Nickel triad complexes

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

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,... 

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... 

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. 

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. 

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). 

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 ... 

Collaborative Research with Chatt on the Kinetic Trans Effect of the Nickel Triad Metal Complexes... 

By the late 1950s, Chatt and Bernard Shaw had succeeded in preparing several alkyl-, aryl- and hydrido-metal complexes of the nickel triad. Because of our mutual interest in the kinetic trans effect of platinum(ii) complexes, Chatt and I decided to examine the rates of ligand substitution of these new organometallics. Shaw prepared the compounds and Harry Gray did the kinetic studies. Years later Chatt gave the following account of why the research was so rapidly accomplished. 

The stable cobalt complex LI is prepared by cocondensing cobalt atoms and butadiene at liquid nitrogen temperature This technique is also used to prepare 7t-allyl complexes of the nickel triad metals, e.g., LII . Metal hydrides are intermediates in these reactions , as shown by the reaction of nickel hydrides with dienes to yield rt-allyl complexes . The 7i-allyl complex LIII may be prepared by adding HCl and butadiene to (PPh3)4Ni in toluene or THF at —78°C, then warming to RT . ... 

Carbon disulfide reacts with a wide range of bases to produce ligands which readily coordinate to metals. New synthetic work including the formation of aryl xanthates, disulfide products, and oxidized metal dithiolates is reviewed. The sulfur addition and abstraction reactions are discussed, along with the photobleaching reaction of [Ni(n-butyldtc)a] Bridged mercaptide complexes of nickel triad elements are also described. 

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