Mercury palladium complexes

The mercuration of phosphonium derivatives has also been observed. The methylene group of the dimeric palladium complex 63 substituted by a carbonyl and a phosphonium functionality is readily mercurated upon reaction with Hg(OAc)2 to afford complex 64 (Equation (22)).7 Further studies demonstrated that the presence of a triphenylphosphonium group alone is sufficient to promote proton-mercury exchange. For example, the reaction of... 

A helical homobimetallic mercury(II) complex with a bridging bis(NHC) ligand serves as a starting point for a supramolecular assembly. Also tetrameric cyclic palladium(II) complexes have been obtained with bridging NHC-pyridine ligands. 

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... 

Amongst other ICC with five-link metal-cycles, we note o-indoline 877 (X = NTs) [160-163] and o-indophenol 877 (X = 0) [163,172,173] chelates, obtained in reaction (4.47). According to the expected results, palladium complexes of the type discussed are planar, while the ICC of zinc, mercury, and lead are tetrahedral [161,172,173],... 

Selenium analogs of the mercury and palladium complexes are known, but no simple selenide complexes seem to have been reported. 

Bildstein et al. have previously shown that Fc functionalised NHC (annulated and nonan-nulated) can be successfully employed to synthesise a broad range of transition metal complexes [166]. These include palladium, tungsten and mercury. Interestingly, two different species of mercury NHC complexes could be synthesised and structurally characterised (see Figure 4.49), with the dinuclear complex being the precursor for the mononuclear one. 

Conversion of norbornadiene to nortricyclenes can also be achieved with organomercurials. This reaction proceeds via transmetalation to form a c-bonded organopalladium system which inserts norbornadiene. Thus an enrfo-cw-addition is observed. Conversions of this type were observed in the phenylation of dichloro(t -norbornadiene)palladium either with diphenyl-mercury or, more conveniently, with sodium tetraphenylborate to give di-/r-chlorobis(2 5,6-t -c ffo-3-phenylbicyclo[2.2.1]hept-e /o-2-yl)palladium (30) via cis addition.By contrast, the analogous platinum complex did not give a phenylation product. The palladium complex 30 underwent reversible ring closure to a nortricyclenyl complex 31 with pyridine. ... 

Palladation of the t- butylimines of aromatic aldehydes (86) followed by insertion of acrylonitrile into the resulting complexes (87) yields intermediates of type (88), which on heating undergo electrocyclic ring-closure to isoquinolines (91). 2 Alternatively insertion of styrene into the palladium complexes followed by hydrolysis to the carboxaldehydes, and methylimine formation, yields intermediates (90), which on treatment with mercury (II) acetate are converted into N-methylisoquinolones (89). 103... 

Studies of Configuration.— The separation of diastereomeric bisphosphonium salts was monitored by n.m.r. N.m.r. was also able to detect <3% of a minor isomer of the diphosphine palladium complex (26). Mercury-199 n.m.r. spectra showed extra splitting due to bound diastereomeric phosphorus groups. The threo- and erythro- forms of the phosphine (27) gave well separated signals (8p—17 and —27). Diastereomeric anisochronocity of various -aminophos-phonates (28) has also been reported. ... 

The mechanism of 1 1 complex formation between palladium(II) and catechol and 4-methylcatechol has been studied in acidic media, and the rate of 1 1 (and 1 2) complex formation between silver(II) and several diols is an order of magnitude higher in basic solution than in acidic. The kinetics of formation and dissociation of the complex between cop-per(II) and cryptand (2,2,1) in aqueous DMSO have been measured and the dissociation rate constant, in particular, found to be strongly dependent upon water concentration. The kinetics of the formation of the zinc(II) and mercury(II) complexes of 2-methyl-2-(2-pyridyl)thiazolidine have been measured, as they have for the metal exchange reaction between Cu " and the nitrilotriacetate complexes of cobalt(II) and lead(II). Two pathways are observed for ligand transfer between Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) and their dithiocarbamate complexes in DMSO the first involves dissociation of the ligand from the complex followed by substitution at the metal ion, while the second involves direct electrophilic attack by the metal ion on the dithiocarbamate complex. As expected, the relative importance of the pathways depends on the stability of the complex and the lability and electrophilic character of the metal ion. 

Metal-activated alkene additions can be classified as stoichiometric or catalytic processes. Stoichiometric processes for THP synthesis typically involve the use of mercury(II) salts and to a lesser extent iodo and seleno reagents. The progress of intramolecular oxymercuration is determined by the stabiUty of the cationic intermediates. Product stereochemistry is under substrate control and usually leads to the thermodynamically more stable THP product. Catalytic variations generally involve palladium complexes [44], but other transition metals are becoming more common (e.g., Pt [45], Ag [46], Sn [47], Ce [48]). The oxidation state of Pd determines the catalyst reactivity. Palladium(O) complexes are nucleophilic and participate in tetrahydropyran synthesis through jt-allyl cation intermediates, whereas Pd(II) complexes possess electrophilic character and progress through a reversible t-complex. 

Several ylide-metal complexes have been reported recently. These complexes include palladium(ii), platinum(n), and mercury(n) complexes with keto-stabilized sulphonium ylides, with dimethylsulphonium methylide, and with dimethyl-sulphonium dicyanomethylide, as well as chromium, tungsten, molybdenum, and manganese complexes with dimethylsulphonium cyclopentadienylide. ... 

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