Palladium chloride dimer

Coupling of n- allylic)paUadium complexes with an alkenylzirconium(IV) complex l,4-< enes.2 A recent stereospecific synthesis of natural (20R)-cholestanone-3 (4) involves coupling of the alkenylzirconium complex 2 with the jr-(allylic)palladium chloride dimer (1) of a (Z)-17(2U)-pregnene. The major product is a 1,4-diene (3), formed by regioselective attack of 2 at C20, the less hindered terminus of the allylic unit, and with inversion at C20. Coupling of 2 with the 7i-(allylic)palladium chloride dimer of the (E)-isomer of 1 results in a 1,4-diene epimeric at C20 with 3. Hydrogenation of the diene completes the synthesis of the desired natural cholestanone-3 (4). 

Epimerization of frans-4(R)H,9a(R)H-4-phenyl-8-benzyloxymethyl-3,4,9,9a-tetrahydro-lH,6H-pyrido]2,l-c][l,4]oxazin-l-one to cis-4(R)H,9a (S)H derivative in 30% yield was achieved by treatment with KHMDS in THF at 78 °C, followed by the addition of HMPA and AcOH at same temperature and after 15 min stirring the reaction mixture was quenched with the saturated NH4C1 solution (08JOC6877). A solution of cis-4(R)H,9a (S)H- and frans-4(R)H,9a(R)H-4-phenyl-8-benzyloxymethyl-3,4,9,9fl-tetra-hydro-lH,6H-pyrido]2,l-c][l,4]oxazin-l-ones in DMF containing HCO2H and NEt3 was added to a solution of allyl palladium chloride dimer and 2-di-ferf-butylphosphino-2 -methylbiphenyl in DMF at 10 °C for 6 h and room temperature for 16 h under nitrogen afforded cis-4(R)H,9a(S)H-and frans-4H,9aH-(4R,9aR)-4-methyleneperhydropyrido]2,l-c][l,4]oxa-zin-l-one, respectively. 

Bis(allyl)Pd and -Pt compounds are also made by treatment of PdClj and PtClj with RMgX see Table 4. Mixed bis(allyl)Pd complexes can be obtained when an allylic RMgX reagent or allyltin reagent is slowly added at — 30°C to an ether dioxane solution of ( t-allyl)palladium chloride dimer . Removal of pentane under vacuum affords the products as light golden-yellow crystalline solids in 80% yield. 

Similarly, Pd atoms with benzyl chloride yield a n-benzyl palladium chloride dimer which, although isolable, is reactive ... 

Allyl-palladium chloride dimer, 8.0 mg, 0.0219 mmols, 0.2mol%... 

A second Schlenk tube containing allyl-palladium chloride dimer (8.0 mg, 0.0219 mmols, 0.2mol%), l-chloro-3-fluorobenzene (1.71 mL, 1.43 g, 10.93 mmols) and a magnetic stirring bar was then placed under an inert atmosphere before the addition of dry toluene (15 mL). 

A typical reaction involving nickel(O) treats an allylic halide such as 3-chloro-2-methyl-l-propene with Ni(CO)4 to form 439,288 a nickel dimer analogous to the palladium chloride dimer discussed in the previous section. This complex reacts with an alkene to form a new complex (440), and subsequent reaction with a variety of electrophilic reagents removes nickel. In this example, the chlorine was converted to an acetate ligand (in 441) and reacted with methanolic carbon monoxide to give the ester (442).288... 

CgoH4oBr2Mo204, Di-/u bromo-bis(ir-tetraphenylcyclobutadiene) tetracar-bonyldimolybdenumd), 34B, 479 39B, 649 CgoH5oCl202Pd2, endo-1-Ethoxy-1,2,3,4-tetraphenylcyclobutenyl palladium chloride dimer, 30B, 326... 

Palladium chloride dimerizes ethylene at 20-70°C and 1—40 atm to yield butenes vvith 90% selectivity [245]. It has been suggested that this compound initiates the dimerization in the presence of hydrogen chloride by a mechanism analogous to that of Friedel-Crafts catalysis ... 

The allylation of cyclic acetates such as cyclopentenyl or cyclo-hexenyl and cycloheptenyl derivatives also has been widely studied. For exart ile, the allyl palladium chloride dimer (1) is a useful catalyst precursor in the kinetic resolution of 2-cyclohexenyl acetate using Trost s chiral ligands pockets in conjunction to the planar chirality of ferrocene (eq 46). 1 The conversion was stopped at 54%, which allowed high enantiomeric excess for both the alkylated derivative and the chiral allylic acetate. 

Steroidal 7t-allyl complexes can be oxidatively cleaved to allyl alcohols with high stereoselectivity (Jones and Knox, 1975b). For example, the n-allyl palladium chloride dimer, XIV, derived from cholest-4-ene, undergoes bridge cleavage by pyridine and then oxidation by w-chloroperbenzoic acid to give XVI as the sole product. Similar reaction of the isomeric Jt-allyl... 

Other allyl complexes, e.g. the 7r-allyl palladium chloride dimer show the A4X spectra only in the presence of ligands such as R3P, R3AS or dimethylsidphoxide. In this case it is concluded that the equilibration of the terminal hydrogens in the n.m.r. experiment is due to rapid exchange processes, e.g. 

Fig. 12. Some bridge cleavage reactions of w-enyl palladium chloride dimers. The acetylacetonate anion is represented by acac ...

The 7t-enyl palladium chloride dimers are readily hydrolysed at room temperature [62,10]. 

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