Palladium bromide

Example 24 Add. 1 mole of 3-(3,4-methylenedioxyphenyl) propylene,. 25 mole of methyl nitrite,. 008 mole palladium bromide as a catalyst,. 5L of methanol and 36g of water to a flask. Stir magnetically for 2 hoursat 25C. Yield of 3,4-methylenedioxyphenylacetone (also known as 3,4-... 

Tire early-late transition metal complex of Raymond et al. is interesting in that it requires both metal atoms to form the basic C3 structure (ideally D i, may form). Titanium complexation to three catechol units leads to a tridentate ligand, and, only when palladium bromide is added, trans coordination to palladium gives the agglomerate 31 [78]. 

Abstraction of chloride from a vinylpalladium complex by silver acetate has been reported,45 as well as halide abstraction by silver triflate from arylpalladium halides.46 More interestingly in the context of creating C-C bonds, silver perchlorate was able to promote the reaction of (r -aryl)palladium bromide with dienes. Silver-promoted bromide abstraction led to the formation of (r 1-r 2-enyl)palladium complexes, which evolved further through the regioselective formation of a C-C bond between the aryl group and the former diene. Reactions with nonconjugated dienes suggested that the reaction proceeds via carbometallation of the less crowded double bond. Isomerization and (3 elimination led to a (ri3-allyl)palladium complex (Scheme 10.26).47... 

Special attention should be paid to Maitlis s study of the 7r-cyclopenta-dienyl ligand transfer from iron to other metals in reactions of [(w-C5H5)Fe (CO)2]2 and (7r-C5H5)Fe(CO)2X with various compounds. In 1964 Maitlis, Efraty, and Games found 179) that (7r-C5H5)Fe(CO)2Br or [(w-C5H5)Fe (CO)2]2 react in boiling benzene with (tetraphenylcyclobutadiene) palladium bromide ... 

Later, the structure of the trimethylarsine-palladium bromide compound, [ (CH3)3As 2(PdBr2)2], was determined by x-ray crystal analysis (Mann and Wells, 1938) and found to possess the trans symmetric structure, XLIIIB, with a planar molecule 40), It should be added that each of the many bridged compounds prepared in these investigations appeared to be entirely homogeneous in the crystalline state. 

Catalyst (.008) mole of a palladium bromide Precursor 3-(4-methoxyphenyl)-propylene... 

The sole difference in the safrole conversion reaction is that in this case, palladium bromide is used instead of the palladium chloride used to convert allylbenzene. Since palladium bromide has a higher molecular weight than palladium chloride, the amount of palladium salt used in this case is increased by a factor of 1.5. 

Palladium chloride is prepared by treating Pd metal with CI2 at elevated temperatures. It exists as an essentially hnear doubly Cl-bridged polymer l.t i Palladium bromide is prepared from Pd and Br2 in the presence of nitric acid, while Pdl2 is normally prepared by treatment of PdCl2 with iodide ions. ... 

The proton NMR spectra of some of these complexes have been determined. The spectrum of cyclobutadieneiron tricarbonyl (XVIII) shows a singlet at 6.09r and that of benzocyclobutadieneiron tricarbonyl (XIX) a singlet at 5.98r due to the cyclobutadiene protons, as well as a multiplet due to the aromatic protons at 3.05r (3S). The NMR spectra of monosubstituted cyclobutadieneiron tricarbonyls (see Appendix) show the equivalence of the two cyclobutadiene ring protons adjacent to the substituent. This implies that the four-membered ring must be square (39a). Tetramethylcyclo-butadienenickel chloride in water shows only a single resonance due to the 12 equivalent methyl protons (32). The spectra of the tetraphenylcyclo-butadiene-metal complexes are those due to phenyl protons and are usually complex. In the (cyclopentadienyl)(tetraphenylcyclobutadiene)nickel and -palladium bromides (XLIV), however, sharp single phenyl proton resonances are obtained at 2.39r (65). The reason for the apparent equivalence of all the phenyl protons in (XLIV) is not clear. 

This reaction has also been carried out on the (cyclopentadienyl)(tetra-phenylcyclobutadiene)nickel and palladium bromides (XLIV, M = Ni, Pd) to give the (cyclopentadienyl)(l- xo-alkoxy-l,2,3,4-tetraphenylcyclobu-tenyl) complexes of palladium (LXXXV M = Pd, R=H, Me, Et) and nickel (LXXXV M = Ni, R = Me) (65). 

While sodium cyclopentadienide attacks tetramethylcyclobutadiene-nickel chloride both at carbon and nickel (Section VI, F), the discovery of a novel cyclopentadienylation reaction which is in effect a ligand-transfer reaction involving attack at the metal only has allowed other types of cyclobutadiene complexes to be prepared. Thus on reaction of tetra-phenylcyclobutadienenickel and -palladium bromides (LXXXVI) with cyclopentadienyliron dicarbonyl bromide, the paramagnetic (cyclopentadi-enyl)(tetraphenylcyclobutadiene)nickel and palladium tetrabromoferrates (LXXXVII M=Ni, Pd) are obtained 64, <55). 

