RESUMO
A new pentanuclear "cylinder"-like cobalt(ii) phenylsilsesquioxane [(PhSiO1.5)10(CoO)5(NaOH)] exhibits a slow relaxation of the magnetization and a high catalytic activity and stereoselectivity in the oxidation of alkanes and alcohols.
RESUMO
A series of glutarimide derivatives which has two carbonyl coordination sites for intramolecular pentacoordination at silicon with a X(1+n)SiC(3-n)O moiety have been synthesised and characterized. The substituent (leaving group) effects on the Si-O bond exchange between the two coordination sites (resembling a pendulum) have been studied by comparison of the differently substituted (X = F, Cl, OTf, Br and I) structures. The activation parameters for the Si-O bond exchange process were measured by NMR and separately computed and are consistent with the strength of Si-O bond coordination and the nature of the leaving group, X. The temperature-dependent (29)Si NMR spectroscopy is supported by X-ray crystallography and shows that the tetrahedral reactant is converted into pentacoordinate intermediates by intramolecular O-Si association followed by reversion to a tetrahedral geometry by Si-X dissociation. The two association/dissociation patterns offer a model for nucleophilic substitution at a silicon atom. A continuum of structures on the S(N)2 reaction profile from the glutarimide derivatives correlates reasonably well with the structural data obtained from derivatives of lactams, diketopiperazines and quinolones.
RESUMO
The crystal structure of [C(n)mim]NTf(2) (n = 2, 4, 6) was studied for the first time simultaneously by X-ray diffraction method and IR spectroscopy. The temperature-dependent IR spectrum for crystalline [C(4)mim]NTf(2) was demonstrated to correlate with both the X-ray data and the calorimetric results obtained earlier. Therefore, it was found that IR spectroscopy is able to establish the correspondence between the X-ray and the calorimetric data in this case. The joint use of X-ray diffraction, IR spectroscopy, and quantum-chemical calculations allowed us to determine the structure of all [C(2)mim]NTf(2) crystalline modifications obtained earlier by adiabatic calorimetry measurements. Thus, a new approach for the future identification of ionic liquid crystal structure by use of temperature-dependent infrared spectroscopy is suggested and justified.
RESUMO
On the basis of high-resolution X-ray diffraction studies as well as quantum-chemical calculations of five carborane derivatives the peculiarities of electron density distribution functions have been analyzed. The data obtained permitted a deeper insight into the nature of unusual properties of the C-C bond in o-carborane and investigating intermolecular H ... H interactions in crystal. It was shown that such an approach allows estimating the values of lattice energy for the crystals of carboranes.
RESUMO
The first carborane triflates, namely, 1-trifluoromethanesulfonylmethyl-o-carborane (2) and 1,2-bis(trifluoromethanesulfonylmethyl)-o-carborane (7), were obtained in high yields in the reactions of 1-hydroxymethyl-o-carborane (1) or 1,2-bis(hydroxymethyl)-o-carborane (6) with triflic anhydride (Tf2O) in CH2Cl2 in the presence of pyridine. When an excess of pyridine is employed, 1-o-carboranylmethylpyridinium triflate (3), which retains a closo-icosahedral structure, or a pyridinium salt (4) with a zwitterionic nido-dicarbaundecaborate anion are obtained from 1, while the nido compound 8 is formed from 6. The reaction of compound 2 or 7 with excess pyridine also gave 3 or 8, respectively. Compound 2 proved to be a convenient carboranylmethylating agent which reacts with nucleophiles (e.g., potassium phthalimide, PPh3 or KCN) to give the corresponding substitution products N-[(o-carboranyl-1-yl)methyl]phthalimide (9), o-carboranylmethylphosphonium salt 10, and 1-cyanomethyl-o-carborane (11). All compounds were characterized by 1H and 11B NMR spectroscopy. The structures of compounds 4, 7 and 8 were established by X-ray analysis.
