Metathesis with palladium compounds

Negishi E, Tan Z (2005) Diastereoselective, Enantioselective, and Regioselective Carbo-alumination Reactions Catalyzed by Zirconocene Derivatives. 8 139-176 Netherton M, Fu GC (2005)Palladium-catalyzed Cross-Coupling Reactions of Unactivated Alkyl Electrophiles with Organometallic Compounds. 14 85-108 NicolaouKC, KingNP, He Y (1998) Ring-Closing Metathesis in the Synthesis of EpothUones and Polyether Natural Products. 1 73-104 Nishiyama H (2004) Cyclopropanation with Ruthenium Catalysts. 11 81-92 Noels A, Demonceau A, Delaude L (2004) Ruthenium Promoted Catalysed Radical Processes toward Fine Chemistry. 11 155-171... 

The four most common methods for the synthesis of late transition metal enolates are oxidative addition to halocarbonyl compoxmds, ligand metathesis with main group enolates or silyl enol ethers, nucleophilic addition of anionic metal complexes to halocarbonyl electrophiles, and insertion of an a,3-imsaturated carbonyl compoimd into a metal hydride. Examples of these synthetic routes are shown in Equation 3.47-Equation 3.50. Equation 3.47 shows the synthesis of a palladium enolate complex by oxidative addition of ClCHjC(0)CHj to Pd(PPh3), Equation 3.48 shows the synthesis of a palladium enolate complex by the addition of a potassium enolate to an aryl Pd(II) halide complex, and Equation 3.49 shows the synthesis of the C-bound W(II) enolate complex in Figure 3.7 by the addition of Na[( n -C5R5)(CO)jW] to the a-halocarbonyl compound. Finally, Equation 3.50 shows the synthesis of a rhodium enolate complex by insertion of but-l-en-3-one into a rhodium hydride. This last route has also been used to prepare enolates as intermediates in reductive aldol processes. - ... 

PaDadium.— The complexes [59 X = acac, Cla (59)(dimer), R = Ph or p-tolyl] formed by reaction of a-butyne, arylmercury, and palladium dichloride (followed appropriately by metathesis with acac ) exhibit a huxional process which can be arrested on the n.m.r. time-scale at 273 K. N.m.r. results are consistent with alternating co-ordination of palladium between the two double bonds in the dihapto-cyclopentadienyl ring. At higher temperatures (343 K) irreversible conversion of (59 R = Ph) into (60) occurs. This was shown to proceed via the intermediacy of (for instance) (61). A rather similar type of compound to (59) has been shown to... 

Trost [10] discovered a palladium-catalyzed enyne metathesis during the course of his study on palladium-catalyzed enyne cyclization. Treatment of the 1,6-enyne 25 with palladacyclopentadiene (TCPT, 26a) in the presence of tri-o-tolyl-phophite and dimethyl acetylene dicarboxylate (DMAD) in dichloroethane at 60°C led to cycloadduct 27 and vinylcyclopentene 28 in 97% yield in a ratio of 1 to 1 (Eq. 10). The latter compound 28 is clearly the metathesis product. 

Trost and Tanoury found an interesting skeletal reorganization of enynes using a palladium catalyst.In this reaction, the second product is derived from a metathesis reaction (Equation (5)). It was speculated that the reaction would proceed by oxidative cyclization of enynes with the palladium complex followed by reductive elimination and then ring opening. To confirm this reaction mechanism, they obtained a compound having a cyclobutene ring, which was considered to be formed by the reductive elimination (Equation (6)). 

This volume provides the reader with the most important and exiting results pertaining the use of NHC complexes in transition-metal catalysis. Following an introductory chapter, which deals with the properties of NHC compounds and discusses some insightful examples, routes to NHC complexes will be described, a prerequisite for doing catalysis. Chapters on NHC complexes in oxidation chemistry and in metathesis reactions are accompanied by a chapter on palladium-catalyzed reactions and another on catalysis by other metals. Finally, this book would be incomplete without treating applications in asymmetric catalysis, which rounds out this volume. 

Metal-catalyzed reactions constitute the second major type of reactions in which organolead compounds act as major partners of the reacting systems. The study of these reactions has considerably increased since COMC (1995) review and they can be divided in two subtypes reactions in which the organolead reactant acts as a stoichiometric partner and reactions in which the organolead is only a catalytic species. In this section, only the reactions with stoichiometric organolead will be reviewed, and these reactions are catalyzed by copper, palladium or rhodium species. The second type is the metathesis reactions where the lead compound acts only as a promoter in a complex catalytic system and is reviewed in Section 9.09.4. 

Transition-metal catalyzed metathesis of carbon-halogen bonds with Si-Si bonds provides useful access to organosilicon compounds. Most of the reaction may involve initial oxidative addition of the carbon-halogen bond onto the transition-metal followed by activation of the Si-Si bond to give (organosilyl)(orga-no)palladium(II) complex, which undergoes reductive elimination of the carbon-silicon bond. 

First, coordinatively unsaturated active palladium catalyst, PdL2, is produced via dissociation of the ligands, which then reacts with acyl halide to give the acylpalladium intermediate. Since deinsertion of CO of the acylpalladium derivatives may occur simul-taneously, the next step, transmetallation (so-called metathesis), is the most crucial for the efficiency of the overall reaction. A variety of organometallic compounds, such as boron, aluminum, copper, zinc, mercury, silicon, tin, lead, zirconium, and bismuth, are used as the partner in this coupling reaction without loss of CO. In this section, the important features of the cross-coupling reactions of a variety of organometallic compounds with acyl halides and related electrophiles are discussed. 

In the last few years the design and use of various disilane compounds has gained importance because of the reactivity of the Si-Si bond and the large potential for organic synthesis involved with it. Many publications offer us numerous examples of possible reactions at the silicon-silicon bond such as addition reactions with C-C double bonds or C-C triple bonds [1, 2], addition reactions with C-element multiple bonds (e.g. aldehydes, quinones, isocyanides) [3-5] or metathesis [6, 7] and cross-metathesis [8]. In the most cases the existence of a catalyst (palladium, platinum or nickel complexes) for activation of the silicon-silicon a bond is indispensable for a successful transformation [9-11]. 

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