Abstract. The new N-heterocyclic carbene (NHC) precursors 4,5-dicyano-1,3-dimesityl-(9) and 4,5-dicyano-1,3-dineopentyl-2-(pentafluorophenyl)imidazoline (14) were synthesized. The structure of 9 could be determined by X-ray crystallography. With the 2-pentafluorophenyl-substituted imidazolines 9 and 14, the [AgCl (

Keywords:Copper / N ligands / Pi interactions / Self-assembly / Immobilization 2,11-Dialkylated 1,12-diazaperylenes (alkyl = Me, Et, iPr) dmedap, detdap and dipdap have been synthesized by reductive cyclization of 3,3Ј-dialkylated 1,1Ј-biisoquinolines 3a-c, resulting in the first copper(I) complexes of a "largesurface" ligand.

The new N-heterocyclic carbene (NHC) complex [PdCl 2 {(CN) 2 IMes}(PPh 3 )] (2) ({(CN) 2 IMes}: 4,5-dicyano-1,3dimesitylimidazol-2-ylidene) and the NHC palladacycle [PdCl(dmba){(CN) 2 IMes}] (3) (dmba: N,N-dimethylbenzylamine) have been synthesized by thermolysis of 4,5-dicyano-1,3-dimesityl-2-(pentafluorophenyl)imidazoline (1) in the presence of suitable palladium(II) precursors. The acyclic complex 2 was formed by ligand exchange using the mononuclear precursor [PdCl 2 (PPh 3 ) 2 ] and the palladacycle 3 was formed by cleavage of the dinuclear chloro-bridged precursor [Pd(μ-Cl)(dmba)] 2 . The new NHC precursor 1-benzyl-4,5dicyano-2-(pentafluorophenyl)-3-picolylimidazoline (5) was formed by condensation of pentafluorobenzaldehyde with Nbenzyl-NЈ-picolyldiaminomaleonitrile (4). The NHC palladacycle [PdCl 2 {(CN) 2 IBzPic}] (6) ({(CN) 2 IBzPic}: 1-benzyl-4,5dicyano-3-picolylimidazol-2-ylidene) was prepared by in situ [a] 2952 thermolysis of 5 in the presence of [PdCl 2 (PhCN) 2 ]. The three palladium(II) complexes were characterized by NMR and IR spectroscopy, mass spectrometry and elemental analysis. In addition, the molecular structures of 2 and 3 were determined by X-ray diffraction. The π-acidity of (CN) 2 IBzPic was compared with (CN) 2 IMes and perviously reported π-acidic imidazol-2-ylidenes by NBO analysis. The Mizoroki-Heck (MH) reactions of various aryl halides with n-butyl acrylate were performed in the presence of complexes 2, 3 and 6. The new precatalysts showed high activity in the MH reactions giving good-to-excellent product yields with 0.1 mol-% precatalyst. The nature of the catalytically active species of 2, 3 and 6 was investigated by poisoning experiments with mercury and transmission electron microscopy. It was found that palladium nanoparticles formed from the precatalysts were involved in the catalytic process.Scheme 2. Preparation of NHC palladium(II) complexes 2 and 3.

The PEPPSI (Pyridine Enhanced Precatalyst Preparation, Stabilization and Initiation) complexes 12-15 with the structure [PdCl 2 {(CN) 2 IMes}(3-R-py)] (12: R = H; 13: R = Cl; 14: R = Br; 15: R = CN) bearing the maleonitrile-based N-heterocyclic carbene (NHC) (CN) 2 IMes ({(CN) 2 IMes}: 4,5-dicyano-1,3-dimesitylimidazol-2-ylidene) were prepared. Solid state structures of 14 and 15 were obtained. Complexes 14 and 15 adopt a slightly distorted square-planar coordination geometry in the solid state with the substituted pyridine ligand trans to the NHC. Catalytic activities of precatalysts 12-15 were studied and subsequently compared to complexes

The phenylidenepyridine (ppy) palladacycles [PdCl(ppy)(IMes)] (4) [IMes = 1,3‐bis(mesityl)imidazol‐2‐ylidene] and [PdCl(ppy){(CN)2IMes}] (6) [(CN)2IMes = 4,5‐dicyano‐1,3‐bis(mesityl)imidazol‐2‐ylidene] were prepared by facile two step syntheses, starting with the reaction of palladium(II) chloride with 2‐phenylpyridine followed by subsequent addition of the NHC ligand to the precatalyst precursor [PdCl(ppy)]2. Suitable crystals for the X‐ray analysis of the complexes 4 and 6 were obtained. It was shown that 6 has a shorter NHC‐palladium bond than the IMes complex 4. The difference of the palladium carbene bond lengths based on the higher π‐acceptor strength of (CN)2IMes in comparison to IMes. Thus, (CN)2IMes should stabilize the catalytically active central palladium atom better than IMes. As a measure for the π‐acceptor strength of (CN)2IMes compared to IMes, the selone (CN)2IMes·Se (7) was prepared and characterized by 77Se‐NMR spectroscopy. The π‐acceptor strength of 7 was illuminated by the shift of its 77Se‐NMR signal. The 77Se‐NMR signal of 7 was shifted to much higher frequencies than the 77Se‐NMR signal of IMes·Se. Catalytic experiments using the Mizoroki‐Heck reaction of aryl chlorides with n‐butyl acrylate showed that 6 is the superior performer in comparison to 4. Using complex 6, an extensive substrate screening of 26 different aryl bromides with n‐butyl acrylate was performed. Complex 6 is a suitable precatalyst for para‐substituted aryl bromides. The catalytically active species was identified by mercury poisoning experiments to be palladium nanoparticles.