Cross-couplings and related reactions are a class of highly efficient synthetic protocols that are generally promoted by molecular Pd species as catalysts. However, catalysts based on more or less highly dispersed Pd metal have been also employed for this purpose, and their use, which was largely limited to the Heck reaction until the turn of the century, has been extended in recent years to most reactions of this class. This review provides a critical overview on these recent applications of Pd metal catalysts. Particular attention is devoted to the discussion of the mechanistic pathways that have been proposed to explain the catalytic role of Pd metal. Furthermore, the most outstanding Pd metal based catalytic systems that have emerged are illustrated, together with the development of novel approaches to boost the reactivity of Pd metal. A section summarizing the current industrial applications of Pd metal catalyzed reactions of this kind concludes the review.

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zoyl)methane (0.400 g, 0.89 mmol, 3.0 equiv.), 50 % (42 M) sodium hydroxide solution in water (40 mL, 1.68 mmol, 5.5 equiv.), and ethanol (40 mL). To another 50 mL Erlenmeyer flask was added europium(III) chloride hexahydrate (0.110 g, 0.3 mmol, 1 equiv.) and ethanol (10 mL). Both solutions were heated to 70 C while stirring. The ligand solution was added dropwise to the europium solution. Upon addition of the final third of the solution, a precipitate formed. The resulting solution was cooled to room temperature, filtered, and the solid was washed with water. The resulting complex [Eu(t-t) 3´x H 2 O] was isolated (0.260 g, 0.17 mmol, 56 % yield) and added to toluene (25 mL) and 1,10-phenanthroline (0.033 g, 0.19 mmol) and heated to 100 C for 30 min. The toluene was removed completely and the remaining solid was triturated with cold ethanol to remove the excess 1,10-phenanthroline giving 0.224 mg (0.134 mmol) of product (44 % yield relative to europium). Analysis: calculated (C 105 H 137 N 2 O 6 Eu): C, 75.28; H, 8.24; N, 1.67. Found C, 75.59; H, 8.15 One of the main targets of modern scientific research is to improve our skills in the controlled manipulation of matter at the nanoscopic level (ªnanotechnologyº).[1] Advances in this field may have tremendous implication for technological applications spanning from catalysis to information technology, from electronics to material science. Among the different materials which display peculiar properties once they are reduced to a nanometric size, metals represent one of the best known examples. [2,3] In fact, the physical and chemical properties of nanosized metals may significantly differ from those of the corresponding bulk metal. This is the consequence of alterations in the electronic band structure of the metal particle due to its small size, as well as of the presence of a high fraction of coordinately and electronically unsaturated atoms at the surface of the metal nanoparticles. Such peculiarities have important implications both for catalysis and material science; consequently, a great deal of scientific work is currently carried out by numerous research groups aimed at the development of synthetic methods for the preparation of metal nanoparticles in the size range 1±10 nm (ªmetal nanoclustersº).[2±4] Generally, a bottom±up approach has to be used; that is, metal nanoclusters are grown from metal atom precursors in the presence of a stabilizer able to interact with the nanocluster surface, thus preventing agglomeration and controlling its growth to a definite, possibly predetermined size. A variety of methods for the generation of the metal atom precursors have been proposed in the literature over the years, as well as a variety of stabilizers such as solvent molecules, ion pairs, surfactants, ligand molecules, and polymers.[2±6] The latter range from conventional linear macromolecules to systems with complicated architectures, such as block copolymer micelles [5] or dendrimers, [6] where the metal atom precursors are ªphysically confinedº within nanomet...

Dinuclear N-heterocyclic dicarbene gold(I) complexes of general formula [Au(2)(RIm-Y-ImR)(2)](PF(6))(2) (R = Me, Cy; Y = (CH(2))(1-4), o-xylylene, m-xylylene) have been synthesized and screened for their luminescence properties. All the complexes are weakly emissive in solution whereas in the solid state some of them show significant luminescence intensities. In particular, crystals or powders of the complex with R = Me, Y = (CH(2))(3) exhibit an intense blue emission (λ(max) = 450 nm) with a high quantum yield (Φ(em) = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au···Au distance (3.272 Ǻ). Time dependent density functional theory (TDDFT) calculations have been used to calculate the UV/vis properties of the ground state as well as of the first excited state of the complex, the latter featuring a significantly shorter Au···Au distance.