Cyclobutadiene Ring Research Articles

Kinetics of nucleophilic addition to co-ordinated cyclobutadiene

A kinetic study in acetone of the equilibrium addition of tris-(p-chlorophenyl)phosphine to the cyclobutadiene ring in cyclobutadienedicarbonylnitrosyliron hexafluorophosphate suggests that the mechanism of addition does not involve initial attack at the metal.

ChemInform Abstract: POLYCYCLIC SYSTEMS CONTAINING SMALL‐MEMBERED RINGS

AbstractEs werden Synthesen von Polycyclen, z.B. (I) und (II), angegeben, die einen potentiellen Cyclobutadien‐Ring enthalten.

Isolation of a tricyclo[6,2,0,02,5]deca-1,3,5,7,9-pentaene

The compound (7), containing two cyclobutadiene rings, was isolated as blue needles by heating E,E-1,2-diphenyl-3,4-bis(t-butylphenylethynylmethylene)cyclobut-1-ene (5).

Polycyclic systems containing small-membered rings

Abstract

Nucleophilic additions of phosphines to a π-cyclobutadiene ligand

Nucleophilic addition of phosphines to the cyclobutadiene ring in [( h 4-C 4H 4)Fe(CO) 2 NO] +PF 6 − leads to the formation of ( exo-phosphonium- h 3-cyclobutenyl) dicarbonylnitrosyliron hexafluorophosphate.

The crystal structure of di-μ-bromobis(μ-tetraphenyl-cyclobutadiene)tetracarbonyldimolybdenum(I)

The crystal structure of di-μ-bromobis(μ-tetraphenylcyclobutadiene)tetracarbonyldimolybdenum(I) has been determined by X-ray diffraction techniques using diffractometer data. The red crystals are triclinic with a = 11.306(4), b = 13.681(4), c = 17.561(10) Å and α 105.58(1), β 91.14(2) and γ 108.50(5)°. The space group indicated by the intensity statistics is P 1 and, with two dimer molecules per cell, no molecular symmetry is required ( D m 1.59 g/cm 3 and D c 1.585 g/cm 3). The structure was solved by the heavy atom method and refined by least-squares methods to a final R of 0.056 for 8089 observed reflections (2θ limit of 135° with copper radiation) used in the analyses. The average MoBr distance in the bromine bridged dimer is 2.637 Å, with a MoMo distance of 2.954 Å. The mean MoC (cyclobutadiene ring) is 2.253 Å and the MoC (carbonyl) is 2.008 Å. The average CC distance in the planar cyclobutadiene rings is 1.469 Å.

THE REACTION BETWEEN π-CYCLOPENTADIENYLDI-CARBONYLCOBALT AND PHENYLETHYNYLSILANE, AND AN X-RAY CRYSTALLOGRAPHIC INVESTIGATION OF ONE OF THE PRODUCTS, (π-CYCLOPENTADIENYL)-[trans-DIPHENYL-DI(TRIMETHYLSILYL)-CYCLOBUTADIENE]-COBALT

Abstract This is a report of the broad range of reactions and products that occur in refluxing xylene when π-cyclopentadienylcobalt or (π-cyclopentadienyl)-dicarbonylcobalt react with either symmetric or unsymmetrical acetylenes, specially when one of the substituents of the acetylene is an aromatic moeity. Since these reactions produce a variety of products, several of which are cis- and trans- tetrasubstituted cyclobutadiene-cobalt isomers, mnr and mass spectral methods were used to distinguish between them. In order to obtain an independent and indisputable structure assignment for the structural isomers investigated by spectral techniques, the crystal structure of the title compound was investigated by x-ray crystallographic techniques. The compound crystallizes in space group Pbca with the following cell dimensions: a = 29.622(7), b = 9.967(2) and c = 17.140(3) Å; V = 5060.46 Å3; D(exp) = 1.23(2) gm-cm−3, D(calc) = 1.24 gm-cm−3 for Z = 8 molecules/unit cell. The intensity data were collected with MoKα radiation (Λ = 0.71069 Å) using a computer-controlled diffractometer equipped with a graphite monochromator. In all 6331 reflections were collected of which 3173 were independent and had F 0 2 ± 3[sgrave] (F 0 2). The data were corrected for absorption and the transmission coefficients ranged from 0.72 to 0.79. The (π-cyclopentadienyl) ring is planar and has normal Co–C and C–C distances which average 2.049(7) and 1.389(17) Å, respectively. The Co–(Cp ring centroid) distance is 1.67 Å and the ring librates about this axis to a small degree which is not, however, large enough to affect the C–C distances. The average value of the C–C–C angle in the π-cyclopentadienyl ring is 108° indicating that it is planar and, in fact, the largest deviation of any carbon from the least-squares plane is 0.006 Å. In the Co-cyclobutadiene moiety, the Co–C and C–C distances are 1.982(15) and 1.467(3) Å and the Co–(cyclobutadiene ring centroid) distance is 1.69 Å. The angle between the normals of the five- and four-membered rings is 1.6°. The phenyl rings and trimethylsilyl fragments have normal distances and angles and the phenyl rings are planar. The two silicon and two carbon atoms of the phenyl rings linked to the π-cyclobutadiene moeity are out of the mean plane of the ring and bend away from the Co atom. Finally, and most important, the four-membered ring is planar (the largest deviation from planarity is 0.003 Å) and the four C–C distances are the same length; however, the internal angles are not 90.0°. Instead, the two angles at carbons bonded to phenyl rings have values of 88.1(2)° and 88.4(2)° while those at carbon atoms bonded by silicons have values of 91.6(2)° and 91.8(2)°. The final discrepancy indices for this structural analysis were R 1 = 0.038 and R 2(F) = 0.044.

