Palladium addition

Metal chemical shifts have not found extensive use in relation to structural problems in catalysis. This is partially due to the relatively poor sensitivity of many (but not all) spin 1=1/2 metals. The most interesting exception concerns Pt, which is 33.7% abundant and possesses a relatively large magnetic moment. Platinum chemistry often serves as a model for the catalytically more useful palladium. Additionally, Pt NMR, has been used in connection with the hydrosilyla-tion and hydroformylation reactions. In the former area, Roy and Taylor [82] have prepared the catalysts Pt(SiCl2Me)2(l,5-COD) and [Pt()i-Cl)(SiCl2Me)(q -l,5-COD)]2 and used Pt methods (plus Si and NMR) to characterize these and related compounds. These represent the first stable alkene platinum silyl complexes and their reactions are thought to support the often-cited Chalk-Harrod hydrosilylation mechanism. 

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

Fortunately, most of the palladium addition reactions with olefins can be carried out catalytically in the palladium compound so that large amounts of the expensive palladium compounds are not needed. As in the inorganic palladium salt additions, cupric chloride is a useful reoxidant. This, of course, limits the catalytic reaction to cases where olefin isomerization is not a problem. The cupric chloride is reduced to cuprous chloride during the reaction. As in the acetaldehyde synthesis, the reaction may be made catalytic in copper as well as palladium by adding oxygen and, in this case, hydrogen chloride also. 

Alloy additions that are effective in helping retain passivity in the presence of both low dissolved oxygen concentration and acid corrosion products help reduce or avoid crevice attack. Additions of molybdenum to 18-8 stainless steel (type 316) and palladium additions to titanium (see Fig. 25.2, Section 25.2) are in this category. 

No significant reports concerning the palladium-addition of aryl moieties to ketones have been found in the literature however, an interesting palladium-catalyzed asymmetric addition of arylboronic acids to N-benzylisatin substrates using novel enantiopure biphenyl i)N-ligands was reported by Qin and coworkers in 2009 [51]. Despite the synthesis of this new enantiopure tetra-orf/jo-substituted phosphinoimine ligand with a biphenyl backbone (see Scheme 7.32), the synthesis of 3-aryl-3-hydroxyoxindoles (widespread in natural products with important biologicrJ activities) was tJso successfully accomplished (Scheme 7.32). 

The standard red-ox potential of tellurium in alkali chloride melts is more positive than that of palladium. Addition of elemental tellurium to NaCl-CsCl-U02Cl2 melt at 550 °C resulted in a quite slow uranium reduction reaction. After 180 min the oxidation state of uranium decreased to 5.92 and the concentration of uranium in the melt from 0.85 to 0.79 wt%. The absorption spectra contained two well pronounced bands corresponding to the uranyl(V) complex, U02Cl4 . 

Ti-6 -4V-Pd is a grade that has palladium additions (about 0.2 wt% Pd) for enhanced corrosion resistance. Sumitomo Titanimn has produced this grade. 

The synthesis of the hydantoins 33 was realized by Beller s group in the context of their work devoted to the synthesis of amino acid derivatives by palladiumacid-promoted hydroxy-halogen exchange on the P-hydroxy-N-acyl derivative obtained from urea/aldehyde condensation, fohowed by oxidative palladium addition and CO insertion (Scheme 13.15) [42]. 

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