Organometallic chemistry palladium complexes

Cavell KJ, McGuinness DS (2007) Palladium complexes with carbonyl, isocyanide and carbene ligands. In Crabtree RH, Mingos DMP, Canty AJ (eds) Comprehensive organometallic chemistry 111. Elsevier, Amsterdam... 

Dixon, K. R. Dixon, A. C. Palladium Complexes with Carbonyl, Isocyanide and Carbene Ligands, In Comprehensive Organometallic Chemistry II A review of the literature 1982-1994 Puddephatt, R. J. Ed., Elsevier, 1995, Vol. 9, p 193. 

In reactions requiring palladium 0), formation of the active complex may be achieved more conveniently by reduction of a palladium(ll) complex, for example, Pd 0Ac)2- Any phdsphine may then be used in the reaction, without the need to synthesize and isolate the corresponding palladium 0)-phosphine complex. Only 2-3 equivalents of phosphine may be needed, making the palladium(O) complex coordinatively unsaturated and therefore very reactive. The reduction of palladium li)to palladium(o) can be achieved with amines, phosphines, alkenes, and organometailics such as DIBAL-H, butyl lithium, or trialkyl aluminium. The mechanisms are worth giving as they illustrate the basic steps of organometallic chemistry. 

Fig. S. Diagrams of the halogenomethyl palladium complexes prepared by McCrindle el al. [Adapted with permission from the American Chemical Society, Elsevier Sequoia S. A., and the Royal Society of Chemistry from R. McCrindle, G. Ferguson, G. J. Arsenault, A. J. McAlees, B. L. Ruhl, and D. W. Sneddon, Organometallics 5,1171 (1986) R. McCrindle and D. W. Sneddon, J. Organomet. Chem. 282, 413 (1985) R. McCrindle, G. J. Arsenault, R. Farwaha, A. J. McAlees, and D. W. Sneddon, J. Chem. Soc., Dalton Trans., 761 (1989).]...

Another important piece of mechanistic evidence comes from the fact that acetaldehyde obtained from ethylene and deuterium-labeled water does not have any deuterium incorporation. In other words, all four hydrogen atoms of the ethylene molecule are retained. This means vinyl alcohol, which would certainly exchange the hydroxyl proton with deuterium, cannot be a free shortlived intermediate that tautomerizes to acetaldehyde. However, in spite of many elegant synthetic accomplishments in organometallic chemistry, realistic model complexes of palladium for 8.4 to 8.7 remain unknown. 

Four oxidation states of palladium are encountered in organometallic chemistry see Palladium Inorganic Coordination Chemistry) In order of importance, they are Pd , Pd , Pd, and Pd . With the reduction of palladium from Pd to Pd , the metal changes its reactivity from electrophile to nucleophile. However, unlike main group nucleophiles such as thiolates or cyanide, Pd complexes react with both alkyl halides and aryl or vinyl halides. Reactions of Pd complexes with these latter sp halides generate new Pd aryl or vinyl bonds through the process of oxidative addition. 

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