Rolf Gleiter

A CNDO/INDO molecular orbital formalism for the elements H to Br. theory

A CNDO and INDO formalism is presented that can be used for any atom combination up to bromine under inclusion of the first transition metal series. The semiempirical parameters were chosen to reproduce results ofab initio calculations on metalorganic compounds. The calculational results are invariant to rotations of the coordinate system but not to a general transformation into other basis functions. The one-center Coulomb-expressions were selected in order to include intraatomic correlation contributions. Within the CNDO model this could be achieved by the scaled monopole termF0, while in the INDO framework the one-center Coulomb integrals are given as a sum of the monopole-contributionF0 and higher multipole contributions expressed as a linear combination of Slater-Condon parameters. The invariance problem in the case of local rotations within the INDO approximation was solved by considering the combination of one-center Coulomb and exchange integrals as a function ofl but independent ofm. The two-center electron-electron interaction terms were calculated via the Dewar-Sabelli, Ohno-Klopman relation. Penetration effects were treated according to Fischer and Kollmar. For the resonance integralHμvAB parameters are used which carry information related to the directed nature of the chemical bond by using optimized Klondyke functions. The core-core repulsion is constructed as a superposition of a soft potential function, describing polarization effects of the atomic cores, and a hard repulsion function, avoiding the collapse of the atomic cores with decreasing distance.

Hydrogenation of buckminsterfullerene C60 via hydrozirconation : a new way to organofullerenes

Hydrogenation of buckminsterfullerene C60 has been achieved via reaction with (η5-C5H5)2Zr(H)Cl (hydrozirconation). Hydrolysis of the intermediate C60 zirconium(IV) complex, [(η5-C5H5)2ZrCl]nC60Hn with n=1,2,3, yielded a mixture of C60H2n and unreacted C60, from which C60H2 has been isolated through preparative high performance liquid chromatography (HPLC).

The stabilization of centers with six valence electrons through electron-high three-center bonding

Abstract A possible method to stabilize a singlet state of a nitrene (or any other 6-valence electron center) is to approach it in a symmetrical manner with two lone pairs. The resultant electron-rich 3-center bond is generally unstable with respect to a 2-center bond. The 3-center geometry may however be stabilized when the atoms involved carry low lying d orbitals. The electronic structure of thiothiophthenes is investigated in context and a general analysis of the feasibility of electron-rich 3-center bonding in the first and second rows of the periodic table is presented.

Alkynes Between Main Group Elements: From Dumbbells via Rods to Squares and Tubes

Since its first reported synthesis from calcium carbide in 1862 by Friedrich Wöhler,1 acetylene and its alkylor aryl derivatives have developed as key reagents in organic chemistry. The CtC triple bond proved to be reactive toward electrophiles, nucleophiles, hydrogenation reagents, various catalysts, light, and heat. This high reactivity makes the CtC triple bond an ideal reagent for the formation of new C-C bonds. It is therefore of high interest in industry and research laboratories. In the latter places very often main group elements play a pivotal role as reaction partner of the CtC triple bond. In Scheme 1, we list four examples for this role. In most protocols for alkylation of acetylene or monosubstituted triple bonds such as 1 alkali or alkali earth metal salts of an acetylide anion, usually generated in situ, are used as starting materials2 (eq 1 in Scheme 1). Alkynyl 9-BBN derivatives (e.g., 4) are utilized to prepare enynones by reacting them with alkyl ethers of -ketoaldehydes3 (eq 2 in Scheme 1). Trialkylor triarylsilyl groups are frequently used to protect one end of a triple bond when the other will be functionalized. These bulky groups play also an important role to synthesize and stabilize (oligo)alkynes. To couple two different alkyne units together to a diyne, it is effective to use a cross-coupling protocol suggested by Cadiot and Chodkiewicz with a monobrominated alkyne 8 as one component4 (eq 3 in Scheme 1). Most recently, a nitrogensubstituted alkyne 10 was used to construct an aldol product 12 with a quaternary all-carbon stereocenter in a sequential one-pot procedure5 (eq 4 in Scheme 1).

Synthesis of [6.8]3Cyclacene: Conjugated Belt and Model for an Unusual Type of Carbon Nanotube

[6.8]3Cyclacene as the first hydrocarbon being a fully conjugated molecular belt has been synthesized in an eight-step reaction sequence starting from 4,6-dimethylisophthalaldehyde. It is the smallest and most strained member of the [6.8]cyclacene family, and the synthetic path offers a general route to its higher members. The structural pattern of [6.8]3cyclacene represents a model for a novel type of carbon nanotubes.

Photoelectron spectra of planar sulfur heterocycles

Abstract The photoelectron spectra of benzo[b]thiophene (2), benzo[c]thiophene (3), thieno[3,2-b] thiophene (4) and thieno[2,3-b]thiophene (5) together with 2,1,3-benzothiadiazol (6) and benzofurazan (7) have been recorded and the first three bands have been assigned to π-orbitals on the basis of band shapes and semiempirical calculations. The good agreement obtained between measured and calculated ionization potentials suggests that sulfur 3d orbital participation must be very small.

Raman scattering study of C120, a C60 dimer

Abstract A modified preparation method and results of a Raman scattering study for C 120 , a dimer of C 60 , are reported. The Raman features of C 120 are compared with those of the dimer-like oxides C 120 O and C 120 O 2 , phototransformed C 60 and with calculations.

A CNDO/INDO molecular orbital formalism for the elements H to Br. applications

The CNDO/INDO molecular orbital formalism introduced in the preceding paper has been applied to a large number of atom combinations up to bromine under the inclusion of the first transition metal series. The results are compared with experimental data (geometries, ionization potentials, dipole moments) or with the results of sophisticatedab initio calculations (one electron energies, net charges, atomic populations). The semiempirical model reproduces for a wide range of molecules the experimental andab initio data with remarkable success.

Through bond interactions of non-bonding orbitals: The n,π* states of azanaphthalenes

Abstract The electronic transitions of eleven azanaphthalenes as dilute solid solutions in monocrystalline hosts have been studied. Provisional assignments imply significant energy gaps between n,π* states and lead to a low energy forbidden π*←n excitation in 1,5- and 1,8-diazanaphthalene. These assignments are consistent only with a significant through-bond coupling of the non-bonding orbitals, an analysis of which is presented.

Structure and reactivity of norbornene and syn-sesquinorbornene

Abstract The origin of the observed non-planarity of the syn-sesquinorbornene (syn-tetracyclo-[6.2.1.1 3,6 .0 2,7 ]dodec-2(7)-ene) π system is discussed in terms of simple molecular orbital theory. Calculated out-of-plane bending energies for the double bonds in cyclohexene, bicyclo[2.2.2]oct-2-ene, bicyclo[2.1.1]hex-2-ene, bicyclo[3.2.1]oct-6-ene, and bicyclo(2.2.1]hept-2-ene closely parallel the published cycloaddition rate constants for these compounds, indicating that ease of deformation may be a rate determining factor. The “staggering effect” considered by Houk et al . is discussed and it is demonstrated that this effect is not equivalent with the norbornene “x” factor introduced by Huisgen et al .