Synthesis and structure of N -acetyliminosulfane-stabilized carbone C(SPh 2 NC(O)Me) 2

N -acetyliminosulfane-stabilized carbone


Introduction
Many functional organic compounds that enrich our lives, such as pharmaceuticals, agrochemicals, and polymers, are synthesized by catalytic reactions. 1,2 herefore, new catalysts with higher activity and higher efficiency should be developed.The reactivity of a metal complex catalyst depends on the ligand bound to the central metal, thus, a new ligand can be expected to alter the reactivity of a catalyst using it. 2,3 8][9] Carbones consist of two strong electron-donating ligands (L) coordinated to a central zero-valent carbon atom, which maintains four valence electrons in -and -type lone pair (LP) orbitals.Therefore, they are frequently described as general-type carbon complexes (L→C←L).[22][23][24] Herein, we report the synthesis, crystal, and electronic structure of N-acetyliminosulfane-stabilized carbone 3, and compare 3 to previously reported Nmethyliminosulfane-stabilized carbones A.

Results and Discussion
In our previous study, the key intermediate 1 was synthesized from the reaction of fluorodiphenyl- 6 sulfanenitrile with -lithiated methyl diphenyl- 6 -sulfanenitrile. 12The reaction of 1 with two equivalents of acetic anhydride in THF at -20 °C afforded the corresponding monoprotonated salt 2 in 87% yield (Scheme 1).The desired carobone 3 was prepared in essentially quantitative yield by passing a methanolic solution of 2 through an ion-exchange resin column (IRA-410, OH -form).The formation of 2 and 3 was confirmed by 1 H and 13 C NMR spectroscopy and elemental analysis.The 1 H and 13 C NMR spectroscopy results revealed four equivalent phenyl, two equivalent acetyl groups, and a central carbon atom.The 13 C NMR signal for the central carbon atom of 3 ( = 29.6 ppm) was shifted to a higher field relative to that of A ( = 39.7 ppm). 12Scheme 1. Synthesis of 3.
To verify the carbone character, we calculated the first and second proton affinities 32,33 (PA(1) and PA(2)) of 3 and compared them with the theoretically predicted values for the PAs of carbones A-E (Table 2).As expected, the theoretically predicted PA(1) (271.3 kcal mol -1 ) of bis(acetyliminosulfane)carbon(0) 3 is smaller than that of bis(methyliminosulfane)carbone(0) A and is the smallest PA discussed in this study (Table 2).These results suggest that the N-acetylated iminosulfane ligand has reduced the electron density at the carbone center of 3. Therefore, the functionality of the central carbon can be easily controlled by introducing electron-donating or -withdrawing substituents to the nitrogen atom of the iminosulfane ligand.PA(1) is predominantly determined by the energy level of the highest occupied s orbital of neutral carbone 3, whereas PA(2) is predominantly determined by the highest occupied p orbital of monoprotonated 2.

Conclusions
In conclusion, we successfully prepared the N-acetyliminosulfane-stabilized carbone 3 by the deprotonation of the corresponding protonated salt 2 with Amberlite/OH -form.In addition, the molecular structures of 2 and 3 were determined using X-ray crystallographic analysis.Furthermore, DFT calculations for 3 revealed that the two LPs at the central carbon atom are efficiently stabilized by an n-σ* interaction with adjacent acetyliminosulfane ligands, and the PA value of 3 is the lowest value among A-E.These results suggested that the electronic properties of the central carbon in the carbones can be tuned by choosing appropriate substituents.

Figure 1 .
Figure 1.Molecular structures of A-E and 3.

Figure 2 .
Figure 2. Molecular structure of 2 and 3. Ellipsoids are shown at 50% probability.Hydrogen atoms (except for that on Ccenter) and ClO4 -anions are omitted for clarity.

Figure 3 .
Figure 3.The optimized structure of 3 (left, hydrogen atoms are omitted for clarity) and its HOMO (center) and HOMO-1 (right).

Table 2 .
Calculated energy levels of the HOMO, HOMO-1 and proton affinities (PAs) of 3