Central Four-membered Ring Research Articles

2,4-Bis(4-methoxyphenyl)-3-phenyl-1,3,2,4-thiazadiphosphetidine 2,4-disulfide

The structure of the title compound, C20H19NO2P2S3, features isolated units. Each molecule consists of a central four-membered ring. The terminal S atoms are in a trans configuration above and below the plane defined by the central ring, whilst the phenyl substituent is in almost perpendicular relative to the central ring.

Synthesis and structure of novel [Ph(RO)PSe2]– complexes

Reaction of (PhPSe2)2(Woollins reagent) with NaOR (R = Me, Et, (i)Pr) gives the non-symmetric phosphonodiselenoato anions [Ph(RO)PSe2]- which can be complexed to a range of metals. The nickel complex Ni[Ph(MeO)PSe2]2 adopts a square-planar ML2 structure while the cadmium complex Cd[Ph(MeO)PSe2]2 displays a dimeric M2L4 structure. Two different lead complexes are observed, one consisting of PbL2 units joined by Pb...Se interactions to form distinct dimeric pairs. The other displays a novel dimeric structure built around a central four-membered Pb2Se2 ring. All new compounds have been characterised spectroscopically (31P, 1H, 13C NMR, IR, mass spectroscopy), by elemental analysis and five demonstrative X-ray structures are reported.

Cyclobutadiene Dianions Consisting of Heavier Group 14 Elements: Synthesis and Characterization

The first "heavy" cyclobutadiene dianions (CBD2-), tetrakis(di-tert-butylmethylsilyl)-1,2-disila-3,4-digermacyclobutadiene dianion 22- and tetrakis(di-tert-butylmethylsilyl)tetrasilacyclobutadiene dianion 42-, have been synthesized by the reductive dehalogenation of the corresponding precursors with potassium graphite in THF. Structural characterization of [K+(thf)2]2.22- and [K+(thf)2]2.42- has been achieved by X-ray crystallography, showing that the central four-membered ring is significantly folded and has two eta2-1,3-coordinated potassium cations accommodated above and below the ring. The "heavy" CBD2-'s 22- and 42- were found to be nonaromatic compounds, a conclusion that was supported by nucleus-independent chemical shift (NICS) calculations showing a lack of diatropic ring current effects.

The crystal structures of the chiral alkyllithium bases [n-BuLi.(-)-sparteine]2 and [Et2O.(i-PrLi)2.(-)-sparteine

The crystal structures of the two chiral alkyllithium bases [n-BuLi.(-)-sparteine]2 (1) and [Et2O.(i-PrLi)2.(-)-sparteine] (2) have been determined. For compound 1, a symmetric dimer is observed in the solid state, with two (-)-sparteine ligands coordinating to the lithium centers. Because of steric reasons, compound 2 crystallizes as an unsymmetric dimer with the four methyl groups pointing away from the sterically demanding (-)-sparteine ligand. Compound 2 contains one four-coordinate lithium center [coordinated to (-)-sparteine] and one three-coordinate lithium center (coordinated to Et2O). As a result of this arrangement, significantly different Li-C distances are found in the central four-membered ring of compound 2.

Crystal structure of a binuclear polymeric self-assembled lead(II) complex.

A polymeric self-assembled complex [[Pb(pydc)(pydc-H2)(H2O)2]2]n is prepared from the complexation of a novel pyridine containing self-assembling system, LH2, [pyda-H2]2+[pydc]2- (pyda = 2,6-pyridindiamine and pydc-H2 = 2,6-pyridinedicarboxilic acid) and lead(II) nitrate in 84% yield. The characterization was performed using X-ray crystallography. The crystal system is triclinic with space group P1 and two molecules per unit cell. The unit cell dimensions are a = 6.913(2) A, b = 10.687(4) A and c = 11.182(4) A with alpha = 92.805(6) degrees, beta = 101.821(6) degrees and gamma = 95.688(6) degrees. The final R value is 0.0373 for 4633 reflections measured. This compound is a nine-coordinate binuclear complex with two metal fragments linked via the central four-membered Pb2O2 ring. The crystal also contains a neutral [pydc-H2] molecule, that form hydrogen and coordination bonds that dominate the crystal packing, by forming layers of molecules.

