Tethering of Pentamethylcyclopentadienyl and N‑Heterocycle Stabilized Carbene Ligands by Intramolecular 1,4-Addition to a Polyfluorophenyl Substituent

On treatment with silver­(I) oxide the complex [Cp*RhCl₂(κC-MeNC₃H₂NCH₂C₆F₅)] undergoes 1,4-addition of rhodium and methylene to the polyfluoroaryl ring, which loses aromaticity, affording [(η⁵,κ²<i>C</i>-C₅Me₄CH₂C₆F₅CH₂NC₃H₂NMe)­RhCl]

Intramolecular Hydrogen Bonding in Substituted Aminoalcohols

The qualifying features of a hydrogen bond can be contentious, particularly where the hydrogen bond is due to a constrained intramolecular interaction. Indeed there is disagreement within the literature whether it is even possible for an intramolecular hydrogen bond to form between functional groups on adjacent carbon atoms. This work considers the nature of the intramolecular interaction between the OH (donor) and NH₂ (acceptor) groups of 2-aminoethanol, with varying substitution at the OH carbon. Gas-phase vibrational spectra of 1-amino-2-methyl-2-propanol (BMAE) and 1-amino-2,2-bis­(trifluoromethyl)-2-ethanol (BFMAE) were recorded using Fourier transform infrared spectroscopy and compared to literature spectra of 2-aminoethanol (AE). Based on the experimental OH-stretching frequencies, the strength of the intramolecular hydrogen bond appears to increase from AE < BMAE ≪ BFMAE. Non-covalent interaction analysis shows evidence of an intramolecular hydrogen bond in all three molecules, with the order of the strength of interaction matching that of experiment. The experimental OH-stretching vibrational frequencies were found to correlate well with the calculated kinetic energy density, suggesting that this approach can be used to estimate the strength of an intramolecular hydrogen bond

Arene-Perfluoroarene-Anion Stacking and Hydrogen Bonding Interactions in Imidazolium Salts for the Crystal Engineering of Polarity

The crystal structure of 1-(2,3,5,6-tetrafluoropyridyl)-3-benzylimidazolium bromide possesses C₆H₅···C₅F₄N···Br^– interactions that link the cations into chains, N­(C)­C–H···Br^– interactions that link the chains into sheets, and N₂C–H···Br^– interactions that link the sheets to one another. As a consequence of these, it is polar (<i>Pna</i>2₁). Density functional theory calculations indicate that the strength of the interaction between a cation and a bromide anion lies in the order N₂C–H···Br^– > N­(C)­C–H···Br^– > C₆H₅···C₅F₄N···Br^–. Prevention of the N₂C–H···Br^– interaction by substitution of the hydrogen atom with a methyl group leads to dimers linked by two C₆H₅···C₅F₄N···Br^– interactions. Prevention of the N­(C)­C–H···Br^– interaction by substitution of the hydrogen with a methyl group permits chains of cations, but because the N₂C–H···Br^– interactions link the chains there are no strong interactions between the sheets. Chains of cations linked by Ar···C₅F₄N···Br^– interactions also arise when the benzyl group is replaced by 3-phenylbenzyl and 2-naphthylmethyl groups. The former also contains N₂C–H···Br^– and N­(C)­C–H···Br^– interactions and is centrosymmetric. The latter does not contain N­(C)­C–H···Br^– interactions and is chiral and polar (<i>P</i>2₁). Exchanging the positions of the aryl and polyfluoroaryl groups results in a crystal structure with no π–π stacking between the aryl and polyfluoroaryl groups although N₂C–H···Br^– and N­(C)­C–H···Br^– interactions persist