B. V. Lokshin

Mechanistic Investigation of the Asymmetric Addition of Trimethylsilyl Cyanide to Aldehydes Catalysed by Dinuclear Chiral (Salen)titanium Complexes

Titanium complexes 1 derived from chiral salen ligands are highly active precatalysts for the asymmetric addition of trimethylsilyl cyanide to aldehydes and ketones. Based on spectroscopic studies and the identification of adducts between complexes 1 and carbonyl compounds or trimethylsilyl cyanide, a catalytic cycle which explains the origin of the asymmetric induction is proposed. Kinetics studies have been carried out, the results of which are consistent with the proposed catalytic cycle.

Protonation of metal carbonyl complexes : III. Cyclopentadienyl carbonyl complexes of manganese

Abstract Using IR spectroscopy, the phosphine derivatives of cyclopentadienylmanganese tricarbonyl have been shown to undergo protonation in solutions of trifluoroacetic acid and in mixtures of this solvent with methylene chloride, protonation at the metal atom being the most probable. Ease of protonation increases with increasing electron-releasing properties of both the π-ring substituents and the phosphine ligands attached to the manganese atom. The basicity of manganese in these cyclopentadienylmanganese tricarbonyl compounds is less than that of chromium in the corresponding benzenechromium tricarbonyl derivatives.

Protonation of metal carbonyl complexes : I. An infrared study of the arenechromium tricarbonyl and arenechromium dicarbonyl triphenylphosphine complexes

Abstract Through the use of IR spectroscopy, protonation of arenechromium dicarbonyl triphenylphosphine complexes in trifluoroacetic acid and in mixtures of the latter with methylene chloride, has been shown to occur at the metal atom. No protonation of arenechromium tricarbonyls appears to occur under similar conditions. The ease of protonation appears to increase with the introduction of increasing electron-releasing substituents into the π-bonded aromatic ring.

Basicity of transition metal carbonyl complexes: VIII. An infrared study of the reaction of aluminium chloride with some cyclopentadienyl and arenecarbonyl transition metal complexes

Abstract The interaction of cyclopentadienyl and arene derivatives of carbonyl complexes of Group V, VI and VII transition metals with AlCl 3 in benzene and CH 2 Cl 2 solutions has been studied by IR spectroscopy. The formation of adducts involving the metal atom or the carbonyl oxygen atom was observed. The reaction path depends on the structure of the complex and on the nature of the solvent. In benzene the adduct formation at the CO ligand is more favourable than in CH 2 Cl 2 solution. Introduction of a phosphine ligand in the place of the CO group or introduction of donor substituents into the π-ring increases the basicity of the central metal atom and makes adduct formation at the metal more probable. The basicity of the metal atom in complexes with the same ligands increases with increases of atomic number in the group. CpRe(CO) 2 Br 2 forms adducts with AlCl 3 at the bromine atoms ( 1 1 and sol1 2 ). For Fe(CO) 4 PPh 3 and Fe(CO) 3 (PPh 3 ) 2 complex formation takes place at the iron atom.

Vibrational spectra and structure of the cyclopentadienyl-anion (Cp−), the pentamethylcyclopentadienyl-anion (Cp*−) and of alkali metal cyclopentadienyls CpM and Cp*M (M=Li, Na, K)

Abstract Structural, electronical and vibrational properties of Cp − and Cp* − , and of alkali metal cyclopentadienyl (CpM, M=Li, Na, K) and pentamethylcyclopentadienyl (Cp*M, M=Li, Na) complexes have been studied. The main goals of the study were to investigate the influence of the CH 3 groups on the spectral features and on the MC force constants and the change of ionic character of the MC bond for different metals. FT-IR, FT-FIR and FT-Raman spectra of LiCp* and NaCp* compounds were recorded. Density functional theory calculations have been performed in order to obtain optimized geometries, vibrational frequencies and IR intensities. Calculated vibrational data were systematically compared to the experimental ones. Based on the calculations and experimental data, the vibrational spectra of Cp − and CpM were revised and reinterpreted, and a complete assignment of Cp* − and Cp*Li, Cp*Na vibrations was proposed. Correlations have been determined for the different metal atoms and the charge distribution, bond orders, bond energies and force constants.

