Evgenii V. Vorontsov

NMR evidence for formation of new alcohol rhenium complexes as intermediates in ionic hydrogenations of carbonyl groups with systems composed of ReH2(NO)(CO)(PR3)2 (R = Pri, CH3, OPri) and CF3COOH

Low-temperature hydrogenations of benzaldehyde and acetone by systems ReH2(CO)(NO)(PR3)2/CF3COOH in CD2Cl2 with R = Pri (1a), CHa (1b) and OPr1 (1c) result in formation of the new unstable alcohol complexes [ReH(CO)(NO)(PR3)2(R∗OH)] [CF3COO] (R∗C6H3CH2, (CH3)2CH) characterized by the low-temperature NMR spectra. Heating the reaction solutions above 210–240 K leads to alcohol elimination to form monohydrides ReH(CO)(NO)(PR3)2(CF3COO). Hydrogenation rates decrease in the order 1b > 1c > 1a and C6H5CHO > (CH3)2CO. Hydrogenation processes remain effective under H2 (or D2) atmosphere and in the presence of an excess of CF3COOH when the dihydrides exist as dihydrogen compounds [ReH(H2)(CO)(NO)(PR3)2]1 [CF4COO], Relative acidity of the dihydrogen complexes decreases in the order OPr1 > Pr1 > CH3. The hydrogenation with dihydrogen complexes is discussed in terms of an ionic mechanism.

New aromatizational transformations of 4-methyl-4-trichloromethyl-substituted 2,5-cyclohexadiene triphenylphosphonium and pyridinium ylides: Abstraction or 1,6-migration of the CCl3 group

Abstract4-methyl-4-trichloromethylcyclohexadiene triphenylphosphonium ylide obtained by treatment of (1-methyl-1-tricholoromethylcyclohexa-2,4-dien-4-yl)-triphenylphosphonium bromide with BunLi in THF is stabilized by the abstraction of the CCl3 group to give (p-tolyl)triphenylphosphonium cation, which was isolated as the corresponding hydroxide. Conversely, an analogous pyridinium ylide, obtained by treatment ofZ/E stereoizomericN-(1-methyl-1-trichloromethylcyclohexa-2,5-dien-4-yl)pyridiunium bromide with a base (piperidine in CD2Cl2, BunLi in THF), at temperatures above −40 °C, undergoes a novel high-yield aromatizational skeletal rearrangement with migration of the CCl3 group to position 2 of the heterocycle.

Synthesis and aromatizational rearrangements of new imino-, hydrazono-, and azino-2,5-cyclohexadienylidene systems as ligands for cascade type metallocomplexes

Three approaches to the synthesis ofN-substituted imino-, hydrazono-, and azino-2,5-cyclohexadienylidene systems based on reactions of 4-methyl-4-trichloromethylcyclohexa-2,5-dienone with aminophenols and hydrazones and condensation of hydrazones ofpara-semiquinoid ketones with carbonyl compounds, including that of the ferrocene series, were realized. The latter reaction, when applied to 3,6-dibromophenanthrene-9, 10-quinone, was accompanied by quantitative aromatizational molecular rearrangement with the elimination of the CCl3 group. Using Rh1 complexes as an example, it was shown that the heteroorganic ligands obtained can be used for the synthesis of mixed-ligand metallocomplexes with triple coordination of the metal atom including simultaneous metal-ligand interactions of the n-, π-, and σ-types.