Vibrational spectra of and bonding in (cyclobutadiene)iron tricarbonyl

The vibrational spectrum of (cyclobutadiene)iron tricarbonyl is reported and assigned. This is the first reported detailed description of the vibrations of an unsubstituted, π-complexed cyclobutadiene ring.

Absorption and emission spectra of 2, 3-benzobiphenylene—Comparison with pariser-parr-pople SCF-MO-CI calculations

2,3-Benzobiphenylene was prepared by a synthetic route starting with α,α,α′,α′-tetrabromo orthoxylene. Its electronic absorption, fluorescence, delayed emission, and fluorescence polarization spectra were experimentally characterized. A semi-empirical SCF-MO-CI method was used to calculate properties associated with the transitions. With the aid of the computation the electronic transitions of 2,3-benzobiphenylene are assigned. A table of ground and excited state bond orders was compiled. Electron densities for filled and unfilled MO's were generated and are presented schematically. By comparison of theory and experiment, 2,3-benzobiphenylene is characterized as a single aromatic system that contains an essentially aromatic four-membered cyclobutadiene ring.

Ground states of conjugated molecules—V

Abstract Resonance energies have been calculated for a number of polycyclic aromatic hydrocarbons containing a cyclobutadiene ring, using the SCF MO method developed in previous papers of this series. 2 The calculated values seem to correlate well with the properties reported for these compounds. The calculated heat of formation of biphenylene leads to a new value for the strain energy.

Kristallstruktur des Benzol‐Addukts des 1,2,3,4‐Tetramethylcyclobutadien‐nickel(II)‐chlorids, (C8H12, NiCl2)2, C6H6

AbstractCrystals of 1,2,3,4‐tetramethylcyclobutadiene‐nickel dichloride, C8H12NiCl2, are monoclinic, a = 16,01, b = 8,01, c = 16,45 Å; β = 111° 5′; Z = 8; Space group P21/n. Crystals of the benzene containing solvate, 2C8H12NiCl2, C6H6, lose benzene rapidly but are stable for several days when enclosed in glass tubes. The unit cell of the solvate is monoclinic, a = 8,311, b = 11,944, c = 12,715 Å; β = 103° 2′; space group P21/c; it contains 4 molecules of complex plus 2 molecules of benzene. The approximate structure has been derived by standard methods and refined by least‐squares analysis to an R factor of 0,069. The molecule, as it exists in the solvate, is a dimer, C8H12Ni2Cl4C8H12. Each Ni atom has on one side the four atoms of the cyclobutadiene ring (Ni‐C, 2,00 to 2,05 Å), and on the other side 3 Cl neighbours, two shared with the second Ni to form a 4‐membered ring (Ni‐Cl, 2,35 Å) and one unshared (Ni‐Cl, 2,26 Å). The cyclobutadiene ring is planar and appears to be square or very nearly so (C‐C, 1,40 to 1,45 Å). The methyl groups are displaced outwards (i.e. away from the Ni atom) by 0,12 to 0,19 Å, probably as a result of steric interference with the Cl atoms. The benzene rings lie between, and approximately parallel to, pairs of C8H12 groups belonging to different molecules, and undergo a strong rotational disorder in their own planes.

Crystal Structure of Tetraphenylcyclobutadiene Iron Tricarbonyl

THERE has been much recent interest1–5 in the possible existence of the cyclobutadiene ring system in transition metal complexes, and a crystal structure determination6 has verified that Criegee and Schroder's C8H12NiCl2 is indeed tetramethyl cyclobutadiene nickel dichloride. The present investigation similarly verifies the conjecture4,5,7 that the compound Fe(CO)3 (C6H5C2C6H5)2 of Hubel et al. 4 is tetraphenyl-cyclobutadiene iron tricarbonyl.

The electronic structure of the complex Fe 2C 10H 4O 8

The electronic structure of the complex Fe 2C 10H 4O 8, the structure of which has recently been determined by X-ray analysis, is discussed in terms of molecular-orbital theory. It is suggested that through the formation of bent three-centre π-orbitals the electronic structure is similar to that of the hypothetical symmetrical case involving a cyclobutadiene ring.