No abstract

<p>What happens when a C−H bond is forced to interact with unpaired pairs of electrons at a positively charged metal? Such interactions can be considered as “contra-electrostatic” H-bonds, which combine the familiar orbital interaction pattern characteristic for the covalent contribution to the conventional H-bonding with an unusual contra-electrostatic component. While electrostatics is strongly stabilizing component in the conventional C−H<b>•••</b>X bonds where X is an electronegative main group element, it is destabilizing in the C−H<b>•••</b>M contacts when M is Au(I), Ag(I), or Cu(I) of NHC−M−Cl systems. Such remarkable C−H<b>•••</b>M interaction became experimentally accessible within (α-ICyD^Me)MCl, NHC−Metal complexes embedded into cyclodextrins. Computational analysis of the model systems suggests that the overall interaction energies are relatively insensitive to moderate variations in the directionality of interaction between a C−H bond and the metal center, indicating stereoelectronic promiscuity of fully filled set of <i>d</i>-orbitals. A combination of experimental and computational data demonstrates that metal encapsulation inside the cyclodextrin cavity forces the C−H bond to point toward the metal, and reveals a still attractive “contra-electrostatic” H-bonding interaction.</p>

No abstract

Alternating benzene–heteroaryl oligomers possess fascinating optoelectronic properties and a wide range of applications. This article presents the facile synthesis of benzene–pyrrole oligomers with diverse functional groups and the elongated alternating heterocycle–benzene–pyrrole oligoaryls. The syntheses are based on a one‐pot, three‐step reaction of propargylic dithioacetals and imines. The subtle influence of functional groups, such as ether, ester, hydroxy, and dithiacetal groups on the peripheral benzene rings, on the reaction, has been explored and the reaction conditions were finely changed accordingly to achieve reasonable yields. The elongation could be accomplished by using a similar procedure. The fluorescent properties of original and elongated alternating benzene–pyrrole oligomers were determined. Theoretical calculations preliminarily reveal that the fluorescent intensity is closely related to the molecular geometry and to the HOMO/LUMO energy difference in the ground state.

<p><b>Abstract: </b>What happens when a C−H bond is forced to interact with unpaired pairs of electrons at a positively charged metal? Such interactions can be considered as “contra-electrostatic” H-bonds, which combine the familiar orbital interaction pattern characteristic for the covalent contribution to the conventional H-bonding with an unusual contra-electrostatic component. Whereas electrostatics is strongly stabilizing in the conventional C−H•••X bonds where X is an electronegative main group element, it is destabilizing in the C−H•••M contacts when M is Au(I), Ag(I), or Cu(I) of NHC−M−Cl systems. Such remarkable C−H•••M interaction became experimentally accessible within (a-ICyD^Me)MCl, NHC−Metal complexes embedded into cyclodextrins. Computational analysis of the model systems suggests that the overall interaction energies are relatively insensitive to moderate variations in the directionality of interaction between a C−H bond and the metal center, indicating stereoelectronic promiscuity of fully filled set of <i>d</i>-orbitals. A combination of experimental and computational data demonstrates that metal encapsulation inside the cyclodextrin cavity forces the C−H bond to point toward the metal, and reveals a still attractive “contra-electrostatic” H-bonding interaction.</p>