Nickel complexes redistribution reactions

Recent Developments in Theoretical Organometallic Chemistry. 15, I Redistribution Equilibria of Organometallic Compounds, 6, 171 Redistribution Reactions of Transition Metal Organometallic Complexes, 23, 9S Redistribution Reactions on Silicon Catalyzed by Transition Metal Complexes, 19, 213 Remarkable Features of (7] -Conjugated Diene) zirconocene and -hafnocene Complexes, 24, I Selectivity Control in Nickel-Catalyzed Olefln Oligomerization, 17, lOS Silyl. Germyl, and Stannyl Derivatives of Azenes. N H Part I. Derivatives of Diazene, N,H2, 23, 131... 

While cationic catalysts 16 are an effective and important class of catalysts, their electrophilicity still hampers their ability to tolerate polar functions. The less electrophilic neutral 17-19 and zwitterionic 20 nickel catalysts have been examined in an effort to enhance compatibility with polar monomers and co-monomers. Again, bulky ligands are necessary not only to promote olefin insertion, but also to discourage ligand-redistribution reactions resulting in deactivated bis-ligand complexes and decomposition products. For a typical neutral Ni(ii) system, such as 19, Brookhart has shown that the mechanism involves (i) associative displacement of the PR3 ligand by ethylene to... 

Other kinetic studies concerned with square-planar nickel(ii) complexes include those of [Ni(trigly)] with Qfanide, redistribution reactions involving pairs of bis-bidentate nickel(n) complexes, and square-planar tetrahedral interconversions of [Ni(tertiary phosphine)2X2] compounds. ... 

Numerous complexes of nickel(II) and nickel(O) catalyze the addition of the Si-H bond to olefins. Among such catalysts are nickel-phosphine complexes, e.g., Ni(PR3)2X2 (where X=C1, I, NO3 R=alkyl and aryl), Ni(PPh3)4, and Ni-(CO)2(PPh3)2, as well as bidentate complexes of NiCl2-(chelate) and Ni(acac)2L (I phosphine), and Ni(cod)2(Pr3)2 [1-5]. A characteristic feature of nickel-phosphine-catalyzed olefin hydrosilylation is side reactions such as H/Cl, redistribution at silicon and the formation of substantial amounts of internal adducts in addition to terminal ones [69]. Phosphine complexes of nickel(O) and nickel(II) are used as catalysts in the hydrosilylation of olefins with functional groups, e.g., vinyl acetate, acrylonitrile [1-4], alkynes [70], and butadiynes [71]. 

A last case of sonication-sensitive catalytic reactions is the hydrogen-deuterium isotope exchange observed in carbohydrates in the presence of nickel or a nickel-aluminum alloy. A good selectivity is observed, probably due to the lower temperature allowed by sonication. However, a more complex origin can be responsible for these effects, since the sonicated alloy exhibits new features such as distinct catalytic centers, and elemental redistribution within the catalyst bulk, along with more classical consequences (surface cleaning, absence of surface area... 

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