane) and its dimer 4 afforded a novel dinuclear complex consisting of a Pt2Si2 four-membered cycle with formal PtIII centers as well as a small amount of an unexpected dinuclear PtII complex bridged by a cyclodisiloxane ring.

Coupling characteristics and proton transfer mechanisms of guanine–Na + monohydrate

The coupling characteristics and the proton transfer mechanisms of guanine–Na + monohydrate are determined in this investigation after the implementation of the geometry optimization and the harmonic vibrational frequency calculations. There are two elementary coupling modes: the interaction of monohydrated sodium ion with two heteroatoms which form a ringed coupling, and hydrogen-bond involved coupling mode. Two potential reaction pathways, coupling mode and hydration have been taken into account, and the accurate values of binding energy are corrected for basis set superposition error (BSSE) and zero-point vibrational energy (ZPVE). Relative energies of the hydrated guanine–sodium ion complexes indicate that the ringed-coupling complexes are predominant geometries with much lower energies. Monohydrated sodium ion coupling with O6 and N7 generates the most stable geometry with a five-member cycle. Sodium ion plays an important role in the tautomerization for guanine–sodium ion complexes. This investigation indicates that the stable cation-π complexes cannot be optimized for guanine–sodium ion monohydrate. Amino-involved coupling often gives rise to a twisted four-membered cycle with unrealistic distribution of positive charge and higher energies. The rotation of amino group is likely to lead to the redistribution of the base pair hydration bonding. Effective distribution of the positive charge is an important factor in the stabilization of biological systems and binding energies for the monohydrated guanine–sodium ion complexes. The enolic coupling complex has the higher energy than the keto type due to the hindrance for the positive charge.

Reaction Paths of the [2 + 2] Cycloaddition of XCY Molecules (X, Y = S or O or CH2). Ab Initio Study

The reaction paths of [2+2] cycloaddition of the X=C=Y cumulenes were modeled at the MP2/aug-cc-pVDZ level. Cycloadditions of allene and CO2, CS2, or OCS lead in part to the same four-membered products as dimerizations of either ketene or thioketene or addition of ketene and thioketene, respectively. All the reactions studied are concerted and mostly asynchronous. The majority of the allene cycloadditions studied are endoergic and proceed with much higher activation barriers than do the alternative (thio)ketene additions. In comparison with the energy of the substrates, the four-membered cycles incorporating S-atoms are stabilized more than the analogous structures with O-atoms built into the rings. There are also some products that are thermodynamically disfavored, yet seem to be obtainable thanks to a relatively low barrier of the reaction. The AIM analysis of the electron density distribution in the transition state structures allowed distinguishing pericyclic from pseudopericyclic and nonplanar-pseudopericyclic types of reaction.

POLYCYCLES AND CAGES IN MOLECULAR ALUMO-POLYSILOXANES—(Ph2SiO)8[Al(O)OH]4 Used as a Supramolecular Target and “Auto-Condensation” Within the Molecule

In this preliminary review the reaction of [Ph2SiO]8[AlO(OH)]4 toward 1,3-diaminopropane and hexamethyldisilazane is discussed in view of supramolecular chemistry and access to structural transformations of the original polycycle. Two distinct adducts may be isolated in the first case: [Ph2SiO]8[AlO(OH)]4· 3H2N-CH2CH2CH2-NH2 and [Ph2SiO]8[AlO(OH)]4· 2H2N-CH2CH2CH2-NH2. Whereas in the 1:3 adduct the four protic hydrogen atoms of the inner Al4(OH)4 ring are involved in O…H…N hydrogen bridges to two terminal diaminopropanes and a bridging diaminopropane thus forming an O…H…N(H)2-CH2CH2CH2N(H)2 …H…O loop, in the 1:2 adduct two such O…H…N(H)2-CH2CH2CH2N(H)2…H…O loops are present. When [Ph2SiO]8[AlO(OH)]4 is allowed to react with hexamethyldisilazane, again two different products may be obtained depending on the solvent: [Ph2SiO]8[AlO2]2[AlOO-SiMe3]2[NH4· THF]2 or [Ph2SiO]8[AlOO0.5]4· 2 py. This last reaction may be viewed as an inner condensation within [Ph2SiO]8[AlO(OH)]4 loosing two equivalents of water. Both products of the reaction with hexamethyldisilazane have an inner Al2O2 four-membered cycle in common, to which Al2O4Si2 eight-membered cycles are partly fused.

