Theoretical investigation of Carbon-Sulfur triple bonds

AZUFRE

CARBON

CALCULOS AB INITIO

CALCULOS DE LA DENSIDAD

BIBLIOGRAFIA NACIONAL QUIMICA

2011

By means of first principle calculations we have investigated a set of molecules that are presumed to contain carbon–sulfur triple bonds, namely HCSOH, H3SCH, cis-FCSF, F3CCSF3, and F5SCSF3. For HCSOH, FCSF, and H3SCH we used the CCSD(T) methodology and the correlation-consistent basis sets. On the other hand, F3CCSF3 and F5SCSF3 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 kcalmol1), or a diabatic bond dissociation energy (DBDE) larger than the one found in SCO (212.0 kcal mol1), although the DBDE of FCSF comes quite close at 208.3 kcalmol1. The CS ABDEs of F3CCSF3, F5SCSF3, and H3SCH are comparable to that of a single CS bond. In contrast with the experimental results, F3CCSF3 and F5SCSF3 are predicted to be linear with C3v and Cs symmetry, respectively, at the B3LYP/6-311+GACHTUNGTRENUNG(3df,2p) level. MP2/6-311+GACHTUNGTRENUNG(2df,2p) calculations support the C3v symmetry for F3CCSF3, despite F5SCSF3 not having a perfect linear structure; the CSC angle is 174.68, which is nearly 208 larger than the experimental value. The analysis of the carbene structures of HCSOH and H3SCH revealed that they are not significant, because the triplet state is dissociative in these cases. However, for F3CCSF3 and F5SCSF3, the carbene triplet states lie 0.81 and 0.77 eV above the singlet state, respectively. In the same vein, our investigation supports the presence of a strong double bond for HCSOH. The conflicting evidence available for F3CCSF3 and F5SCSF3 makes it very difficult to determine the nature of the CS bonds. However, the bond dissociation energies and the singlet– triplet splittings clearly suggest that these compounds should be considered as masked sulfinylcarbenes. The analysis of the bond dissociation energies challenges the existence of a triple bond in these five molecules, but from a strictly thermodynamic standpoint, cis-FCSF is found to be the candidate most likely to exhibit triplebond character.

Chemistry European Journal v. 17, no. 6, 2011. -- p. 1979-1987

Wiley

2011

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http://dx.doi.org/10.1002/chem.201002840