I. P. Gloriozov

Transition metal complexes with heterocyclic analogs of fluorene 1. Synthesis, structures, and haptotropic rearrangements of tricarbonylchromium complexes of dibenzothiophene

The complex formation of dibenzothiophene with chromium carbonyl complexes of the general formula L3Cr(CO)3 (L = Py, NH3, or CO) afforded η6-C12H8SCr(CO)3 (1). In the presence of tetramethylethylenediamine, complex 1 was selectively metallated with BuLi at position 4 of the coordinated ring to form η6-4-LiC12H8SCr(CO)3 (2). In decane, the tricarbonylchromium group is reversibly and intramolecularly migrates from the unsubstituted to substituted ring due to the inter-ring haptotropic rearrangement (IRHR) at 130 °C for 100 h. In decane, the rate constant of IRHR was estimated experimentally by 1H NMR spectroscopy and theoretically by the density functional theory (DFT).

A density functional study of the structure and potential energy surface of dibenzenechromium and its alkylated derivatives

Density functional calculations were performed with the nonempirically constructed PBE functional and TZ2p basis set to study the potential energy surfaces of several dibenzenechromium derivatives containing methy1 and tert-buty1 groups in aromatic ligands. The method was shown to correctly describe the structure and intramolecular dynamics of bis-arenechromium complexes. It allows barriers to rotation about the metal-ligand bond to be calculated and detailed information to be obtained about the shape of the potential curves that correspond to this rotation. The potential energy surfaces of polymethylated dibenzenechromium derivatives contained several minima close in energy; these minima largely corresponded to eclipsed conformers. The potential curves for rotation about the metal-ligand bond in dibenzenechromium and its methylated derivatives reveal the presence of staggered conformers as transition states. Irrespective of the number of methyl groups present in both ligands, we observed no substantial changes in barrier heights, which were about 1 kcal/mol. Conversely, the introduction of bulky tert-butyl groups destabilized eclipsed conformations. Ensuing steric strain caused substantial out-of-ring-plane displacements of the Cipso-t-Bu bonds away from the chromium atom, distorted aromatic ring planarity, and substantially increased barriers to rotation, to 8–10 kcal/mol.

Intramolecular noncovalent interactions: Bis(toluene)chromium(0) conformers

The structure of trans- and cis-conformers of bis(toluene)chromium(0) and the intramolecular interactions in them are studied by means of MP2 and density functional theory along with topological and NBO analyses. It was concluded for the first time that the locations of two hydrogen atoms of each methyl group between the phenyl ring planes in the most stable cis-conformer of bis(toluene)chromium(0) are largely determined by the stabilizing interactions of methyl C-H bonds and their hydrogen atoms with the metal atom and chromium-carbon bonds. It was concluded from the obtained data that the C-H...Cr contacts in the studied conformers should be considered as hydrogen bonds rather than agostic interactions. Contrary to the existing conception of the quantum theory of atoms in molecules, repulsive interaction is shown to occur between the pairs of hydrogen atoms of the two methyl groups in bis(toluene)chromium(0) cis-conformers rather than the stabilizing hydrogen-hydrogen interactions.

Quantum chemical study of butane isomerization on clusters of aluminum and cobalt chlorides. Mixed complexes

Activated complexes and routes of the model catalytic process, viz., butane isomerization by the aluminum and cobalt chloride complexes, were calculated by the DFT/PBE/TZ2p quantum chemical method. Alkanes are activated via the alkyl mechanism to form binuclear bimetallic alkyl clusters, where the Co atoms are linked by the metal-metal bonds. The revealed binuclear complexes can transform into bimetallic alkyl clusters with similar energy in which the transition metal atoms are linked by bridges of the Cl atoms. The full model of the catalytic cycle was developed for the maximum multiplicity (7), and particular key regions related to the cleavage and formation of the C-C bonds were calculated with a lowered multiplicity (5 and 3). The sequence of mutual rearrangements of the polynuclear complexes provides the possibility of C-C bond cleavage in alkanes and formation of the metal-carbon bonds. The calculated energy barriers of particular stages of the cyclic catalytic process of butane isomerization are not higher than 29 kcal mol−1 for multiplicity 7 and by ∼10 kcal mol−1 lower for a lower multiplicity.

The mechanism of allyl isomerization of unsaturated compounds catalyzed by organomagnesium clusters

The paper presents a density functional theory investigation of the mechanism of allyl isomerization of olefins on magnesium clusters for the example of the Mg4-allylbenzene system. The rearrangement of the cluster compound corresponding to the insertion of the tetranuclear cluster at a C-H allylbenzene bond into a structure derivative from 2-methylstyrene is an activationless reaction. The limiting step is the liberation of the cluster nucleus capable of interacting with another allylbenzene molecule. Cluster decomposition competes with this process; this conclusion is in agreement with experimental short lifetimes of cluster magnesium hydride catalysts.

Quantum chemical study of butane metathesis on mixed aluminum and cobalt chloride complexes

Activated complexes and routes of the model catalytic butane metathesis in the presence of mixed complexes of aluminum and cobalt chlorides were calculated by the quantum chemical DFT/PBE/TZ2p method. The earlier predicted bimetallic alkyl clusters containing Co-Co dimeric bonds are key intermediates leading to the formation of both isomerization products and products of alkane metathesis (pentane and propane molecules in the case of butane). The sequence of mutual rearrangements of the polynuclear complexes provides a possibility of cleavage and formation of C-C bonds in alkanes and metal-carbon bond formation. The full model of the catalytic cycle was constructed for the maximum multiplicity (7) of the catalytic system, and individual key regions related to C-C bond cleavage and formation were calculated with a lowered multiplicity (5 and 3). The obtained energy barriers of individual stages of the cyclic catalytic process of butane metathesis are not higher than 33 kcal mol−1 for multiplicity 7 and are lower by ∼15 kcal mol−1 for a lower multiplicity.

The inclusion of anion-cation interactions in calculations of the structure of dibenzenechromium salts by density functional theory

The structures of di(η6-benzene)chromium, its isolated radical cation, and model fragments of crystals (C6H6)2 Cr+·X-(X = I, Br) were calculated using density functional theory with the PBE functional and an extended split basis set with a relativistic effective core potential. Ignoring (C6H6)2Cr+· interactions with the counterion was shown to cause some exaggeration of the Cr-C distances in the isolated di(η6-benzene)chromium cation compared with the corresponding X-ray structure data.

Molecular structure of 6-(N,N-dimethylamino)fulvene from a joint gas-phase electron diffraction and quantum-chemical study

The molecular structure of 6-(N,N-dimethylamino)fulvene was studied by gas-phase electron diffraction and quantum-chemical methods (HF/6-31G(d), MP2/3Z, MP2/4Z, density functional theory with the B3LYP/6-31G(d) and PBE/3Z functionals). Pronounced flattening of the nitrogen atom and equalization of the intracyclic C—C bonds were found to be a consequence of the electron delocalization in the molecule.