Volume 21, Issue 6 p. 540-545
Article

Blue-Shift Hydrogen Bonds in Silyltriptycene Derivatives: Antibonding σ* Orbitals of the Si−C Bond as Effective Acceptors of Electron Density

Dr. Adam Mames

Dr. Adam Mames

Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

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Dariusz Gołowicz

Dariusz Gołowicz

Centre of New Technologies, University of Warsaw, Banacha 2 C, 02-097 Warsaw, Poland

Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

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Dr. Mariusz Pietrzak

Dr. Mariusz Pietrzak

Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

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Dr. Krzysztof Kazimierczuk

Dr. Krzysztof Kazimierczuk

Centre of New Technologies, University of Warsaw, Banacha 2 C, 02-097 Warsaw, Poland

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Prof. Sławomir Szymański

Prof. Sławomir Szymański

Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

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Dr. Tomasz Ratajczyk

Corresponding Author

Dr. Tomasz Ratajczyk

Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland

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First published: 17 January 2020
Citations: 1

Graphical Abstract

Just looking? In a sterically congested triptycene derivative, there is a strong noncovalent interaction between the chloride atom at the peri position and the anti located Si−C bond from the −SiH2PhOMe group in position 9. For each of the syn oriented Si−H groupings, this interaction appears as a blue-shift hydrogen bond – BSHB. In many cases of BSHBs involving connections −SiH and −CH, the hydrogen atoms in the latter appear to be only passive witnesses of the interaction.

Abstract

Triptycene derivatives are widely utilized in different fields of chemistry and materials sciences. Their physicochemical properties, often of pivotal importance for the rational design of triptycene-based functional materials, are influenced by noncovalent interactions between substituents mounted on the triptycene skeleton. Herein, a unique interaction between electron-rich substituents in the peri position and the silyl group located on the bridgehead sp3-carbon is discussed on the example of 1,4-dichloro-9-(p-methoxyphenyl)-silyltriptycene (TRPCl) which exists in solution in the form of two rotamers differing by dispositions, syn or anti, of the Si−CPh (the CPh atom is from the p-methoxyphenyl group) bond against the peri-Cl atom. For the first time, substantial differences between the Si−CPh bonds in these two dispositions are identified, based on indirect experimental and direct theoretical evidence. For these two orientations, the experimental 1J(Si,CPh) values differ by as much as 10 percent. The differences are explained in terms of effective electron density transfer from the peri-Cl atom to the antibonding σ* orbitals of the Si−X bonds (X=H, CPh) oriented anti to that atom. The electronic effects are revealed by an NBO analysis. Connections of these observations with the notion of blue-shifting hydrogen bonds are discussed.