Dimethylpalladium complexes

Reetz et al. 16) were the first to recover and recycle a dendritic catalyst through a precipitation procedure. The dimethylpalladium complex of the phosphine-functionalized DAB-dendr-[N(CH2PPh2)2]i6 dendrimer (la) is an active catalyst for the Heck reaction of bromobenzene and styrene to give trara-stilbene (89% trans-stilbene and 11% 1,1-diphenylethylene, at a conversion of 85—90%, Scheme 8). 

Scheme 5.40 depicts the plausible mechanism of the isomerization of trans-dimethylpalladium complex with phosphine ligands to its cis isomer [205]. The three-coordinated dimethylpalladium complex, which is formed via dissociation of a phosphine ligand, reacts with the four-coordinated complex to cause intramolecular methyl ligand exchange. The reaction of trans and cis complexes affords two cis complexes as shown in the above scheme. This promoting effect of the cis complex in the isomerization of trans to cis complex gives autocatalytic type kinetics of the reaction. 

Scheme 1.44 Reductive elimination of ethane from dimethylpalladium complexes with diphosphine ligands 76a-d.

In the thermal decomposition of dimethylpalladium complex under CO, dimethyl diketone is produced together with acetonc. P The process of alkyl migration to coordinated CO in the reactions of cis- and trani-dialkylpalladium complexes has been established on the basis of the observation of the distribution of the products.P P P P ... 

Sources of catalytically active palladium(O) typically arise from ligand dissociation from coord-inatively more saturated Pd° complexes871-880 or from reduction of a Pd11 species.353,881 Another route to catalytically active (P—P)Pd fragments is the dissociation of the dinuclear complexes [(//-P—P)Pd]2.882 Complexes [(/r-dcpm)Pd]2 and [(/r-dtbpm)Pd]2 were obtained from the reductive elimination of ethane from dimethylpalladium(II) complexes (dippm = bis(diisopropylphosphino)methane dcpm = bis(dicyclohexylphosphino)methane dcpm = bis(di-t-butylphosphino)methane).883... 

There is continumg interest in the organometalhc chemistry of Pd. This oxidation state has often been invoked as an intermediate in the reactions of Pd species with reactive acyl or alkyl halides. Spectroscopic evidence has been obtained for this hypothesis. When phenacyl bromide reacts with dimethylpalladium(n) complexes, such as PdMe2(bpy), a complex can be isolated at 0 °C, which is shown, by H NMR and X-ray crystallography, to be PdBrMe2(CH2COAr)(bpy) (equation 2). The same complex reacts with Mel to form PdIMe3(bpy). The d Pd complexes are expected to exhibit... 

Dimethylpalladium(ll) complex with PEt2Ph ligand undergoes alkylation by MeLi or PhLi to afford palladate complexes which are characterized by NMR spectra of the solution. Detailed NMR studies of mixtures of the complex and MeLi or PhLi in various ratios revealed stepwise conversion of the neutral dimethyl complex into monoanionic palladate and then into homoleptic dianionic tetraorganopalladate complexes [38] (Scheme 5.6). 

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