Chemistry of Electronically Excited Ruthenium Polypyridine Complexes: III.1 Electronic Structure of Complexes cis-[Ru(2,2'-bpy)2(4,4'-bipy)(X)]q

The results of ab initio quantum-chemical calculations of isolated ruthenium(II) complexes cis- [Ru(bpy)₂(bipy)(X)]⁴4q (bpy is 2,2'-bipyridyl, bipy is 4,4'-bipyridyl; X = NH₃, Cl^-, Br^-, CN^-, NO^- ₂, ONO^-, MeCN, and NO⁺) are presented. Analysis of the charge distributions and the orbital structures of the complex ions points to absence of strong -acceptor bonds Ru-bpy, Ru-bipy, and Ru-X (X = NO⁺), to delocalization of -electron density under the action of strong donors X, to localized nature of lowest unoccupied molecular orbitals, and to special position of the nitrosyl complexes in this series.     

Halogenation of π-cyclopentadienyltricarbonylrhenium and π-cyclopentadienyl(triphenylphosphine)dicarbonylrhenium

Conclusions The following previously unknown rhenium semicoordinaticn compounds were synthesized: [-C₅H₅Re(CO)₂PPh₃Cl]⁺Cl^–, [-C₅H₅Re(CO)₃Cl]⁺Cl^–, [-C₅-H₅Re(CO)₂PPh₃Cl]⁺Be₄, [-C₅H₅Re(CO)Cl₂]⁺ [Re(CO)₄Cl₂]^–, and -C₅H₅Re(CO)₂I₂, the latter of which was separated into the cis and trans isomers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimlcheskaya, No. 2, pp. 408–413, February, 1981.The authors express their gratitude to V. F. Sizom, P. V. Petrovskii, and B. V. Lokshin for taking the mass, IR, and PMR spectra.     

π -Type and σ -type cation- π complexes of atomic cations

MP2/6-31+G* calculations were performed on the cation- complexes of ethylene, cyclobutadiene and benzene with a number of atomic cations. It was found that except B⁺ all the atomic cations form -type cation- complexes with ethylene. On the other hand, with cyclobutadiene Li⁺, N⁺, Na⁺, P⁺ and K⁺ form -type complexes, whereas H⁺, F⁺, and Cl⁺ form covalent -type complexes. With benzene Li⁺, B⁺, Na⁺, Al⁺, and K⁺ form -type complexes whereas H⁺, F⁺, and Cl⁺ form -type complexes. It was concluded that the driving force to form the -type complex is chemical bonding, and that for metal cations to form -type complexes is non-covalent interaction.     

Molecular structure of mono- and dicarbonyls of rhodium and palladium

Summary Density Functional Theory has been applied to the study of the molecular structure of neutral and positively charged mono- and dicarbonyls of rhodium and palladium. The calculated optimized geometries, dissociation energies and normal frequencies are reported for the MCO, MCO⁺, M(CO)₂ and M(CO) ₂ ⁺ systems (where M=Rh and Pd), and the trends are discussed in detail. For neutral carbonyls, we interpret the M–C bond strength in terms of repulsion, which must be avoided, and attraction. These are related to the metal atom properties, such as the atomic splittings and the atomic ionization energies. In ionic carbonyls, the bonding is characterized by electrostatic attraction and repulsion. The rhodium carbonyls are generally found to be more stable than the corresponding palladium carbonyls. The palladium dicarbonyls are found to be linear, while both linear and bent structures are stable for rhodium dicarbonyls. An interpretation of these trends is made.     

On the possibility of existence of η4-π-complexes of corannulene (C20H10) and Ñ60 fullerene derivatives

The problem of existence of ⁴--complexes of transition metal atoms with Ñ₆₀ fullerene and its simplest bowl-shaped hydrocarbon precursor, corannulene (Ñ₂₀H₁₀), is discussed in the framework of the HF/3-21G and DFT/TZ2P methods. The molecular structures of corannulene and Ñ₆₀ fullerene derivatives, namely, C₂₀H₁₄, C₂₀H₁₆, C₆₀H₄, and C₆₀H₆ were simulated. These molecules can form stable ⁴--complexes C₂₀H₁₄Fe(CO)₃, C₂₀H₁₆Fe(CO)₃, C₆₀H₄Fe(CO)₃, and C₆₀H₆Fe(CO)₃ in which the Fe atom interacts with C atoms of a fulvene-like or butadiene-like conjugated fragment of the hydrocarbon ligands. The energies of the ⁴--bonds in the complexes under study were compared with the corresponding bond energies in the classical complexes C₄H₆Fe(CO)₃ and C₅H₆Fe(CO)₃. The geometric parameters of C₄H₆Fe(CO)₃ and C₅H₆Fe(CO)₃ obtained from DFT calculations are close to the experimental values. Stabilities of the ⁴--complexes studied and their ⁵--analogs were compared.     

