The halogen bonded adduct between the commonly used constituents quinuclidine and iodobenzene is based on a single weak nitrogen–iodine contact, and the isolation of this adduct was initially unexpected. Iodobenzene does not contain any electron-withdrawing group and therefore represents an unconventional halogen bond donor. Based on excellent diffraction data of high resolution, an electron density study was successfully accomplished and confirmed one of the longest N···I molecular halogen bonds with a distance of 2.9301(4) Å. The topological analysis identified the XB as a directional but weak σ hole interaction and revealed secondary contacts between peripheral regions of opposite charge. These additional contacts and their competition with a nitrogen-based interaction were confirmed by NOESY experiments in solution. Integration enabled us to determine the relative NOE ratios and provided insight regarding the existing interactions.

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Since its introduction in 2004, Knochel's so called Turbo-Grignard reagents revolutionized the usage of Grignard reagents. Through the simple addition of LiCl to a magnesium alkyl an outstanding increase in reactivity can be achieved. Though the exact composition of the reactive species remained mysterious, the reactive mixture itself is readily used not only in synthesis but also found its way into more distant fields like material science. To unravel this mystery, we combined single-crystal X-ray diffraction with in-solution NMR-spectroscopy and closed our investigations with quantum chemical calculations. Using such a variety of methods, we have gained insight into and an explanation for the extraordinary reactivity of this extremely convenient reagent by determining the structure of the first bimetallic reactive species [t-Bu 2 Mg • LiCl • 4 thf] with two tert-butyl anions at the magnesium center and incorporated lithium chloride.

The title compound [(N,N-dimethylamino)methyl]ferrocene, [Fe(C5H5)(C8H12N)], (1), is an interesting starting material for the synthesis of planar chiral 1,2-disubstituted ferrocenes, as demonstrated by the preparation of (R p,R p)-bis{2-[(dimethylamino)methyl]ferrocenyl}dimethylsilane, [Fe2(C5H5)2(C18H18N2Si)], (2), from the lithiated derivative of 1. The configuration of the lithium compound is unchanged after the substitution reaction and the chirality is preserved in space group P212121. In both compounds, the Cp rings adopt eclipsed conformations. Hirshfeld surface analysis was used to investigate the intermolecular interactions, and showed that H...H (van der Waals) interactions dominate in both structures with contact percentages of 83.9 and 88.4% for 1 and 2, respectively.

Strong and weak halogen bonds (XBs) in discrete aggregates involving the same acceptor are addressed by experiments in solution and in the solid state. Unsubstituted and perfluorinated iodobenzenes act as halogen donors of tunable strength; in all cases, quinuclidine represents the acceptor. NMR titrations reliably identify the strong intermolecular interactions in solution, with experimental binding energies of approx. 7 kJ/mol. Interaction of the σ hole at the halogen donor iodine leads to a redshift in the symmetric C–I stretching vibration; this shift reflects the interaction energy in the halogen-bonded adducts and may be assessed by Raman spectroscopy in condensed phase even for weak XBs. An experimental picture of the electronic density for the XBs is achieved by high-resolution X-ray diffraction on suitable crystals. Quantum theory of atoms in molecules (QTAIM) analysis affords the electron densities and energy densities in the bond critical points of the halogen bonds and confirms stronger interaction for the shorter contacts. For the first time, the experimental electron density shows a significant effect on the atomic volumes and Bader charges of the quinuclidine N atoms, the halogen-bond acceptor: strong and weak XBs are reflected in the nature of their acceptor atom. Our experimental findings at the acceptor atom match the discussed effects of halogen bonding and thus the proposed concepts in XB activated organocatalysis.