Fluorinated elements of Group 15 as pnictogen bond donor sites

The presence of fluorine atom(s) in a molecule makes the Ï\u83-hole potentials of surrounding atoms more positive and thus increases their tendencies to interact attractively with nucleophiles. This review shows that in the crystal structures of fluorinated derivatives of the Group 15 atoms, close contacts between Group 15 atoms and negative sites (e.g. lone pair possessing atoms and anions) are quite common. These close contacts are taken as indications of attractive interactions. The collection of single crystal X-ray structures analysed in this paper demonstrates that the ability of fluorinated atoms of Group 15 to work as electrophilic sites, namely to function as pnictogen bond donors, is fairly general. The directionalities and separations of these pninctogen bonds are convincing experimental evidences that linking a fluorine to a pnictogen atom increases its electrophilicity to the point that pnictogen bonding formation may become a determinant of the lattice structures in crystalline solids. Pnictogen bonding formation may become an heuristic principle for predicting some of the short contacts that are present in the crystal structures of compounds containing fluorinated atoms of Group 15, particularly when polyfluorinated. Pnictogen derivatives containing other moieties may also work as effective electrophilic sites and a convenient design of the used tectons may allow pnictogen bond to become a general and reliable tool in crystal engineering

Close contacts involving germanium and tin in crystal structures: experimental evidence of tetrel bonds

Modeling indicates the presence of a region of low electronic density (a σ-hole) on group 14 elements, and this offers an explanation for the ability of these elements to act as electrophilic sites and to form attractive interactions with nucleophiles. While many papers have described theoretical investigations of interactions involving carbon and silicon, such investigations of the heavier group 14 elements are relatively scarce. The purpose of this review is to rectify, to some extent, the current lack of experimental data on interactions formed by germanium and tin with nucleophiles. A survey of crystal structures in the Cambridge Structural Database is reported. This survey reveals that close contacts between Ge or Sn and lone-pair-possessing atoms are quite common, they can be either intra- or intermolecular contacts, and they are usually oriented along the extension of the covalent bond formed by the tetrel with the most electron-withdrawing substituent. Several examples are discussed in which germanium and tin atoms bear four carbon residues or in which halogen, oxygen, sulfur, or nitrogen substituents replace one, two, or three of those carbon residues. These close contacts are assumed to be the result of attractive interactions between the involved atoms and afford experimental evidence of the ability of germanium and tin to act as electrophilic sites, namely tetrel bond (TB) donors. This ability can govern the conformations and the packing of organic derivatives in the solid state. TBs can therefore be considered a promising and robust tool for crystal engineering

Extension of the Pd-catalyzed CN bond forming reaction to the synthesis of large polydentate ligands containing NH functions

The use of Pd(0) mediated CN coupling reaction for the synthesis of large polydentate ligands functionalized with NH groups is described. The protocol has been applied to the synthesis of polycarboxylic ligands and polypyridyl ligands, starting from common aryl halides containing a central phenyl or biphenyl core as electrophiles. Different aromatic amines or isonicotinamide have been used as nucleophiles. In all cases the ligands have been isolated in high yields and purity. The products have been characterized by means of FTIR, 1H NMR, 13C(1H) NMR, EI-MS or CI-MS and elemental analysis. The X-ray structure of N,N'-(biphenyl-4,4'-diyl)diisonicotinamide has also been solved