This title appears in the Scientific Report : 2010 

Experimental and Theoretical Study of the Enantiomerization Barrier of a-Sulfonyl Carbanions and Determination of the Structure of Lithium a-tert-blutylsulfonyl Carbanion Salts in Solution and the Crystal
Scholz, R.
Hellmann, G. / Rohs, S. / Raabe, G. / Raabe, G. / Runsink, J. / Özdemir, D. / Luche, O. / Heß, T. / Giesen, A.W. / Atodiresei, J. / Lindner, H.J. / Gais, H.-J.
Stratosphäre; IEK-7
European journal of organic chemistry, 2010 (2010) S. 4559 - 4587
Weinheim Wiley-VCH Verl. 2010
4559 - 4587
10.1002/ejoc.201000409
Journal Article
Atmosphäre und Klima
European Journal of Organic Chemistry 2010
J
Please use the identifier: http://dx.doi.org/10.1002/ejoc.201000409 in citations.
Dynamic NMR (DNMR) spectroscopy of [(RC)-C-1(R-2)SO2R3]Li (R-1, R-2 = alkyl, phenyl; R-3 = Ph, tBu, adamantyl, CEt3) in [D-8]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-alpha-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 C-alpha, atom. Ab initio calculations on [Me(Ph)SO(2)tBu](-) gave information about the two C-alpha-S rotational barriers, which are dominated by steric effects. Cryoscopy of [(RC)-C-1(R-2)SO(2)tBu]Li in THF at -108 degrees C revealed the existence of monomers and dimers. X-ray crystal structure analysis of the monomers and dimers of [(RC)-C-1(R-2)SO(2)tBu]Li center dot L-n (R-1 = Me, Et, tBuCH(2), PhCH2, tBu; R-2 = Ph, L = THF, 12-crown-4, PMDTA) and [(RC)-C-1(R-2)SO2Ph]Li center dot 2diglyme [R-1 = R-2 = Me, Et; R-1-R-2 = (CH2)(5)] showed them to be O-Li contact ion pairs (CIPs). The monomers and dimers have a C-alpha-S conformation in which the lone-pair orbital at the C-alpha atom bisects the O-S-O angle and a significantly shortened C -S bond. The C-alpha atom of [(RC)-C-1(R-2)SO2R3]center dot L-n (R-1 = Ph; R-3 = Ph, tBu) is planar, whereas the C-alpha atom of [(RC)-C-1(R-2)SO2R3]Li center dot I., (R-1 = R-2 = alkyl) is strongly pyramidalized in the case of R-3 = Ph and most likely planar for R-3 = tBu. Ab initio calculations on [MeC(Me)SO2R](-) gave a pyramidalized C-alpha atom for R = Me and a nearly planar one for R = CF3 and tBu. The [(RC)-C-1(R-2)SO(2)tBu]Li salts were characterized by H-1, C-13, and Li-6 NMR spectroscopy.H-1{H-1} and Li-6{H-1} NOE experiments are in accordance with the existence of O-Li CIPs. H-1 and C-13 NMR spectroscopy of [(RC)-C-1(R-2)SO(2)tBu]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 Li-7 NMR spectroscopy, the addition of HMPA to [MeC(Ph)SO(2)tBu]Li in [D8ITHF at low temperatures causes the formation of the separated ion pair [MeC(Ph)SO(2)tBu]Li(HMPA)(4).