The Effect of cis-trans Isomerism on the Electronic-vibrational Structure of the Ground and Excited States and Reactivity of 2-(2-Furyl)- and 2-(2-Thienyl)oxazole

The fluorescent properties, structure, and electronic structure of the ground and excited singlet and triplet electronic states of the cis and trans forms of 4,5-dihydro-2-(2-furyl)oxazole, 4,4-dihydro-2-(2-thienyl)oxazole, 2-(2-furyl)oxazole (FO), and 2-(2-thienyl)oxazole (TO) have been studied. The orbital nature of the lower excited singlet and triplet states has been studied by the semiempirical INDO/S (valence approximation) and PPP/S ( approximation) methods. It was shown that for FO and TO molecules the lower triplet state is of the * type, for which delocalization of the electronic excitation on atoms is characteristic. In the singlet excitation state inversion was observed of the energy levels of the delocalized * states and n* states localized over several bonds (for the free TO and FO molecules the lower excited singlet states S₁* were assigned to * and n* types respectively). Owing to the low position of the T * and T _n* levels relative to the singlet level of * type, the rate constant for intercombination conversion is greater than the rate constant for radiative decay. Consequently an efficient population of the triplet states of the molecules occurs under conditions of electronic-vibrational excitation. The direction of reactions during synthesis was compared with the localization indices in the ground state for electrophilic, nucleophilic, and radical substitution, and also with the excitation localization numbers L for a wide selection of electronically excited states. It was concluded that the change in the structure of the azole molecule on replacing an O atom by an S atom, or on changing from a partially hydrogenated to a heteroaromatic system, was the main reason for the change of all the spectral parameters characterizing the electronic-vibrational or the spin-orbital interaction of the most reactive groups of atoms in the molecular structure.     

Stereochemistry of the synthesis of 1,2,3,4-tetrahydrocinnolines from aryldiazenium salts and olefins

It follows from the PMR spectra that the reaction of 1-methyl-, 1-phenyl-, 1-ethyl-,1-phenyl-, and 1,1-diphenyldiazenium salts with cis- and trans-d-styrenes, which leads to the corresponding 3-d-4-phenyl-1,2,3,4-tetrahydrocinnolines, takes place with retention of the configuration in the starting styrenes. It is therefore proposed that this reaction be regarded as a special case of [4⁺_s + 2_s]-cycloaddition.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1658–1661, December, 1977.     

Excited Π states of divinyl chalcogenides and chalcophenes

Electron transitions in divinyl chalcogenides (CH₂=CHXCH=CH₂, where X is S, Se, or Te) have been analyzed using UV absorption spectra of dialkyl and alkyl vinyl chalcogenides. The following relations for the orbital energies are found: ^* < ^* < ^* < ^* for Te and ^* < ^* < ^* < ^* for S and Se. For chalcophenes, a correlation between the energy of the excited state (E ^*) of specific symmetry, the ionization potential (I) and the electron affinity (EA) is obtained:E ^*=const+(I+EA)/2. The electron affinity of divinyl chalcogenides is estimated. The correlation between the excited ^* states of divinyl chalcogenides and chalcophenes is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–835, May, 1994.     

Electronic Structures, (d-p)π Conjugation Effects, and Spectroscopic Properties of Polyoxometalates: M6O19 2− (M=Cr, Mo, W)

The electronic structures and bonding of isopoly oxometalates M₆O₁₉ ^2– (M=Cr, Mo, W) have been investigated by using ab initio and relativistic density functional methods. We have discussed the role of the central oxygen atom and the (d-p) conjugation interactions between the metal and bridging oxygen atoms. It is found that there exist 12 three-centered two-electron (d-p-d) bonds for the three M₄(-O)₄ planar rings in M₆O₁₉ ^2– ions and these hexametalates are considered to have quasi-aromaticity. The (d-p) conjugation effects play essential role in stabilizing these cluster compounds, and the reduced (d-p) conjugation effects account for the instability of the isopoly oxochromate ion, Cr₆O₁₉ ^2–. The vibrational spectra and electronic spectra of M₆O₁₉ ^2– ions are evaluated and assigned theoretically and the calculated spectra are in fairly good agreement with the measured experimental results.     

Ab initio SCF and CI study of the electronic spectrum of pyridine N-oxide

Configuration interaction (CI) studies of ground, n *, * * electronically excited states are reported for pyridine N-oxide. The transition energy to the lowest * excited ¹ B ₂ state is calculated at 4.35 eV, compared to the experimental spectrum range of 3.67–4.0 eV. This state lies below the lowest n * excited ¹ A ₂ state calculated at 4.81 eV above the ground state. The only experimentally reported triplet state at 2.92 eV above the ground state is predicted to be the ³ A ₁ (*) state. The calculated energy lies at 3.27 eV. Numerous other high-lying singlet states as well as the triplet states have also been calculated. The intramolecular charge transfer character of the ground and the excited states have been studied in terms of the calculated dipole moment and other physical properties.     

