PMDTA

Abstract: Substituted 5-hexen-1-yllithiums, which were prepared in solutions of n-C 5 H 12 -Et 2 O (3:2 by vol) by low-temperature lithium-iodine exchange between t-BuLi and the appropriate iodide, undergo clean, 5-exo-trig cyclization upon warming to give substituted (cyclopentyl)methyllithiums, in good yield and with a high degree of stereocontrol. In each case, the major product is the same isomer as that observed in studies of the isomerization of analogously substituted 5-hexen-1-yl radicals, but the organolithium cyclizations are invariably much more stereoselective than radical-mediated processes. Lewis base additives such as THF, TMEDA, and PMDTA serve to increase the rate of cyclization of the substituted 5-hexen-1-yllithiums, but such additives do not reduce the high stereoselectivity of the process. The observed regioselectivities and stereoselectivities of the intramolecular addition of a C-Li bond to an unactivated alkene suggest that the closure of the anion proceeds via a transition state that resembles a chair cyclohexane in which substituents preferentially occupy pseudoequatorial positions

Abstract: The first Sr hydride complex has been obtained by simply reacting Sr[N(SiMe3)2]2 with PhSiH3 in the presence of PMDTA. The Sr complex Sr6[N(SiMe3)2]3H9∙(PMDTA)3 crystallizes as an "inverse cryptand": an interstitial Hˉ is surrounded by a Sr6H84+ cage decorated with amide and PMDTA ligands. The analogue Ca complex could also be obtained and both retain their solid state structures in solution: 1H NMR spectra in C6D6 show two doublets and one nonet (4:4:1). Up till 90 °C, no coalescence is observed. The Ca cluster was investigated by DFT calculations and shows atypically low charges on Ca (+1.14) and H (-0.59) which signifies an unexpectedly low ionicity. AIM analysis shows hydride∙∙∙hydride bond paths with considerable electron densities in the bond critical point. The clusters thermally decompose in larger, undefined, metal hydride aggregates.

Abstract: Mixtures of SmI2/H2O/amine have been found to reduce alkyl halides more efficiently than SmI2/HMPA/alcohol mixtures at room temperature. Alkyl and aryl iodides were quantitatively reduced in <1 min and alkyl bromides in 10 min, while alkyl and aryl chlorides required more than 5 h for completion. Determination of the reaction order of Et3N in the reduction of 1-chlorodecane showed that the reaction order is one. Water was shown not to participate in the rate-determining step of this reduction. There was a significant change of the UV−vis spectrum and color of SmI2 upon addition of either PMDTA or water, while no effect was observed with the addition of Et3N or TMEDA. Although the combination of SmI2, water, and amines produces a very efficient reducing system, cyclic voltammetric experiments showed that the redox potential is nearly identical with that of SmI2 alone. These results are consistent with precipitation providing the driving force for reduction. Taken together, the results of these experiments ...