Interaction of cyclopentadienyl carbonyl phosphine complexes of manganese with Lewis acids. Infrared Spectra

From IR-spectroscopic studies it is shown that phosphine derivatives of cyclopentadienylmanganese tricarbonyl interact reversibly with SnCl4 and another Lewis acids in CH2Cl2 solution. The structures of the resulting complexes are discussed. Complex formation is favoured as the electron-donor properties of both the π-ring substituents and of the phosphine ligands attached to manganese atom are increased. The ability of Lewis acids to undergo such complex formation follows the series: SnCl4 > SbCl3 > HgCl2 > GeCl4.

Vibrational spectroscopic and force field studies of (η5-Cp)ML3-type complexes (M=Mn, Re; L=CO, O)

Abstract High- and low-oxidation state CpML3-type (M=Mn, Re; L=O, CO) cyclopentadienyl complexes have been investigated by vibrational spectroscopy (FTIR, FT-FIR, FT-Raman) and normal coordinate calculations. The vibrational spectra of CpMn(CO)3, CpRe(CO)3 complexes were revised and reinterpreted. For the oxo-complexes and Cp*-carbonyl compounds, Cp*Mn(CO)3 and Cp*Re(CO)3, a complete spectral assignment is proposed. The results of the normal coordinate analysis are in good agreement with the spectral evidence. The vibrational spectroscopic findings help to explain earlier observations, e.g. the significantly lower stability of CpReO3 in comparison to Cp*ReO3. Characteristic force constants have been determined for Cp and Cp* ligands. A method is described for estimating an approximate force constant for the metal cyclopentadienyl (Cp) ligand bond stretch in half sandwich type of complexes, based on the use of an effective ‘spectroscopic’ mass of the Cp-ligand.

Analysis of vibrational spectra of naphthalene, deuterionaphthalenes, and chromium (η6-naphthalene)tricarbonyl based on density functional calculations

The vibrational frequencies and force constants for naphthalene (C10H8), 1,4,5,8- and 2,3,6,7-tetradeuterionaphthalenes (C10H4D4), octadeuterionaphthalene (C10D8), and chromium (η6-naphthalene)tricarbonyl were calculated by the DFT method using the PBE approximation in extended and split bases. The results calculated without the use of scaling factors are in good agreement with the IR and Raman experimental data. All vibrational frequencies for the free ligand and π-complex molecules were assigned. The influence of coordination to the transition metal on the frequencies and force field of the naphthalene molecule (both for the free ring and the ring coordinated to the transition metal) was discussed.

Vibrational spectra of tris(cyclopentadienyl)zirconium and -hafnium hydrides and deuterides, Cp3MX (M Zr, Hf; X H, D)

The synthesis has been performed of tris(cyclopentadienyl)hafnium hydride and deuteride from Cp4Hf treated with LiAlH4 and LiAlD4, respectively. The IR spectra (4000—100 cm-1) and Raman spectra of tris(cyclopentadienyl)zirconium and -hafnium hydrides and deuterides have been studied. The compounds are shown to have the structure (η5-C5H5)3MX (M  Zr, Hf; X  H, D) with three identically bonded cyclopentadienyl ligands. The spectral characteristics obtained are consistent with metal—ring coordination of the central type. An increase is noted in the strength of the M—H and M—Cp bonds when passing from zirconium to hafnium.

Study of the catalytic activity of electrochemically reduced forms of phthalocyanines in the reaction of CO2 with epoxides

Catalytic activity of electrochemically reduced forms of mono- and diphthalocyanine complexes of transition and rare-earth elements in the reaction of carbon dioxide with epoxides is considerably higher than that of corresponding neutral forms. The catalytic efficiency depends on the nature of the phthalocyanine complex, the method of the catalyst immobilization, and the electrophilicity of epoxide.