IR spectroscopy and quantum-chemical calculations (B3LYP/6-31G*) were used to show that N-methyltrifluoromethanesulfonamide in the gas phase and in a low-polarity inert solvent (CCl 4 ) exists as an equilibrium mixture of monomers and cyclic dimers. In a more polar solvent (CH 2 Cl 2 ), highly polar openchain dimers are stabilized.According to X-ray diffraction data, methanesulfonamide molecules in crystal are hydrogen-bonded to form infinite tapes [1] and are not associated in highly dilute CCl 4 solutions (IR spectral data [2]). At the same time, N-substituted sulfonamides in an inert medium exist as equilibrium mixtures of monomers and cyclic dimers [235]. Perfluoroalkyl substitution in sulfonamides much enhances their acidic properties. For example, trifluoromethanesulfonamide is much more acidic (pK a 6.39 [6]) than phthalimide (pK a 9.9) and even alloxan [2,4,5,6(1H,3H)-pyrimidinetetrone, pK a 6.64] or thiophenol (pK a 6.5). Such a high NH acidity results in that trifluoromethanesulfonamide self-associates exist in the gas phase up to 440 K. According to IR spectral data and ab initio quantumchemical calculations, these are trimers and cyclic dimers [7]. N-Methyl substitution slightly reduces the acidity, but N-methyltrifluoromethanesulfonamide (I) is still fairly acidic (pK a 7.56 [8]).Carboxamides in the solid state, too, are polymeric associates linked by hydrogen bonds of different type, but, unlike sulfonamides, they do not form associates in highly dilute solutions and in the gas phase. Thus, in terms of the structure of self-associates, sulfonamides are closer to carboxylic acids which form cyclic dimers in inert media even at high temperatures. However, in terms of the stability of cyclic dimers, these two classes of compounds differ substantially. The formation heats of carboxylic acid associates are 10315 kcal mol !1 [9], whereas those of N-substituted alkane-and benzenesulfonamides are no higher than 234 kcal mol !1 [4]. Probably, the reason for this phenomenon consists in that the equilibrium mixture in more complex in composition than proposed in [4] and comprises not only cyclic but also open-chain associates. The question is only what is the position of the open-chain dimer 76 47 cyclic dimer equilibrium. Sulfonamide self-association is best studied by IR spectroscopy, and we made use of this method to study trifluromethanesulfonamide in the gas phase. Structural assessment of trifluromethanesulfonamide self-associates in solution is complicated by the intricate spectral pattern in the N3H stretching vibration region and the strong dependence of band shapes on the polarity of the medium. 1 Therefore, as the object for study we chose N-methyltrifluoromethanesulfonamide (I) whose IR spectrum in the 360033100 cm !1 range is simplified due to the presence of only one N3H bond.A density functional study (B3LYP/6-31G*) of Nmethyltrifluoromethanesulfonamide and its possible associates showed that the potential energy minima correspond to monomer I, as well as cyclic (IIa) and and open-chain (IIb) di...

