Organometallic compounds palladium catalysis

Herrmann, W.A. (1996) Catal5dic carbon-carbon coupling by palladium complexes Heck reactions, in Applied Homogeneous Catalysis with Organometallic Compounds (eds B. Comils and W.A. Herrmann), Wiley-VCH Verlag GmbH, Weinheim, pp. 712-32. 

Notably, the catalyst system is currently used on multi-1,000 kg-scale. The efficiency and easy handling properties (stable to air and moisture) make this the first industrial palladium-catalyzed reductive carbonylation of aryl halides. At this point it is important to note that applied homogeneous catalysis benefits significantly from advancements in the area of organometallic chemistry. Hence, the mechanistic understanding of elementary steps and the synthesis of new organometallic compounds provide a valuable source for inspiration for new catalysts. 

Af-Heterocyclic carbenes and phosphine ligands can bind metal centers in a somewhat similar feshion via dative coordination using a lone pair of electrons. Therefore, phosphines are often considered to be the closest neighbors to NHCs in terms of organometallic chemistry. However, the properties of these two classes of compounds can be quite different, and can yield, for example, catalysts with quite different reactivity. The use of NHCs in olefin metathesis [25] and in palladium catalysis [26], for example, has allowed the preparation of highly active and stable species that are now at the forefront of their fields. Various studies have been conducted to explore the nature of bonding between NHCs and metal centers. Diez-Gonzalez and Nolan reviewed some aspects of NHC coordination to metal centers in 2007 [27]. 

In homogeneous catalysis telomerization is defined as the oligomerization of dienes with incorporation of a nucleophile. For example, two molecules of butadiene react with one nucleophile HY to form telomers. This reaction is catalyzed by various organometallic compounds of the transition metals, especially by palladium and nickel complexes. 

Many other types of organometallics which are not acylated directly acid chlorides and which do not undergo addition to ketones may still transmetallate into the acylpalladiumfll) complex. Simple alkyl organomercurials have been acylated in this fashion to give moderate to good yields of ketones. " Larock has studied the palladium-catalyzed acylation of vinylmercury(II) compounds with acyl halides (equation 104). The reaction was only modestly productive and could not compare to the yield provided by aluminum chloride catalysis. 

The C—I bond is very unstable and more reactive than C—Br, C—Cl and C—F bonds. Iodine is the most expensive of the common halogens and is much less frequently used in synthesis than bromine, chlorine or fluorine. Organometallic reactions proceed with iodinated aliphatic or aromatic compounds more easily than with the other halogens. Noble metal catalysis with palladium complexes is most effective with iodinated compounds. A useful synthetic procedure is the facile reduction of iodinated derivatives under mild conditions. Replacement of iodine by hydrogen at an sp carbon is an exothermic reaction with A// = -25 kJ mol . ... 

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