Abstract
Carbon bonding is a weak interaction, particularly when a neutral molecule acts as an electron donor. Thus, there is an interesting question of how to enhance carbon bonding. In this paper, we found that the –OCH3 group at the exocyclic carbon of fulvene can form a moderate carbon bond with NH3 with an interaction energy of about −10 kJ/mol. The –OSiH3 group engages in a stronger tetrel bond than does the –OGeH3 group, while a reverse result is found for both –OSiF3 and –OGeF3 groups. The abnormal order in the former is mainly due to the stronger orbital interaction in the –OSiH3 complex, which has a larger deformation energy. The cyano groups adjoined to the fulvene ring not only cause a change in the interaction type, from vdW interactions in the unsubstituted system of –OCF3 to carbon bonding, but also greatly strengthen tetrel bonding. The formation of tetrel bonding has an enhancing effect on the aromaticity of the fulvene ring.
Highlights
Fulvenes serve as synthetic precursors to naturally occurring compounds [1,2], and as starting materials for the synthesis of novel substituted titanocenes, which are bio-organometallic anti-cancer drugs [3]
REVIEW 6-OTX3 -fulvene and NH3 was further determined by AIM analysis
The main conclusions are summarized as: (1) The interaction energy of 6-OCH3 -fulvene···NH3 was up to −10 kJ/mol, which was twice as high as that in HOCH3 ···NH3, carbon bonding is enhanced when –OCH3 combines with fulvene ring
Summary
Fulvenes serve as synthetic precursors to naturally occurring compounds [1,2], and as starting materials for the synthesis of novel substituted titanocenes, which are bio-organometallic anti-cancer drugs [3]. Mani and Arunan performed a theoretical study of carbon bonding in complexes of methanol and methyl fluoride, where a methyl group is adjoined with an electron-withdrawing group, and found that in some neutral bases the acidity of the carbon atom increases, and the interaction energy amounts to ~8 kJ/mol [28] The ubiquity of such carbon bond was further witnessed in the solid state by means of Cambridge Structural Database (CSD) and charge density analyses [29]. It has been demonstrated that the hydroxyl proton of 6-OH-fulvene is acidic, and that its acidity increases greatly when cyano groups adjoin to the fulvene ring [13] Inspired by these findings, in this study, the hydroxyl H atom of 6-OH-fulvene was changed to –CX3 (X = H and F), which was able to form a stronger carbon bond with NH3. We focused on the effect of both TX3 and the formation of tetrel bonds on the aromaticity of the fulvene ring
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