Bis(μ-quinolineN-oxide-κ2O:O)bis[dichlorocopper(II)], a powder diffraction study

The crystal structure of the title compound, [Cu2Cl4(C9H7NO)2], has been determined from powder diffraction data. The crystals are built of dinuclear complex mol­ecules, with a central four-membered Cu2O2 ring located about a crystallographic inversion centre, which involves two Cu atoms, each carrying two terminal chloro ligands each [Cu—Cl = 2.213 (8) and 2.222 (8) A] and two O atoms of the quinoline N-oxide ligand. The Cu atom has a square-planar coordination, with considerable distortions due to the four-membered ring [O—Cu—O = 78 (1)° and Cl—Cu—Cl = 100.2 (3)°].

A seven-coordinate pyridine-2,6-dicarboxylate-bridged cadmium(II) complex, at 110 K

The reaction of cadmium(II) chloride monohydrate with a self-assembling pyridine-containing ligand, LH2 {LH2 is [H2pyda]2+[pydc]2−, where pyda = 2,6-di­amino­pyridine and H2pydc = pyridine-2,6-di­carboxyl­ic acid}, in water leads to the formation of a centrosymmetric dinuclear CdII complex, di-μ-pyridine-2,6-di­carboxyl­ato-bis­[tri­aqua­cadmium(II)], [Cd(pydc)(H2O)3]2·2H2pydc or [Cd2(C7H3NO4)2(H2O)6]·2C7H5NO4. Each Cd atom is seven-coordinate and has a distorted pentagonal-bipyramidal geometry. The two metal fragments are linked via the central four-membered Cd2O2 ring and there is no [Hpyda]+ moiety in the structure of the complex. The structure self-assembles into layers via hydrogen bonds.

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 (72−) are also studied by 13C NMR measurements. The charge distribution found closely resembles the predictions of the simple HMO model and reveals that 72− 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.

2,4-Bis{[6-(2,2-dimethylpropyl)-3-ethyl-1,3-benzothiazol-2(3H)-ylidene]methyl}cyclobutenediylium-1,3-diolate

The title compound, C34H40N2O2S2, adopts a trans conformation. The four conjugated Csp2-Csp2 single and double bonds of the polymethinic moiety, which bridges both heterocyclic end groups and the central four-membered ring, display nearly equal bond lengths. The molecule is nearly planar, with interplanar angles between the benzothiazole end groups and the central four-membered ring of 6.9 (1) and 7.7 (1) degrees; the angle between the heterocyclic systems is 1.8 (1) degrees. The crystal packing involves pi-stacking effects, with intermolecular C...C distances varying from 3.755 (3) to 3.991 (3) A.

Di-μ-methoxo-bis({N,N′-bis[2-(3,5-dimethylpyrazol-1-yl)ethyl]amine-κ3N}copper(II)) bis(hexafluorophosphate)

The title compound, [Cu2(C14H23N5)2(CH3O)2](PF6)2, has a doubly methoxo-bridged centrosymmetric copper dimer cation involving two tridentate bis­(pyrazolyl)­amine ligands. The geometry of each CuII atom is a distorted square pyramid with two N atoms of the pyrazole in bis­[2-(3,5-di­methyl-1-pyrazolyl)­ethyl]­amine (bpea) and two μ2-bridging O atoms of the methoxo ligands forming the basal plane, and the amine N atom occupying the axial position. In the bridging plane, the Cu—O bond lengths are 1.940 (4) and 1.942 (4) A, and the bond angles for O—Cu—O and Cu—O—Cu are 76.1 (2) and 103.9 (2)°, respectively. The Cu⋯Cu distance is 3.058 (1) A. The central four-membered ring lies on an inversion centre.

