Oxo-palladium complexes

Ceric ammonium nitrate promoted oxidative addition of silyl enol ethers to 1,3-butadiene affords 1 1 mixtures of 4-(/J-oxoalkyl)-substituted 3-nitroxy-l-butene and l-nitroxy-2-butene27. Palladium(0)-catalyzed alkylation of the nitroxy isomeric mixture takes place through a common ij3 palladium complex which undergoes nucleophilic attack almost exclusively at the less substituted allylic carbon. Thus, oxidative addition of the silyl enol ether of 1-indanone to 1,3-butadiene followed by palladium-catalyzed substitution with sodium dimethyl malonate afforded 42% of a 19 1 mixture of methyl ( )-2-(methoxycarbonyl)-6-(l-oxo-2-indanyl)-4-hexenoate (5) and methyl 2-(methoxycarbonyl)-4-(l-oxo-2-indanyl)-3-vinylbutanoate (6), respectively (equation 12). 

The first palladium alkenyls, pzTpPd C,N-C(Cl) CHCMe2NMe2 (484)144 and the 3-oxo-hexenyl complex 493,160 were obtained systematically by halide displacement and dimer cleavage (Scheme 36). In common with alkyl and aryl systems (462—479, Section III.C.3), the pzTp ligand was in each case concluded to adopt a -coordination mode in solution, on the basis of (i) spectroscopic data, (ii) literature precedent, and (iii) the assumption that the Pd(II) centers in these complexes were too electron rich to permit coordination of the third pyrazole no solid-state data were reported. Both materials are fluxional in solution, and for 484 the slow-exchange limit was attained at —30 °C, with equilibration of the pyrazolyl environments becoming rapid at 79 °C, though the fast exchange limit... 

Other mild reagents have been introduced, among them BC13, BBr3,35 BF3 Et20,36 a rhenium(V)-oxo complex,37 and palladium complexes.38 Flydroxy-mercuration with mercury(II) acetate in aqueous tetrahydrofuran, followed... 

The present oxo-bridged and the similar chloro-bridged platinum complexes both undergo a single-step two-electron oxidation in 1,2-dichloroethane solution at potential values that are coincident with those of the corresponding palladium complexes (X = OH, E° (2-I-/4-I-) = -1-1.13 V X = Cl, ° (2-I-/4-I-) = -1-1.18 V) [164]. 

A novel synthesis of oxo-7r-allyl and rr-allyl palladium complexes using diazo compounds has been reported by Yoshimura and coworkers 298). These reactions proceed by carbene insertion in the Pd(II)—Cl bond ... 

The experimental results and the known facility of O-desilylation of silyl enol ethers, such as 3-acetoxy-2-trimethylsiloxypropenes, under the given reaction conditions led Trost ° to suggest the intermediacy of an oxatrimethylenemethanepalladium complex 4 addition to the alkene at the less-substituted terminal carbon atom of 4 followed by tautomerism and ring closure would give rise to the cyclopropane. Since the palladium complex that is prepared from tris(dibenzylideneacetone)palladium(0)-chloroform complex [Pd2(dba)j CHClj] and triphen-ylphosphane also catalyzes the Brook rearrangement of an a-silyl ketone to a silyl enol ether, (2-oxo-3-silylpropyl) acetates can also serve as precursors of intermediate palladium complexes 4, and the same cyclopropanation reactions as with 3-acetoxy-2-trimethylsiloxypropenes can be carried out. 

Based on their results with (2-oxoalkyl) carbonates, Murai et al. have proposed that an oxa( r-allyl)palladium complex 5 rather than an oxatrimethylenemethanepalladium complex such as 4 is involved in the C-C coupling reaction with the alkene. The decisive argument is provided by the observation of a successful reaction with ethyl (2-oxo-2-phenylethyl)carbonate. In this case, and in contrast to the 2-oxopropyl derivate, the intermediate oxa(7u-allyl)palladium complex 5 would be unable to form an oxatrimethylenemethane complex similar to 4 by elimination of ethanol. 

Pyrimidinones 53 (R1 = Ph, R2 = R3 = H R1 = R2 = H, R3 = Ph) exist in solution as mixtures of hydroxy and 3//-oxo tautomers with the latter predominating. The same tautomeric interconversion was observed in solutions of palladium complexes of these compounds (96MI385). The data on tautomerism of perimidinones 51 (X = O R = H, Me, Et, -Pr) in solution are contradictory suggesting the predominance of either oxo tautomers 51b (94HCA121) or enol tautomers 51a (88MRC191). Only oxo tautomer was observed for 51 (X = O R = Me) in the solid state (94HCA121). 

Other Reactions of Unsaturated Steroids.—A review on organopalladium intermediates includes several steroidal examples. A mechanistic study of the formation of the 7r-allyl palladium complex (65) from the corresponding 3-oxocholest-4-ene led to the conclusion that initial 7r-complexing was rate limiting. Reactions of a series of similar ir-allyl palladium complexes (66)—(68) with dialkyl malonate ion gave the 3-oxo-A -6/S-yl malonates (69)—(71) respec-... 

P2B02PtC4oH57, Platinum(II). (3-methoxy-3-oxo-KO-propyl-KC )bis(triethylphos-phine)-, tetraphenylborate(l-), 26 138 P2BPtC44Ht3, Platinum(ll), (q -cyclo-octene)bis(triethylphosphine)-, tetra-phenylborate( 1 —), 26 139 P2C4H 4, Phosphine, 12-ethanediylbis(di-methyl-, nickel complex, 28 101 P2C25H22. Phosphine, methylenebis(di-phenyl-, palladium complex, 28 340 ruthenium complex, 26 276,28 225 P2C26H20, Phosphine, ethynnediylbis(di-phenyl-, ruthenium complex, 26 277, 28 226... 

---