A 2pπ, 3dπ valence bond wave function for the 1B1u state of ethylene

A 2p, 3d valence bond wave function for the lowest ¹ B _1u state of the -system of ethylene is variationally optimized with respect to the atomic orbital exponents using a non-empirical -approximation. The resulting energy compares favourably with previous calculations and leads to a satisfactory value for the lowest ¹ A _1g-¹ B _1u transition energy. The optimized exponent for the 2p orbital is close to the Slater value whereas the exponent for the 3d orbital is found to be nearly hydrogenic. The implications of this result are discussed in some detail.

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Zusammenfassung Für den tiefsten ¹ B _1u -Zustand des -Elektronensystems des Äthylens wird nach der Variations-methode eine 2p, 3d-Valenzbindungs-Wellenfunktion bezüglich der Orbitalkoeffizienten optimiert, wobei eine nicht-empirische -Approximation zugrunde gelegt wird. Die berechnete Energie stimmt gut mit den Ergebnissen vorausgegangener Rechnungen überein. Für den tiefsten ¹ A _1g ¹ B _1u -Übergang ergibt sich ein befriedigender Energiewert. Der optimierte Orbitalkoeffizient für das 2p-Orbital stimmt gut mit dem nach der Slaterschen Regel bestimmten Koeffizient überein, während man für den 3d-Orbitalkoeffizienten einen Wert findet, der dem des Wasserstoffs ähnlich ist.

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Résumé Une founction d'onde V.B.(2p , 3d ) est optimée pour l'état ¹ B _1u d'aethylen. L'energie calculé aussi que l'energie de transition la plus basse ¹ A _1g -¹ B _1u est en bon accord avec des valeurs connues.

     

Synthesis of 2,3,4,6,7,8-Hexahydro-5H-1-benzopyran-5-ones and 3-(6-Oxo-1-cyclohexenyl)alkanoic Acids by Reduction of 4,6,7,8-Tetrahydro-2H-1-benzopyran-2,5(3H)-diones

Comparative results on the reduction of 4,6,7,8-tetrahydro-7,7-dimethyl-2H-1-benzopyran-2,5(3H)-diones 1 are reported. Hydride reduction (LiAlH₄ in Et₂O or NaBH₄ in i-PrOH) affords 2,3,4,6,7,8-hexahydro-5H-1-benzopyran-5-ones 5 in 30-60% isolated yield. Photochemical reduction of 1b and 1d (direct irradiation at λ = 300 or 254 nm in i-PrOH, or sensitized irradiation in acetone/i-PrOH or benzene/i-PrOH) gives 3-(6-oxo-1-cyclohexenyl)alkanoic acids 6 in 50–80%, while 1c affords the isomeric 3-(4,4-dimethyl-6-oxo-1-cyclohexenyl)-4-methyl-4-pentenoic acid ( 9 ) in 73% isolated yield. Electrochemical reduction (Hg, CH₃CN, Bu₄N⁺ClO, ?2.6 V vs. Ag/Ag⁺) requires more than 4 Farad/mol for the consumption of 1 without any major product being detected.     

The influence of pentaamminerhodium(III) on the1H n.m.r. spectra and pyrrole pKas of coordinated imidazoles and pyrazoles

Summary The following [(NH₃)₅RhLH]Cl₃ salts were preparedvia the [(NH₃)₅Rh(O₃SCF₃)](O₃SCF₃)₂ synthetic route; LH=1-methylimidazole (1CH₃imH), 2-methylimidazole (2CH₃imH), 4-methylimidazole (4CH₃imH), 5-methylimidazole(5CH₃imH), and pyrazole (pyzH). pK_a's at 25.0°C were determined for [(NH₃)₅RhLH]³⁺ complexes as follows: 2CH₃imH, 10.4±0.1; 5CH₃imH/4CH₃imH isomer mixture, 10.3±0.1; pyzH, 6.54±0.05. The influence on the pK_a's of imidazoles is dominated by withdrawal of the rhodium(III) centre and may be compensated by the presence of ring methylation by only 0.5log units for cobalt(III) and rhodium(III) derivatives, compared to 1.3 units for the -withdrawing ruthenium(III) centre. In the case of the -acceptor pyrazole ring, [(NH₃)₅Rh]³⁺ is observed to serve as a slight -donor and raises the pK_a above the cobalt(III) analogue. The¹H n.m.r. spectra of [(NH₃)₅RhLH]³⁺ complexes of the substituted imidazoles and pyrazole exhibit a deshielding order. C–2H>C–5H>C–4H for imidazoles and C–3H>C–5H>C–4H for pyrazole, as do their cobalt(III) analogues. The magnitude of values (=_{free L}-_complex) are virtually the same as in the cobalt(III) systems which shows that TIP influences are unimportant compared to ring rehybridization in estabilishing chemical shifts for both the cobalt(III) and rhodium(III) complexes. The imidazolato and pyrazolato complexes exhibit resonances upfield of the respective substituted imidazole or pyrazole complex in keeping with more negative charge on the rings; the influence is largest at C–2H of imidazolates and C–3H of pyrazolate.     