Violene/Cyanine Hybrids as Electrochromic Systems. Part 3: Heterocyclic Onium End Groups

Synthesis, cyclic voltammetry (CV) and spectroelectrochemistry (SE) of tetra-onium salts 3OX+4·4BF4−and 6OX+4·4PF6− are presented for both systems. Cyclic voltammograms display several reduction and oxidation peaks containing at least one reversible pair. The colorless tetracations on reduction reversibly develop long wavelength absorptions. Absorption bands arise which are attributed to 3RED+2 and 6RED/OX+2, respectively. The latter is further reversibly reduced to colorless 6RED0 for which a cyclic structure with a central four-membered ring is proposed. Radical ions like 3 (6)SEM+3 and 3 (6)SEM+1 were not detected by CV or SE. PM3 calculations of 6OX+4 down to 6RED0 change and verify two perpendicular cyanine units in 6RED/OX+2 as well as the cyclic structure for 6RED0 which is of 29.86kcal/mol more stable than the corresponding acyclic one. Systems 7–12 described in the literature are discussed as vinylogous examples of A which also display reversible two electron transfer with strong changes in color.

Isomerism of dimeric cis-ethene-1,2-di(alkylamido)gallium hydrides and chlorides

Dichlorogallane [HGaCl2]21 can be prepared in quantitative yield from equimolar quantities of GaCl3 and Et3SiH at −13 °C in the absence of a solvent. Treatment of 1 with dilithium N,N′-di-tert-butyl-cis-ethenediamide at −78 °C leads to high yields of [(tBu2N2(CH)2)GaH]22. According to IR and NMR observations, compound 2 exists in the form of two isomers in benzene solution. Crystallization from pentane affords only one isomer which was identified as a centrosymmetrical dimer with a four-membered ring (Ga–N)2 as the core unit, two hydrogen atoms in trans position and two five-membered rings fused to opposite edges also in trans position (type B). The analogous reaction of [tBu2N2(CH)2]Li2 with anhydrous [GaCl3]2 gives the corresponding chloride 3 which exists as only one isomer in solution. Crystals obtained from hexane contain four independent dimeric molecules, all of which have the same structure with inequivalent gallium atoms owing to a redistribution of the chloride ligands. The central four-membered ring (Ga–N)2 has the two five-membered rings fused to neighbouring edges in trans position, and the two chlorine atoms are associated with the same gallium atom. This isomer [tBu2N2(CH)2]Ga(GaCl2) 3 (type D) is unprecedented in the structural chemistry of the “diazabutadiene” complexes of Group 13 elements. The analogous cyclohexyl compound was prepared in high yield following the same route. It is formed as only one isomer which has the centrosymmetrical structure of type B, [(cHex2N2(CH)2)2GaCl]2 (cHex = cyclohexyl). The isomerism is probably governed by steric effects.

SYNTHESIS AND CHARACTERIZATION OF COMPLEXES OF Me3M (M = Al, Ga) OR Et3In WITHBIS(DIMETHYLAMINO)-2-PROPANOL. X-RAY CRYSTAL STRUCTORE OF THE [Me2GaOCH(CH2NMe2)2]2 DIMER

Reaction of R3M with bis(dimethylamino)-2-propanol gave the dimeric compounds [R2MOCH(CH2NMe2)2]2 (R = Me, M = AI, 1; R = Me, M = Ga, 2; R = Et, M = In, 3). The resulting compounds have been characterized by elemental analyses, 1H NMR and mass spectroscopy. The crystal structure of 2 has been determined by X-ray analysis. 2 contains a five-coordinate gallium center with a central four-membered Ga2O2 ring and a Ga-N dative bond. The geometry around the Ga atom can be described as a distorted trigonal bipyramid with a rather long Ga-N bond.