The reaction of di µ chlorobis(1,5 cyclooctadiene)dirhodium with (4S,5S) 2,2 dimethyl 4,5 bis(methylaminomethyl) 1,3 dioxolane (1) gave the complex [Rh(cod)(1)]Cl (cod is 1,5 cyclooctadiene). The composition of the complexes CoCl 2 •L 2 and [Rh(cod)(L 2 )]X (L 2 = 1, (4S,5S) 2,2 dimethyl 4,5 bis(aminomethyl) 1,3 dioxolane, and (4S,5S) 2,2 di methyl 4,5 bis(dimethylaminomethyl) 1,3 dioxolane; X = Cl, TfO) was studied using IR and 1 H NMR spectroscopy. In the Rh I cyclooctadienediamine complexes, the diene molecule forms a stronger bond with the metal atom than that in the cyclooctadienediphosphine analogs.Transition metal complexes with chiral phosphines are efficiently used in the catalytic synthesis of optically active organic compounds. However, in recent years, con siderable attention has been devoted to transition metal complexes with N donor ligands, namely, amines and imines. These complexes are generally inferior to the phos phine analogs in the chirality transfer to the substrate and in the catalytic activity but are favorably distinguished by the relative simplicity of synthesis and stability against degradation under reductive conditions (in hydrogena tion with molecular hydrogen and in hydrogen transfer reactions). 1,2 In particular, C 2 symmetric Co II chloro diamine complexes CoCl 2 •L 2 (L 2 is (4S,5S) 2,2 di methyl 4,5 bis(methylaminomethyl) 1,3 dioxolane (1), (4S,5S) 2,2 dimethyl 4,5 bis(aminomethyl) 1,3 dioxo lane (2), and (4S,5S) 2,2 dimethyl 4,5 bis(dimethyl aminomethyl) 1,3 dioxolane (3)), which are structural analogs of the widely known diphosphine, (R,R) (-) 2,2 di methyl 4,5 bis(diphenylphos phanylmethyl) 1,3 dioxolane (4), have demonstrated 3 a mod erate chiral induction in the borohydride reduction of ac etophenone and esters of unsat urated acids: the optical yield of (S) 1 phenylethanol reached 24% ее and that of di methyl (S) α methylsuccinate was 37.5%. In the cata lytic hydrogenation of acetophenone with hydrogen trans fer from isopropanol on rhodium chloride and triflate complexes with diamines, [Rh(L 2 ) 2 ]X and [Rh(L 2 )(cod)]X (L 2 = 2, 3; Х = TfO, Cl), in the presence of KOH and Bu t OK, the optical yield of S(-) 2 phenylethanol was 67%. 4 The catalytic activity and the stability of transition metal complexes in solution are determined by numerous factors, in particular, by the nature and the spatial struc ture of the ligands. Previously, we demonstrated 4 that primary diamine 2 and tertiary diamine 3 form rhodium complexes of different compositions. Therefore, it ap peared of interest to try using secondary diamine 1 as the ligand. In this study, we prepared a new rhodium cyclo octadiene chloride complex with diamine 1 and com pared characteristics of the Co II and Rh I complexes with diamines 1-3 by IR and NMR spectroscopy. Results and DiscussionCo II complexes with diamines 1-3. Complexes 5a-c CoCl 2 •L 2 (L 2 = 1 (a), 2 (b), 3 (c)) were prepared by the reaction of equimolar amounts of anhydrous CoCl 2 and diamines 1-3 in dichloromethane. The metal : ligand ratio in the comp...

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The equilibrium torsion angles of 2-arylpyrroles in the liquid and solid phases were estimated by UV spectroscopy. In solution, compounds comaining no substituents in positions I, 3, and 2" possess an average torsion anne of 24 ~ those containing one substituent have an angle of 29 ~ and in the case of two and three substituents, the angles are 53 ~ and 65 ~ respectively. Phase transitions lead to tlattenmg of the molecules ha almost all cases. The average torsion angles in the compounds with no substituents in positions 1, 3, and 2" decrease by -5 ~ on passing from the gas to the liquid state and by -25 ~ on going from the liquid to the solid state. The geometric parameters of 2-arylpyrroles with one or two substituents in positions 1, 3, and 2" axe less sensitive to phase transitions, while trisubstituted derivatives even retain their equilibrium conformations upon phase transitions.Key words: equilibrium conformation of molecules, UV spectroscopy, semiempirical MO calculations, 2-arylpyrro[es.Of conformationaily mobile molecules with extended r~-systems, diphenyl and its derivatives have been structuraUy studied in greatest detail The equilibrium geometry of these compounds depends markedly on the nature of the substituents and on the physical state. For example, the equilibrium torsion angle in diphenyl varies from 44 ~ in the gas phase I to 30 ~ (or 20~ 2'3 in the hquid phase and to 0 ~ in the cr~3tal. 4 The conformations of a fairly large number (-20) of diphenyl derivatives having no substituents in the ortho-positions of the phenyl groups are susceptible to similar influences. 5 This is due to the fact that rotation of phenyl groups requires relatively little energy, which can be made up by intermolecular interactions. 6 The conformations of other linked cyclic systems also depend on the physical state. One of the few known examples of this dependence is 3,3 "-dithienyl, whose equilformm torsion angle is 30 ~ in the gas phase, 7 22 ~ in the nematic phase, s and 0 ~ in the crystal. 9 Structural studies of the vast majority of compounds of the diphenyl type have been carried out for one of the physical states, l~In particular, we determined the equilibrium torsion angles for a series of 2-phenylpyrroles (2-PP) in the gas phase by photoelectron spectroscopy. 13-16 Almost all of these compounds were found to be non-planar. In the present work, the equih'brium conformations of 2-arylpyrroles in solution and in a solid matrix were studied by UV spectroscopy.+Deceased. ExperimentalElectronic absorption spectra were recorded on a Specord M-40 spectrophotometer at 22--25 ~C. The concentrations of compounds in hexane and acetonitrlle amounted to 10 -4-10 -3 tool L -l. The spectra in the solid phase were recorded in poly-(1-vinyi-2-methylimidazole) (PVMD films and in KCI discs. The first procedure makes it possible to obtain more precise information on the positions of long-wavelength bands (Fig. 1); addition of PVMI has no effect on the UV spectra of the compounds in solution. However, this procedure is inapplicabl...

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