Dimethyl-3-hexyne-2,5-diol - Palladium Bromide 4- Dimethylamino-1,4,4a,5,5a,6,11,12a-... 

Axially chiral allene can be racemized by addition-ehmination of AB, opposite to the other process above mentioned in this section (Schemes 5.28-5.41). Allenic alcohol was transformed to its butyrate in 83% yield with 89% ee by the combined system of NHC-palladium bromide complex together with hpase (Scheme 5.42) [115]. Although allenic esters are also racemized by this palladium complex, the half-life time of racemization is about fivefold longer than that of allenic alcohol. In the case of PdBr2(CH3CN)2, instead of NHC complex, the selectivity of the racemization was lost. The choice of palladium catalyst is important for this DKR system. 

Ill] and 1,5-cyclooctadiene palladium bromide react with [C Hg]Fe(CO)2Br to give compounds analogous to [VII]. The cyclopentadiene ring has also been transferred onto cobalt ... 

While such a process had initially been observed as an undesired side-reaction in transformations where copper salts were employed as re-oxidants [13], Chemler demonstrated that various aminohalogenation reactions proceed in THF or acetonitrile in the presence of potassium carbonate as base [14]. These reactions employ palladium trifluoroacetate or palladium dibromide as catalyst source and require a moderate excess of the copper oxidant (3-4 equiv) giving moderate to excellent yields. However, they usually suffer from rather low selectivity, either in the initial aminopalladation or via subsequent rearrangement pathways to provide mixtures of pyrrolidines and piperazines (Scheme 4.2, Eq. (4.3)). A stoichiometric control reaction in the presence of palladium bromide led only to the Wacker cydization together with an alkene isomerization product, suggesting that the presence of copper(II) salts is crucial for the overall process. The exact role of the copper(II) salts has not yet been darified and palladium intermediates of different oxidation states may be involved in the final stage of carbon-halogen bond formation. 

In 1991, a new C-N-C bond formation reaction using a nitrogenation-transmetalation process was described. Ketones and aryl or vinyl halides couple to give divinyl or arylvinyl amines in the presence of the titanium isocyanate complex [3THF MgaClaO TiNCO] and a palladium catalyst, via transmetallation of the titano imine complex with aryl or vinyl palladium bromide. Moderate to good yields of the desired products were observed (Scheme 2.176). 

Excellent examples of metal exchange reactions are provided by complexes of tetraphenylcyclobutadiene. When either iron pentacarbonyl or nickel carbonyl is reacted with tetraphenylcyclobutadiene palladium bromide, the corresponding metal is exchanged with the release of palladium(O) metal. The reaction proceeds only in aromatic solvents and seems to be generally applicable to a variety of transition metal carbonyls. As illustrated in Fig. 6-8, the first step is proposed to involve the formation of uncomplexed tetraphenylcyclobutadiene, a mixed metal halide carbonyl, carbon monoxide. 

This first plan for a decarboxylative cross-coupling carried with it certain weaknesses for potential industrial applications. It was to be expected that the salt metathesis between alkali metal carboxylates and late transition metal halides would be thermodynamically disfavored. We expected the formation of a palladium benzoate complex i from palladium bromide complexes c and potassium benzoate (g) to proceed well only in the presence of a stoichiometric quantity of silver to capture bromide ions [27]. However, we did not like the idea of using stoichiometric quantities of silver salts or of expensive aiyl triflates in the place of aryl halides. Finally, the published substrate scope of the oxidative Heck reactimi led to concerns that palladium catalysts mediate the decarboxylation rally of a narrow range of carboxylates, precluding use of this reaction as a general synthetic strategy. 

These concerns were supported by the first test reactirais in which we tried to couple benzoic acid with 4-bromoanisole in the presence of palladium complexes. We encountered great difficulties with generating the palladium benzoate from palladium bromide complexes in the absence of silver salts. Phosphine-stabilized palladium benzoates, especially aiylpalladium(ll) benzoates similar to i, did not extrude CO2 even at high temperatures. Only a small spectrum of palladium arenecarboxylates and phenylacetates was identified that lost CO2 upon heating. This is in agreement with a study of the protodecarboxylation activity of palladium published subsequently by Kozlowski [28]. 

Alternate Names palladium bromide palladium dibromide. Physical Data mp 717 2 °C X-ray structure. ... 

Rearrangements. Aryl-substituted methylenecyclopropanes undergo palladium-catalyzed ring expansion to afford cyclobutenes in moderate to good yields (eq 10) via the intermediacy of a palladium(II) carbenoid. Palladium bromide is either used directly or presumed to be formed in situ from Pd(OAc)2 and CuBr2. 

Palladium bromide is also an efficient Pd(0) catalyst precursor for the aminocarbonylation of benzyl chlorides (eq 46), car-bonylative Heck reaction of aryl bromides with vinyl ethers (eq 47), and carbonylation of halogenoalkynes (eq 48). ... 

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