The Hydrated Tosylate of Dimeric 2'-Hydroxy-4-N-methylstilbazolium

The centrosymmetric dimeric cation in the title compound, bis(2′-hydroxy-4-N-methylstilbazolium) ditoluenesulfonate dihydrate, (C28H28N2O2)2+.(C7H7SO3)2−.2H2O is propeller-like: the planar central four-membered ring makes dihedral angles of 85.0 (2) and 63.1 (2)° with the mean planes of the pyridinium and phenyl rings, respectively. Cations, anions and water molecules are connected by hydrogen bonding.

A theoretical study on the molecular structure of biphenylene in its first excited singlet and triplet states: quantum chemical calculations on the structural changes of an antiaromatic molecule upon excitation

The structural changes accompanying the electronic excitation of the antiaromatic biphenylene molecule were studied by semiempirical quantum chemical calculations, using the AM1 hamiltonian with configuration interaction (S 1, S 2, T 1, T 2, X̃ + states). The largest bond length differences of the molecular states investigated were observed within the central four-membered ring. Potential curves of the CC bonds which connect the two benzene rings have been calculated for all molecular states investigated. For the S 0 and S 1 states, potential hypersurfaces, using the two different bond lengths of the central four-membered “cyclobutadiene” subsystem as variables, were presented. Furthermore, the geometry of 1,3-cyclobutadiene in different states (S 0, S 1, T 1, X̃ + states) was investigated with the AM1-CI hamiltonian and compared with recent 6-31G ∗ MC-SCF ab initio results.

DBU ‐ nicht einfach nur eine starke Base: Eine Eintopfreaktion für ein polycyclisches Ringgerüst mit Diphosphet ‐ Grundstruktur unter Einbeziehung von doppelt deprotoniertem DBU

DBU - Not Simply a Strong Base: A One-Pot Synthesis of a Polycyclic Framework Consisting of a Diphosphete Central Unit and Two Units of Doubly Deprotonated DBU Two condensed five-, six- and seven-membered rings are fused in a spirocyclic fashion with a central four-membered diphosphete ring in 4, which unexpectedly is formed in a simple two-component-one-pot reaction from Cl2P-CH(SiMe3)2 and DBU. The latter is doubly deprotonated and acts as a bridge via C-6 and N-8 to a P-P unit. The polyheterocycle 4 crystallizes in two modifications, whose molecular structures are almost identical.

Diphenylantimony(V) oxide halides and thiocyanate; the crystal structures of dimeric diphenylantimony(V) bromide oxide and tetrameric diphenylantimony(V) oxide fluoride and thiocyanate

Dimers containing a four-membered Sb2O2 ring with antimony atoms in distorted trigonal-bipyramidal co-ordination were obtained when either diphenylantimony(III) chloride or bromide was oxidised with tert-butyl hydroperoxide; the crystal structure of [SbPh2O(Br)]2 has been determined. Related reactions with the corresponding fluoride and thiocyanate gave products with the same stoichiometry but X-ray crystallography showed these are centrosymmetric tetramers, X2Ph2SbO(Ph2SbO2SbPh2)OSbPh2X2, which also contain a central four-membered ring. A possible mechanism for formation of these tetramers is presented. Oxidation of phenylantimony dichloride and dibromide on the other hand gave only rearrangement and decomposition products.

Trans-3-Amino-1-methyl-4-phenyl-2-azetidinone, C10H12N2O

The central four-membered azetidinone ring of the title compound is puckered significantly with an average ring torsion angle of 5.1 (1) °. Molecules form infinite twodimensional hydrogen-bonded networks via N--H.-.N [N...N 3.379 (3) A] and N--H...O [N...O 3.056 (3) A] interactions.

