Nickel group metals, complexes with

Perchlorate ion complexes, 28 255-299 with cobalt group metals, 28 265-268 coordination types, 28 256-260 with copper group metals, 28 273-283 with early transition metals, 28 260-263 electronic spectra. 28 258-259 ESR spectra, 28 260 infrared and Raman spectra, 28 257-258 with iron group metals, 28 263-265 with lanthanides, 28 260-265, 287-288 magnetic susceptibility, 28 260 molar conductivities, 28 260 with nickel group metals. 28 268-273 X-ray crystal structure analysis, 28 256-257... 

Alkenes. Most Group VIII metals, metal salts, and complexes may be used as catalyst in hydrosilylation of alkenes. Platinum and its derivatives show the highest activity. Rhodium, nickel, and palladium complexes, although less active, may exhibit unique selectivities. The addition is exothermic and it is usually performed without a solvent. Transition-metal complexes with chiral ligands may be employed in asymmetric hydrosilylation 406,422... 

Metal complexes with fluoro-/3-diketones have been comprehensively reviewed.1585 The introduction of electron-withdrawing groups in the chelate ring increases the Lewis acidity strength of the ML2 complexes, and consequently the bis adducts of the fluoro-/3-diketonato complexes are more stable than the corresponding complexes with /3-diketones. As an example of a nickel complex with 1,1,1-trifluoroacetylacetone which does not have a counterpart in the nickel acetylacetonate complexes we can mention the hexanuclear complex Ni6Lio(OH)2(H20)2.1586... 

Mechanistic studies from Semmelhack s group showed that in the first step aryl halide undergoes oxidative addition to the low valent metal complex with formation of organometallic intermediate in a higher oxidation state [1,2]. For example, bis(l,5-cyclooctadienyl)nickel(0), Ni(COD)2, reacts with aryl halide (I) to give arylnickel(II) halide (VIII), which further reacts with another aryl halide molecule to form diarylnickel(IV) halide (IX). Each oxidative addition step includes substitution of ligands at metallic centre. 1,5-Cyclooctadiene (COD) dissociates from the nickel to form a coordinatively unsaturated metallic-centre, which does react with aryl halide. Biaryl II is formed by reductive elimination step from IX with liberation of nickel(II) halide [1,2], Scheme 1. 

Dehalogenation of monochlorotoluenes can be readily effected with hydrogen and noble metal catalysts (34). Conversion of -chlorotoluene to Ncyanotoluene is accompHshed by reaction with tetraethyl ammonium cyanide and zero-valent Group (VIII) metal complexes, such as those of nickel or palladium (35). The reaction proceeds by initial oxidative addition of the aryl haHde to the zerovalent metal complex, followed by attack of cyanide ion on the metal and reductive elimination of the aryl cyanide. Methylstyrene is prepared from -chlorotoluene by a vinylation reaction using ethylene as the reagent and a catalyst derived from zinc, a triarylphosphine, and a nickel salt (36). 

In a nickel-containing enzyme various groups of atoms in the enzyme form a complex with the metal, which was found to be in the +2 oxidation state and to have no unpaired electrons. What is the most probable geometry of the Ni2+ complex (a) octahedral (b) tetrahedral (c) square planar (see Exercise 16.96) Justify your answer by drawing the orbital energy-level diagram of the ion. 

In nickel and palladium dithiobenzoato complexes, four-membered chelate rings are formed (366), whereas, in the corresponding phenyl-dithio acetates [M2(S2CCH2Ph)4], the dithio ligands act as bridging groups between the two metal atoms, with the formation of binuclear units (367). The molecular structure of the latter compounds shows that each metal atom is coordinated to four sulfur atoms and to the other metal atoms in a square-pyramidal geometry. Other evidence for... 

A novel polysiloxane, containing the isocyanide group pendent to the backbone, has been synthesized. It is observed to react with the metal vapors of chromium, iron and nickel to afford binary metal complexes of the type M(CN-[P])n, where n = 6, 5, 4 respectively, in which the polymer-attached isocyanide group provides the stabilization for the metal center. The product obtained from the reaction with Fe was found to be photosensitive yielding the Fe2(CN-[P])q species and extensive cross-linking of the polymer. The Cr and Ni products were able to be oxidized on exposure of thin films to the air, or electrochemically in the presence of an electron relay. The availability of different oxidation states for the metals in these new materials gives hope that novel redox-active polymers may be accessible. 

Many carbonyl and carbonyl metallate complexes of the second and third row, in low oxidation states, are basic in nature and, for this reason, adequate intermediates for the formation of metal— metal bonds of a donor-acceptor nature. Furthermore, the structural similarity and isolobal relationship between the proton and group 11 cations has lead to the synthesis of a high number of cluster complexes with silver—metal bonds.1534"1535 Thus, silver(I) binds to ruthenium,15 1556 osmium,1557-1560 rhodium,1561,1562 iron,1563-1572 cobalt,1573 chromium, molybdenum, or tungsten,1574-1576 rhe-nium, niobium or tantalum, or nickel. Some examples are shown in Figure 17. 

Penicillamine is known to form complexes of varying stability with several metal ions. In neutral solution, penicillamine complexes with mercury, lead, nickel, and copper are relatively more stable than those of zinc, iron, and manganese. The three functional groups of penicillamine may be engaged in the formation of metal complex, and the resultant compounds may be polymeric in structure. 

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