T. N. Gribanova

Stabilization of nonclassical types of valence bond orientation at the carbon atom in organoboron compounds

The complete topological structure of the potential energy surface (PES) of methane in the inversion region was studied by theab initio CCD(full)/6-311++G** method. The necessity of taking into account nuclear motions was shown. Penta- and hexacoordination of carbon atoms in boron-containing organic compounds was investigated by theab initio MP2(full)/6-31G** and MP2(full)/6-311++G** methods. The CB4H4Li2, CB6N2H2, and CB6O2 systems containing hexacoordinated carbon atoms correspond to rather deep minima on the relevant PES and can be the subject of synthetic studies. According to theab initio calculations, pyramidal boron-containing systems with hypercoordinated carbon atoms, which fulfill the “8e rule,” also correspond to rather deep PES minima and can be detected experimentally.

Structure and stability of the heteroannulated (8-10)circulenes: A quantum-chemical study*

The structure and stability of a new family of heterocyclic [n]circulenes CnNnYn (n = 8–10; Y = N, P, As, BF2, AlF2, GaF2) have been computationally studied using density functional theory (DFT) B3LYP/6-311G* calculations. The geometry of the compounds is determined by the balance of steric factors and effects of aromatic π-electron delocalization depending on the electronegativity of heteroatoms. An increase in the bulkiness of peripheral atoms Y and enlargement of the inner Cn cycle leads to the gradual transformation of the bowl-shaped circulene structure (Y = N, BF2) to planar and then saddle-shaped forms (Y = P, As, AlF2, GaF2). The calculations performed manifest stabilization of the heteroannulated circulenes ensured by the strong aromatic character of the conjugated five-membered rings fringing the central non-aromatic or antiaromatic [8–10] annulene rings.

Photochromic Cation Sensors

ABSTRACT Novel photochromic chemosensors for alkali-, alkali-earth and d-metal cations were synthesized and their photochemical and complexing properties investigated with the use of UV/vis, IR, 1H/7Li NMR spectroscopy and quantum chemical calculations – DFT(B3LYP/6-31G).

Sandwich Compounds of Transition Metals with Cyclopolyenes and Isolobal Boron Analogues

A series of sandwich compounds of transition metals (M=Ni, Fe, Cr) with cyclic hydrocarbon (M(CH)(n)) and borane (M(BH(2))(n)), ligands (including mixed hydrocarbon/borane sandwiches) has been studied using density functional theory (B3LYP/6-311+G(df,p)). Multicenter bonding between the central metal atom and basal cycloborane rings provides stabilization to planar cycloborane species. Large negative NICS values allude to aromatic character in the cycloboranes similar to the analogous cyclic hydrocarbons. The ability of cycloborane sandwiches to stabilize attached carbocations, radicals and carbanions is also assessed.

Quantum-chemical study of heteroanalogues of [8]circulenes and their derivatives

105 Aromaticity is one of the basic concepts of organic chemistry [1]. There are many approaches to both classification of the structure types of aromaticity and its quantification. In the simplest variant, aromaticity is associated with a six-membered ring of sp 2 -hybridized carbon atoms. At the same time, [6]radialenes 1O belonging to hydrocarbons of this type do not exhibit aromatic properties, have a chair conformation [2, 3], and tend to rapidly polymerize at room temperature.

Structure and stability of closo-hexaboranes and their heteroanalogs

The molecular and electronic structures of closo-hexaboranes B6H62–, B6H7–, and B6H8 and closo-heterohexaboranes XYB4H4 (X = Y = CH, N; X = BH, Y = CH–, N–, NH, O) were studed by the ab initio (MP2(full)/6-311+G**) and density functional (B3LYP/6-311+G**) methods. The bridging H atoms in closo-hexaboranes B6H7– and B6H8 can undergo facile low-barrier migrations around the boron cage (the barrier heights are about 10—15 kcal mol–1). All heteroboranes having octahedron-like structures with hypercoordinated N and O atoms are rather stable and can be the subject of synthetic research efforts.

Theoretical design of planar systems with hypercoordinate p elements of the second period in a nonmetallic environment

Theoretical approaches to stabilization and design of nonclassical compounds containing p elements of the second period (B, C, N, O, F) in a nonmetallic environment are considered. Structural diversity of such systems is demonstrated, and influence of steric and electronic factors on their stability is considered.

Induced Aromaticity and Electron-Count Rules for Bipyramidal and Sandwich Complexes of s- and d-Metals

Structures and stability of an extended series of bipyramidal, sandwich and sandwich-bipyramidal mixed complexes formed by conjugated cyclic hydrocarbons (CH)n with s(Li, Na, K, Be, Mg, Ca) and d(Cr, Mn, Fe) metals have been studied using DFT B3LYP/6-311+G(df,p) calculations. Stable structures of the compounds satisfy a general (6n + 6d + 12c) electron-count rule, where n stands for total number of the basal hydrocarbon rings, d is total number of d-metal centers (or separate sandwich moieties) and is total number of apical metal-carbonyl groups. It is shown that stabilization of the studied polyhedral organometallic structures (induced aromaticity) is caused by filling 6 -electronic shells of basal (4-6)-membered cycles provided by donation of additional electrons from metal centers thereby acquiring closed 18-

Extended organoboron structures containing several planar tetracoordinate carbon atoms

101 Due to extensive studies of molecular electronic devices, the search for new one-dimensional organic and organometallic compounds with semiconducting, conducting, or superconducting properties is becoming ever more important [1]. The focus of this search is currently on different conjugated organic, organometallic, and inorganic polymeric systems [1–3]. Recently, nonclassical systems 1 – 3 with planar tetracoordinate carbon centers have been suggested for use as novel building blocks for polymers [4–6]:

Quantum-chemical investigation of structure and stability of [n]-prismanes and [n]-asteranes

The study by DFT [B3LYP/6-311G(2df,p)] method of structural and energy characteristics peculiar to [n]-prismanes and [n]-asteranes demonstrated that prismanes of n = 3–10 and asteranes of n = 3–7 possessed a stable structure of Dnh-symmetry; the Dnh-geometry was distorted in the subsequent terms of the series.