The SF₅‐Unit as Steric Protecting Group; Synthesis and Structure of F₅SCSF₃

Abstract

The following experiment provides a clear decision in favor of 5@' [Eqn. (c)]: if 4a generates the isotopomer 5 a a 0 loss of both OHo and O D o will be observed in MSMS-experiments; should 6a @' be generated, then (provided the isomers are separated by considerable barriers) elimination of OD' would occur exclusively. The assumption of a barrier preventing the rapid equilibration 5a" + 6 a @ is justified: ab initio MO calculations[41 (UHF 6-3 IG*//6-31G* + ZPVE) indicate that 5 @' is 37.3 kcal/ mol more stable than 6" but that the barrier against the conversion 6@'+5@' is 44.5 kcal/mol. m / zi "" m / z -Fig. I. CA and N R mass spectra (Xe/02) of H2SOP0 (precursor 4) and HDSO?' (precursor 4a). a) CA of H2S0y0. b) NR of H2SOY0. c) C A of HDSOFO. d) NR of HDSOYO. The spectra were recorded on VG-lnstruments mass spectrometers of types ZAB-2F (Utrecht), and ZAB-HF-3F (Berlin) under the conditions given in Refs. [2, 3bl.

Theoretical Investigation of Carbon–Sulfur Triple Bonds

“…Nevertheless, its nonlinear nature is an argument against such a type of bonding, because triple bonds often present a linear geometry, particularly for sp-hybridized carbon atoms. The 19 F NMR spectra of 1 at low temperature endorsed the notion that all the fluorine atoms bound to sulfur are equivalent, [3] as well as those bound to carbon. This result suggested a free rotation of the CF 3 groups, and an equilibration of eventual differ-A C H T U N G T R E N N U N G ences in the SF bond lengths.…”

“…This molecule was prepared by cleaving HF from CF 3 CH=SF 4 or CF 5 CH 2 =SF 5 . [2][3][4][5][6] Four years later, the same group showed that F 5 SCSF 3 (2) can be isolated. Soon after the synthesis of these two intriguing molecules, several experimental [3][4][5][6] and theoretical [7,8] investigations were carried out to understand the nature of the carbon-sulfur triple bond.…”

“…For HCSOH, FCSF, and H 3 SCH we used the CCSD(T) methodology and the correlation-consistent basis sets. On the other hand, F 3 CCSF 3 and F 5 SCSF 3 were studied at the B3LYP, M06-2X, MP2, and G3 levels of theory. We found that none of these molecules display a carbon-sulfur adiabatic bond dissociation energy (ABDE) as strong as diatomic CS (170.5 kcal mol À1 ), or a diabatic bond dissociation energy (DBDE) larger than the one found in SCO (212.0 kcal mol À1 ), although the DBDE of FCSF comes quite close at 208.3 kcal mol…”

“…[4,6,8] Therefore, it was postulated that the inclusion of correlation effects induces a bending of the structure of CF 3 CSF 3 . In the case of compound 2, the CS bond length is even shorter as compared with 1; it was reported to be 1.401(9) and 1.392 in the gas phase [5] and crystal structure, [3] respectively. The electron diffraction results [5] yielded an SCS angle equal to 1598, at variance with the crystal structure, which presented a linear SCS skeleton.…”

“…The electron diffraction results [5] yielded an SCS angle equal to 1598, at variance with the crystal structure, which presented a linear SCS skeleton. [3] For more than 20 years there have not been any reports on new compounds having a CS triple bond. This situation changed in 2009, when a landmark investigation by Schreiner et al [9] reported the preparation of hydroxysulfalkyne (HCSOH) through a photochemical [1,3] shift from thioform-A C H T U N G T R E N N U N G aldehyde S-oxide.…”