Norbornadiene complexes of transition metals 1. Synthesis of Rh(η4-C7H8)(η5-C5H5) derivatives with functional substituents in the diene ligand

Conclusions New rhodium complexes, derivatives of Rh( ⁴-C₇H₈)(acac) and Rh( ⁴-C₇H₈)( ⁵-C₅H₅) with functional groups in the norbornadiene ligand, have been synthesized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1124–1127, May, 1981.     

Homodimerization of spiro{bicyclo[2.2.1]Hepta-2,5-Diene-7,1′-cyclopropane}, catalyzed by group VIII transition metal complexes

Conclusions The homodimerization of spiro{bicyclo[2.2.1]hepta-2,5-diene-7,1-cyclopropane} (I) has been investigated in the presence of Ni-, Fe-, Co-, Rh-, and Ir-based metal complex catalysts. Depending on the nature of the metal and its ligand environment cyclodimerization of (I) can take place via [2+2]-, [2+2+2]-, and [4+4]-cycloaddition schemes, to give high yields of hepta-, octa-, and nonacyclic strained hydrocarbons.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2592–2599, November, 1988.     

Investigation of the reaction of acetone and acetonitrile molecules with the surfaces of metallic catalysts by IR-spectroscopic and quantum chemical methods

IR-spectroscopic and quantum chemical methods have been used to establish that the preferred form of the bonds of acetone and acetonitrile with transition metals are by dative action, in which the d-electrons of the metal are localized on the antibonding ^*-orbitals of the functional groups of these molecules. During adsorption of (CH₃)₂CO it is also possible to form a donor-acceptor complex, when there is a transfer of -electrons from the ketone molecule to the free dorbital of the metal.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 545–552, September–October, 1988.     

An electroanalytical investigation of the olefin isomerization reaction promoted by electrogenerated cationic nickel(I) complexes

Summary Evidence for the ability of the electrogenerated cationic nickel(I) complex [Ni(PPh₃)₄]⁺ to promote the isomerization of allylbenzene is reported. However, the corresponding triethylphosphitenickel(I) complex displays no catalytic activity, apparently due to the poor leavinggroup character exhibited by the phosphite. The involvement of a -allylnickel hydride in the isomerization reaction is inferred from a comparison of the results obtained with those for the same reaction promoted by nickel hydride.     

2,5-Dimethylthiophene coordination to three metal centers in the complexes (η4, S-μ3-2,5-Me2T)(IrCp*) [M(CO)2Cp]2 where MMo or W

The 2,5-dimethylthiophene (2,5-Me₂T) ligand in the isomers Cp*Ir(η⁴-2,5-Me₂T) (1) and Cp*Ir(C,S-2,5-Me₂T) (2) is activated to react with the dimers Cp(CO)₂M?M(CO)₂Cp[M?Mo (3), W (4)] to give complexes (5,6) in which the thiophene is coordinated to three metals. Oxidation of 5 with Cp₂Fe⁺ removes the Mo dimer to give Cp*Ir(η⁵-2,5-Me₂T)²⁺. Reaction of 5 with CO displaces the Mo as [CpMo(CO)₃]₂ to give Cp*Ir(CO)(C,S-2,5-Me₂T) (7). Ultraviolet photolysis of 1 provides a convenient route to the ring-opened isomer 2. Despite the remarkable nature of the thiophene coordination in 5 and 6, its reactivity does not suggest new pathways that would lead to the hydrodesulfurization of thiophenes.     

Solvent effects on the asymmetric Pauson-Khand-type reaction by rhodium

The reaction efficiency and enantioselectivity of an asymmetric Pauson-Khand-type reaction catalyzed by cationic rhodium are heavily dependent on the solvent. Coordinating solvents, such as THF, provide a faster reaction and better stereoselectivity than non-coordinating solvents, such as toluene. These beneficial effects can be attributed to a significant increase in the more reactive catalytic species of [Rh(bisphosphane ligand)^∗(solvent)_n]⁺ (3) than of [Rh(bisphosphine ligand)^∗CO(solvent)]⁺(4) and [Rh(bisphosphine ligand)∗(CO)₂]⁺ (5) in a coordinating solvent.