Synthesis of novel olefin complexes of palladium(0) bearing monodentate NHC, phosphine and isocyanide spectator ligands

We have synthesized and characterized seventeen new bis-NHC, mixed NHCâ\u80\u93phosphines or NHCâ\u80\u93isocyanides Pd(0) olefin complexes that can potentially act as catalysts. The complexes were characterized by standard spectroscopic methods and elemental analysis and in two cases by SC-XRD technique. We have analyzed with particular care the thermodynamic and kinetic conditions governing the one-pot synthesis of the mixed complexes. In this respect we tried to validate our results by a dedicated computational study on the mutual distribution of the isomers that could be potentially formed. However, the computational result is not clear-cut owing to the not significant value of the calculated Î\u94G0. Finally, in one case we have measured the rate of the exchange reaction between not particularly encumbered olefins

Interplay of hydrogen bonding and other molecular interactions in determining the crystal packing of a series of anti-[beta]-ketoarylhydrazones

Publisher's version/PDFThe crystal structures of six anti-[beta]-ketoarylhydrazones are reported: (a1) (E)-2-(4-cyanophenylhydrazono)-3- oxobutanenitrile; (a2) (E)-2-(4-methylphenylhydrazono)-3-oxobutanenitrile; (a3) (E)-2-(4-acetylphenylhydrazono)-3-oxobutanenitrile; (a4) (E)-2-(2-methoxyphenylhydrazono)-3-oxobutanenitrile; (a5) (E)-2-(2-acetylphenylhydrazono)-3-oxobutanenitrile; (a6) (E)-2-(2-nitrophenylhydrazono)-3-oxobutanenitrile. All compounds contain the [pi]-conjugated heterodienic group HN--N==C--C==O and could form, at least in principle, chains of intermolecular N--H...O hydrogen bonds assisted by resonance (RAHB-inter). Compounds (a1) and (a2) form this kind of hydrogen bond though with rather long N...O distances of 2.948 (3) and 2.980 (2) [Angstrom], and compound (a6) undergoes the same interaction but even more weakened [N...O 3.150 (1) [Angstrom]] by the intramolecular bifurcation of the hydrogen bond donated by the N--H group. The intrinsic weakness of the intermolecular RAHB makes possible the setting up of alternative packing arrangements that are controlled by an antiparallel dipole-dipole (DD) interaction between two C==O groups of the [beta]-ketohydrazone moiety [compounds (a4) and (a5)]. The critical factors that cause the switching between the different packings turn out to be the presence of hydrogen bonding accepting substituents on the phenyl and, most frequently, the intramolecular N--H...O bond with the O atom of the phenyl o-substituent. The crystal packing is widely determined by RAHB-inter (three cases) or DD (two cases) interactions. Only compound (a3) displays a different packing arrangement, where the DD interaction is complemented by a non-resonant hydrogen bond between a p-acetyl phenyl substituent and the hydrazone N--H group [N...O 2.907 (2) [Angstrom]]. Crystal densities range from 1.24 to 1.44 Mg m[superscript -3] and are shown to increase with the number of intermolecular hydrogen bonds and other non-van der Waals interactions