Azaaluminatranes Exhibiting Unusual Coordination Geometries for Aluminum

The new monomeric azaaluminatrane Al(tert-BuMe(2)SiNCH(2)CH(2))(3)N, 6, was prepared by the reaction of [Al(NMe(2))(3)](2), 7, and (tert-BuMe(2)SiNHCH(2)CH(2))(3)N, 11, and was characterized by H-1, C-13, Al-27, and Si-29 NMR, and IR spectroscopies and mass spectrometry. Its analogue Al(Me(3)SiNCH(2)CH(2))3N, 3, was structurally characterized and shown to contain a trigonal monopyramidal aluminum center. The dimeric azaaluminatrane [Al(Me(3)SiNCH(2)CH(2))(2)(HNCH2CH2)N](2), 5, possesses an unusual cis configuration of the central four-membered ring, and the aluminum atoms display a distorted trigonal bipyramidal coordination sphere. Crystal data: 3, a = 13.503(5) Angstrom, b = 10.621(4) Angstrom, c = 17.840(6) Angstrom, beta = 93.29(3)degrees, V = 2554(2) Angstrom(3), Z = 4, space group P2(1)/c, R = 5.2%; 5, a = 12.134(3) Angstrom, b = 17.049(4) Angstrom, c = 18.297(5) Angstrom, beta = 100.02(2)degrees, V = 3726(2) Angstrom 3, Z = 4, space group P2(1)/n, R = 4.6%. Al-27 NMR chemical shifts for a series of Al-N compounds with aluminum coordination numbers ranging from three to six show increased shielding with increasing coordination number.

Sulfurization and Selenization of the Halfsandwich Nitrosylmetal Complexes Cp*M(CO)2NO (M = Cr, Mo) and Cp*M(NO)I2 (M = Mo, W)

The photo-induced decarbonylation of Cp*Cr(CO)2NO in acetonitrile solution in the presence of excess sulfur leads to the cyclo-pentasulfido complex Cp*Cr(NO)(S5) (1 a), while in the case of limited sulfur supply the binuclear bis(µ-disulfido) complex Cp*2Cr2(NO)2(µ-S2)2 (4a) is formed preferentially. The corresponding reaction with elemental selenium produces Cp*2Cr2(NO)2(µ-Se2)2 (4b), irrespective of the available amount of selenium. Photodecarbonylation of Cp*Mo(CO)2NO gives only the binuclear derivates Cp*2Mo2(NO)2(µ-E2) (E = S (5a), Se (5b)) which are also obtained by treating Cp*Mo(NO)I2 with H2S or H2Se, respectively. Nitrosyl loss predominates if the tungsten complex Cp*W(NO)I2 is reacted with H2S; in an argon atmosphere the products are Cp*W(S)(S2)(I) (7a) and Cp*2W2(S)2(µ-S)2 (8a), while in air some Cp*W(NO)(S5) (3a) and the oxo compounds Cp*W(O)(S2)I (7c), Cp*2W2(O)2(µ-S)2 (8c) and Cp*2W2(S)(O)(µ-S)2 (8d) are formed. The analogous reaction with H2Se leads to Cp*W(NO)(Se5) (3b), Cp*2W2(O)2(µ-Se)2 (9c) and Cp*2W2(Se)(O)(µ-Se)2 (9d), respectively. The binuclear tungsten complexes 8a,c,d and 9c,d contain a central W(µ-E)2W framework (E = S or Se) which is unaffected by air, while terminal sulfido and selenido ligands are quantitatively converted into the corresponding terminal oxo ligands in the presence of air in CH2C12 or THF solution. With the preparation of Cp*2W2(O)2(µ-E)2 (E = S (8c) and Se (9c)), the series of dioxo complexes containing a pair of monochalcogen bridges (E = O, S, Se, Te) has become complete. The new complexes have been characterized by their IR (v(NO)), 1H and 13C NMR (Cp*) spectra as well as by electron-impact mass spectrometry. According to the X-ray structure analyses, the binuclear compounds Cp*2Cr2(NO)2(µ-S2)2 (4a) and Cp*2Mo2(NO)2(µ-Se2)2 (5b) contain two 14-electron [Cp*M(NO)2] fragments which are connected by a pair of dichalcogen (η1,η2-E2) bridging ligands (M = Cr or Mo, E = S or Se). The central M2E2 four-membered ring is not planar, and the binuclear molecules are chiral.