The synthesis and structural characterization of a series of palladium complexes bearing N-heterocyclic carbenes (NHC) as supporting ligands are described. The reaction of commercially available [Pd(allyl)Cl]2 and isolated or in situ generated NHC leads to monomeric palladium complexes where one NHC is bound to the metal center, as indicated by spectroscopic and single-crystal X-ray diffraction studies. The relative reactivity trend for these complexes as catalysts in aryl amination is discussed in terms of ligand steric properties, which vary as a function of imidazole-nitrogen substituents and perturbation resulting in modulation of ring planarity. The concept of buried volume is used to quantify the steric demand of each NHC in the corresponding complexes.

Mononuclear palladium-allyl complexes bearing one N-heterocyclic carbene (NHC) ligand have been synthesized. These complexes offer a straightforward entryway into a number of catalytic cycles by simple action of a base.

A number of palladium-N-heterocyclic carbene (NHC) complexes were found to be active catalysts for the arylation of ketones. A large number of substrates, both aryl halides and ketones, are compatible with the reaction conditions. The ketone arylation reactions are achieved with low catalyst loading in short reaction times using aryl chlorides and triflates as reactive partners. [reaction: see text]

Palladium-catalyzed coupling reactions of 6,6‘-dihydroxyboron-2,2‘-dimethoxy-1,1‘-binaphthyl 5g and chloroarenetricarbonylchromium complexes 6a−c afforded complexes 7a−c with the binaphthyl residue directly linked to the (η6-arene)tricarbonylchromium entity. Coupling reactions of 2,2‘-dimethoxy, 3,3‘-diodo, and 6,6‘-diodo-1,1‘-binaphthyl 3h and 5h with ethynylarenetricarbonylchromium derivatives 6d − f and ethynylferrocene 9 yielded binaphthyl compounds linked to arenetricarbonylchromium and ferrocenyl derivatives 8a−c, 11a−c, 10, and 12 through a triple bond. Condensation of 2,2‘-dimethylmethoxy, 3-formyl, 1,1‘-binaphthyl 2a with (η6-phenyl)methyltriphenylphosphonium tricarbonylchromium 13 and ferrocenylmethyltriphenylphosphonium 18 gave binaphthyl compounds linked to arenetricarbonylchromium and ferrocenyl derivatives 14 and 19, respectively, through a double bond. X-ray analyses of the dinuclear chromium complex 8a and of the mononuclear chromium complex 17-Z are described.

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53 refs.]. -(KISSLING, R. M.; VICIU, M. S.; GRASA, G. A.; GERMANEAU, R. F.; GUEVELI, T.; PASAREANU, M.-C.; NAVARRO-FERNANDEZ, O.; NOLAN, S. P.; ACS Symp. Ser. 856 (2003) 323-341; Dep. Chem., Univ. New Orleans, New Orleans, LA 70148, USA; Eng.) -Lindner 25-264