Three isomers of yttrium carbide (Y 2 C 2 ) endohedral metallofullerenes, i.e., (Y 2 C 2 )@C 82 (I, II, III), have been synthesized and chromatographically isolated for the first time. The structures of (Y 2 C 2 )@C 82 (I, II, III) metallofullerenes have been characterized by 13 C NMR measurements, whose molecular symmetries have been determined to be C s , C 2V , and C 3V , respectively. In addition, a pure diyttrium metallofullerene, Y 2 @C 82 (III), has also been synthesized and structurally characterized. The 13 C NMR structural analyses indicate that (Y 2 C 2 )@C 82 (III) has exactly the same fullerene cage as that of Y 2 @C 82 (III). On the basis of the results, we propose a C 2 -trapping and loss of growth mechanism of dimetallofullerenes of (M 2 C 2 )@C 82 and M 2 @C 82 from M 2 @C 84 , respectively.

No abstract

No abstract

A synthetic route to enantiomerically pure (1R,2S)-1-phenylphospholane-2-carboxylic acid (1), which is a phosphorus analogue of proline, has been established. A key step is the deprotonation-carboxylation of the 1-phenylphospholane borane complex 3 by using sBuLi/1,2-dipiperidinoethane (DPE). Configurational stability of the key intermediate, the amine-coordinated alpha-phosphinoalkyllithium borane complex 4, was investigated by employing lithiodestannylation-carboxylation of both diastereomers of the 1-phenyl-2-trimethylstannylphospholane borane complex 7 in the presence of several kinds of amines, and as a result, 4 was found to be configurationally labile even at -100 degrees C. The key intermediate, the DPE-coordinated trans-1-phenyl-2-phospholanyllithium borane complex 9, was isolated, and the structure was identified by X-ray crystal structure analysis. This is the first X-ray crystal structure determined for an alpha-monophosphinoalkyllithium borane complex. Remarkably, the alkyllithium complex is monomeric and tricoordinate at the lithium center with a slightly pyramidalized environment, and the existence of a Li--C bond (2.170 A) has been confirmed. Moreover, (1)H-(7)Li HOESY and (6)Li NMR analyses suggested the structure of 9 in solution as well as the existence of an equilibrium between 9, its cis isomer, and the ion pair 8 at room temperature, which was extremely biased towards 9 at -100 degrees C. Finally, 1 was used as a chiral ligand in a palladium-catalyzed allylic substitution, and the desired product was obtained in high yield with good enantioselectivity.