Nickel triade

Synthesis of electron-rich nickel triad complexes. E. Uhlig and D. Walther, Coord. Chem. Rev., 1980,33,3-53 (182). 

The optical spectra of the nickel-triad metals have been reinvestigated (111) in Ar, Kr, and Xe matrices, and, although the data for Ni and Pt atoms correlated well both with previous studies and with the... 

The metal-atom reactions of Cu (98), Ag (134), and Au (135) with O provided interesting results, especially when these were compared with the results from the nickel triad (137). As shown by standard matrix-techniques, Ag forms two O2 complexes that are best formulated as Ag 02 and Ag+Oj, based on the absence of visible absorptions and the similarity of the IR spectra to those of Cs" 02 and Cs Oj (3a,b). The UV absorptions for Ag(02) and AgiOJ, at 275 and 290 nm, respectively, could be associated with the O2 and O4 anions. The shifts in the IR spectra on going from Ag(02) to Ag(04) also argue against an (02)Ag(02) formulation for the latter complex, being in the opposite sense to those observed for Pd(02)ian[Pg.139]

The chemistry of complexes of members of the nickel triad with 1,1-ligands has been studied extensively (1). 

A variety of behaviour is observed in the reactions of [Na(THF)4][cyclo-P5 Bu4] with phosphine halide complexes of the nickel triad." Of particular interest is the formation of the complex Ni(cyclo-P5 Bu3)(PEt3)2 in which the... 

Among the characterized metal homoenolates, only zinc homoenolate of alkyl propionate undergoes substitution reactions with electrophiles under suitable conditions. Two types of metal catalysts, copper(I) and metals of the nickel triad (e.g. Pd), have successfully been used to effect allylation, arylation, and vinylation reactions. 

Heteronuclear Clusters Containing Platinum and the Metals of the Iron, Cobalt, and Nickel Triads... 

Numerous dmit chelates have been synthesized following that route. Although dmit chelates of common metal ions are known, considerable interest has been focused on those of d8 ions (nickel triad). Nickel chelates are listed in Tables 26 and 27. Table 28 summarizes all other salts of bis-chelates of dmit, including the other two elements of nickel triad, palladium and platinum. 

Of the transition metals, the nickel triad has been the most studied in terms of xanthate structures, especially nickel xanthates. Thus, binary xanthate structures are known for all elements with no less than 15 binary nickel xanthate structures known and these aggregate in the solid state in six distinct supramolecular architectures. There is also a rich diversity of adducts as well as mixed-ligand complexes, in particular for nickel. 

A series of nickel triad complexes ML3(allene) (Table VII) were prepared (122, 123, 139) and studied in solution by means of H NMR spectroscopy. Consistent with a planar molecular structure,... 

These reactions demonstrated the selective alkylation of sulfur donors in dithiolene ligands. However, they appeared to be confined to nickel triad dithiolene complexes, and the resulting multidentate sulfur ligand could not be decoordinated. 

The carbonylation of alcohols can proceed with formation of carboxylic acid by catalytic insertion of CO into the carbon-oxygen bond. An alternative reaction gives rise to oxalate or formate esters, when the CO is inserted into the oxygen-hydrogen bond. The members of the nickel triad carbonylate alcohols to give each of these products, and they will be discussed separately. 

An interesting addition reaction has been found with the isocyanide complexes of the nickel triad and dialkylamines [Eq. (142)]. The metal atom is oxidized, with formation of diaminocarbenes (77). The ligand cis to the metal-bonded oxygen is attacked. This is shown in the X-ray structure of 177b (197). 

These conditions are typically fulfilled by transition metals with d8 and dw electron configurations, notably Fe°, Ru°, Os°, Rh1, Ir1, Ni°, Pd°, Ptn, and Pt° (see later for a discussion of Niu/NiIV and Pdn/PdIV). The stability of the higher oxidation states increases within a transition metal triad, so that, for example, Ir111 is more stable than Rh111. This trend is most pronounced for the nickel triad where there are numerous examples of the oxidation of Pt11 to Ptlv but stable products of oxidative addition to Pd11 have only recently been discovered. 

The area of alkyne cluster chemistry has been the subject of two previous review articles. The first is concerned largely with alkyne-cobalt chemistry (16), while the second provides a comprehensive, systematic review of alkyne-substituted homo- and heterome-tallic carbonyl clusters of the iron, cobalt, and nickel triads (17). This latter review covers the literature up to the end of 1981. The present work does not set out to be fully comprehensive, but rather reflects the authors own interests in the subject. A number of key examples are... 

The N,0,P phosphine-imine-alcohol donor (122) forms simple square-planar complexes with M ions of the nickel triad. The analogous ether (123) acts as a terdentate ligand to Pd, with CH3 in the fourth site of the square-planar complex. ... 

In the next sections, the synthesis, reactions, and relevance to catalysis of hydro complexes of the nickel triad are discussed. A short section on spectroscopy of these compounds is included, along with an extensive table of hydro complexes that have been characterized or isolated. 

In Section II,C, the oxidative-addition reaction of protonic acids to low-valent complexes was discussed. This reaction can lead to formation of either the hydro complex or to the bis complex of the conjugate base. Both of these reactions have been reported for the addition of silanes to low-valent complexes of the nickel triad (73, 74). It is to be expected that the nature of the product will depend on the strength of the acid HX and the trans influence of the conjugate base X. If the acid is strong and the conjugate base has a large trans influence, then it would be anticipated... 

Addition of active methylene compounds to butadiene has been catalyzed by complexes of the nickel triad. A catalyst mixture of Ni(acac)2, PPr(OR )2, and borohydride was effective for the addition of R1R2CH2 (Ri = Ph, R2 = COCH3 Ri = Ph, R2 = CN Ri = Ra = COgEt Ri = COCH3, Rg = COgEt) to butadiene 26). Both Pd(0) and Pd(II) complexes are effective as catalysts for the addition of active methylene compounds such as 2,4-pentanedione and ethyl acetoacetate to butadiene 177, 269). Several products were obtained from these reactions since both the 1 1 and 1 2 addition occurred. 

M. Kumada Some reactions involving silicon and metal complexes of the nickel triad. 

Halogen oxidation of planar complexes, particularly of the nickel triads that contain bidentate glyoximes or macrocyclic ligands, such as, phthalocyanines, substituted porphyrins, or tetraazaannulenes, leads to highly conducting substances that may possess chains of metal atoms as well as chains of polyhalides ... 

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