Learning about Steric Effects in NHC Complexes from a 1D Silver Coordination Polymer with Fréchet Dendrons

The complex (NHC)­AgBr, which bears G1 poly­(benzyl ether) dendritic substituents in the NHC ligand, forms a 1D coordination polymer based on unusual zigzag −Ag–halide– chains. The asymmetric distribution of the volume buried by the NHC ligand in the Ag coordination sphere is important to explain the formation of this structure. A <i>V</i>_bur eccentricity parameter has been introduced and used in conjunction with the %<i>V</i>_bur descriptor to analyze the X-ray structures of 100 (NHC)­AgX complexes

Poly(benzyl ether) Dendrimers Functionalized at the Core with Palladium Bis(<i>N</i>‑Heterocyclic Carbene) Complexes as Catalysts for the Heck Coupling Reaction

Bis­(imidazolylidene)palladium complexes <b>9</b>–<b>12</b> containing a sterically hindered aryl group (mesityl or 2,6-diisopropylphenyl) and a poly­(benzyl ether) dendron as N-substituents of the NHC ligand are accessible up to the third generation by transmetalation of the corresponding silver complexes. Complexes <b>9</b>–<b>12</b> are soluble, active, and very stable catalysts under Heck reaction conditions. The NHC ligand appears to be stably coordinated to the Pd during catalysis. The catalytic activity increases with generation number, although irregularly. The palladium site is not significantly congested in the reaction solvent by the increasing size of the dendritic substituents, as corroborated by X-ray diffraction, fluorescence and DOSY-NMR spectroscopy, and MD simulation studies. This is a consequence of the conformational semiflexibility of the poly­(benzyl ether) dendrons and the benzylic link between these dendrons and the N-heterocyclic ligands