New synthetic approach and structural characterization of the chloroalkylstannanes (ClCH 2) n SnCl 4− n ( n=2, 4) and the hydrolysis product [(ClCH 2) 2Sn(Cl)OSn(Cl)(CH 2Cl) 2] 2

The chloroalkylstannanes Cl 2Sn(CH 2Cl) 2 ( 1) and Sn(CH 2Cl) 4 ( 3) have been prepared in high yields by the treatment of tin tetrachloride with diazomethane under the elimination dinitrogen. The established synthetic process was modified in such a way, that the yields were considerably upgraded and the isolation of the products simplified: instead of using CH 2N 2 in solution, CH 2N 2 was transported by a nitrogen gas flow in a special apparatus. The compounds 1 and 3 were crystallized and their crystal and molecular structures were obtained (for 1 this was a redetermination) by X-ray diffraction [ 1: orthorhombic; space group: Pmmn; a=7.760(2), b=10.190(2), c=4.840(1) Å; V=382.7 Å 3; Z=2. 3: monoclinic; space group: C2/ c; a=9.849(2), b=9.872(2), c=10.611(2) Å, β=96.30(3)°; V=988.3 Å 3; Z=4]. Both molecular compounds are connected in the solid state by either intermolecular Sn⋯Cl interactions ( 1) or weak H⋯Cl bridges ( 3). In the crystal structure of 1 the molecules adopt almost perfect C 2 v symmetry (the twofold axis bisecting the ClSnCl angle) and stack together in such a way, that all chlorine atoms are oriented in one direction. The two tin bonded chlorine atoms form an SnCl 2 scissor which chelates the neighboring molecule via the two Sn⋯Cl contacts (3.76 Å) upgrading the coordination number at tin from 4 to 6. This feature can best be seen from the increase of the CSnC bond angle to 135.4° (instead of tetrahedral) and from the simultaneous decrease of ClSnCl to 98.9°. In the crystal of 3 the central tin atom is almost tetrahedrally coordinated by four carbon atoms, but there are still weak intermolecular interactions caused by H⋯Cl bridges (3.01 Å). Treatment of compound 1 with moisture converts it to the chlorostannoxane (ClCH 2) 2ClSnOSnCl(CH 2Cl) 2 ( 2) which turns out to crystallize as a distinct centrosymmetric dimer. Compound 2 crystallizes in the monoclinic space group P2 1/ n ( a=8.842(2), b=18.704(4), c=8.693(2) Å, β=109.48(3)°, V=1352.3 Å 3, Z=2) and the dimeric molecule deviates from the typical ladder like structure of chlorostannoxanes with the three adjacent four-membered cycles (SnClOSn, Sn 2O 2, SnClOSn) by further Sn⋯Cl interaction (3.450 Å). Through this interaction all tin, tin bonded chlorines and oxygen atoms become assembled within a common plane which is wrapped up by eight CH 2Cl-groups above and below this plane (overall point symmetry almost C 2 h ). The ten atoms (4Sn, 4Cl, 2O) can also be described as two oxygen centered interpenetrating Cl 2Sn 3O distorted hexagons. The tin atoms are either in trigonal bipyramidal or octahedral distorted coordination spheres, while the oxygen atoms are trigonal planarly coordinated by three tin atoms.

The 1,4,7,10,13-Pentaoxacyclohexadecane-14,16-Dione Complex with Potassium Thiocyanate: Crystal Structure

The complex of 1,4,7,10,13-pentaoxacyclohexadecane-14,16-dione (L) with potassium thiocyanate, C11H18O7· KNCS (I), is prepared and characterized by X-ray diffraction analysis: space group C2/c, a = 26.810 A, b = 7.834 A, c = 20.504 A, β = 129.19°, Z = 8. The crystal structure is solved by the direct method and refined anisotropically by the full-matrix least-squares method to R = 0.038 for all 2929 unique measured reflections (CAD4 automated diffractometer, λMoKα). Structure I is built of [KL(NCS)] monomers of the host–guest type, which are united into [K2L2(NCS)2] dimers containing four-membered KNKN cycles. In the crystal, the dimers are united into infinite polymeric double chains (along the b axis) by K···O=C outer bonds. The K+ cation (CN 8) does not lie in the plane of the L crown ligand but is located above it. The coordination polyhedron of the K+ cation is irregular; its vertices are occupied by five ether O atoms of one L ligand, two N atoms of two SCN ligands, and one carbonyl O atom of the adjacent L ligand.

Lithium tetraorganodichalcogenoimidodiphosphinates. Crystal structure of [Li{(OPPh 2)(SPMe 2)N}·2H 2O] 2, a dimer formed through oxygen-bridging phosphorus ligands

Lithium tetraorganodichalcogenoimidodiphosphinates, Li[(XPR 2)(YPR′ 2)N], were prepared and investigated by means of IR and multinuclear ( 1H, 13C, 31P) NMR spectroscopy. The crystal and molecular structure of lithium P, P-dimethyl- P′, P′-diphenyl- P-thioimidodiphosphinate was determined by X-ray diffraction. The asymmetric unit contains two independent dimeric associations, [Li{(OPPh 2)(SPMe 2)N}·2H 2O] 2, built up through O–phosphorus ligand bridges and separated by normal van der Waals distances. This results in the formation of a perfectly planar Li 2O 2 four-membered cycle with tetrahedral coordination around each metal atom completed by two additional O-water atoms. The sulfur atoms of the monothioimidodiphosphinato groups, which are not involved in coordination to a metal center, are on opposite sides of the Li 2O 2 cycle.