42083-48-7Relevant academic research and scientific papers
Experimental and theoretical investigation of the enantiomerization of Lithium α-tert-butylsulfonyl carbanion salts and the determination of their structures in solution and in the crystal
Scholz, Roland,Hellmann, Gunther,Rohs, Susanne,Raabe, Gerhard,Runsink, Jan,Oezdemir, Diana,Luche, Olaf,Hess, Thomas,Giesen, Alexander W.,Atodiresei, Juliana,Lindner, Hans J.,Gais, Hans-Joachim
, p. 4559 - 4587 (2010)
Dynamic NMR (DNMR) spectroscopy of [R1C(R2)SO 2R3]Li (R1, R2 = alkyl, phenyl; R3 = Ph, tBu, adamantyl, CEt3) in [D8]THF has shown that the S-tBu, S-adamantyl, and S-CEt3 derivatives have a significantly higher enantiomerization barrier than their S-Ph analogues. C α-S bond rotation is most likely the rate-determining step of the enantiomerization of the salts bearing a bulky group at the S atom and two substituents at the Cα atom. Ab initio calculations on [Me(Ph)- SO 2tBu]- gave information about the two Cα-S rotational barriers, which are dominated by steric effects. Cryoscopy of [R1C(R 2)SO2tBu]Li in THF at -108°C revealed the existence of monomers and dimers. X-ray crystal structure analysis of the monomers and dimers of [R1C(R2)SO2tBu]Li·L n (R1 = Me, Et, tBuCH2, PhCH2, tBu; R2 = Ph, L = THF, 12-crown-4, PMDTA) and [R1C(R 2)SO2Ph]Li·2diglyme [R1 = R2 = Me, Et; R1-R2 = (CH2)5] showed them to be O-Li contact ion pairs (CIPs). The monomers and dimers have a Cα-S conformation in which the lone-pair orbital at the Cα atom bisects the O-S-O angle and a significantly shortened Cα-S bond. The Cα atom of [R1C(R2)SO2R 3]Li·Ln (R1 = Ph; R3 = Ph, tBu) is planar, whereas the Cα atom of [R1C(R 2)SO2R3]Li·Ln (R1 = R2 = alkyl) is strongly pyramidalized in the case of R3 = Ph and most likely planar for R3 = tBu. Ab initio calculations on [MeC- (Me)SO2R]- gave a pyramidalized Cα atom for R = Me and a nearly planar one for R = CF3 and tBu. The [R1C(R 2)SO2-tBu]Li salts were characterized by 1H, 13C, and 6Li NMR spectroscopy. 1H{ 1H} and 6Li{1H} NOE experiments are in accordance with the existence of O-Li CIPs. 1H and 13C NMR spectroscopy of [R1C(R2)SO2tBu]Li in [D 8]THF at low temperatures showed equilibrium mixtures of up to five different species being most likely monomeric and dimeric O-Li CIPs with different configurations. According to 7Li NMR spectroscopy, the addition of HMPA to [MeC(Ph)SO2tBu]Li in [D8]THF at low temperatures causes the formation of the separated ion pair [MeC(Ph)SO 2tBu]Li(HMPA)4.
