Nickel , ligand exchange reactions

Nickel(II) complexes with /3-ketoamines are, in general, easily prepared. The most useful and general synthetic methods are the following (i) reaction of the preformed ligands with nickel salts in basic solution using water, alcohol or their mixtures as medium (ii) ligand exchange reactions (iii) template reactions. Complexes of type (329) may be sensitive to moisture and are prepared in anhydrous conditions. 

Much more research has been carried out with polymers in which the coordinated metal atom is part of the chain backbone. Typically, the metal atoms are copper, nickel, and cobalt. Oxygen atoms or carbon atoms adjacent to the metal atom provide the electrons required for the coordinate bond.30 Polymers of this type are often rather intractable, for a variety of reasons. Specifically, insolubility can be a problem for species with moderate molecular weights. Also, coordination between chains can cause aggregation, and ligand-exchange reactions with small molecules such as solvents can cause chain scission. However, in some favorable cases, the intramolecular coordination is sufficiently strong for the polymer to be processed by the usual techniques such as spinning into fibers or extrusion into films.30... 

At the present time the preparation of the trifluoromethylated derivatives of low valent transition metals by ligand-exchange reactions appears to be quite general. However, as exemplified by the nickel reaction above, the utility of the method is obviously subject to the inherent stability of the desired product. In many cases, such as the preparation of the trifluoromethyl derivatives of the cyclopentadienyl cobalt system, (CF3)Co(Cp)(CO)I and (CF3)2Co(Cp)(CO), the reaction of the dihalide with (CF3)2Cd glyme represents the simplest reaction... 

Some homoleptic unsymmetrical (dmit/mnt, dmit/tdas) dithiolene nickel complex-based D-A compounds with D = TTF and EDT-TTF also exhibit metal-like conductivity (see Table I) (101). Their molecular structure is shown in Scheme 3. The unsymmetrical tetraalkylammonium salts [MLjLJ- (M = Ni, Pd, Pt) have been prepared by ligand exchange reaction between tetraalkylammonium salts of MLj and ML21 (128, 129) and the D-A compounds have been synthesized by electrooxidation. Among these complexes, only the Ni derivatives exhibit metallic-like properties, namely, TTF[Ni(dmit)(mnt)] (metallic down to --30 K), a-EDT-TTF[Ni(dmit)(mnt)] (metallic down to 30 K), TTF[Ni(dmit)(tdas)] (metallic down to 4.2 K), and EDT-TTF[Ni(dmit)(tdas)] (metallic down to --50 K) (see Table I). The complex ot-EDT-TTF-[Ni(dmit)(mnt)J is isostructural (130) to a-EDT-TTF[Ni(dmit)2)] [ambient pressure superconductor, Section II.B.2 (124)]. Under pressure, conductivity measurements up to 18 kbar show a monotonous decrease of the resistivity but do not reveal any superconducting transition (101). 

The Intimate Mechanism of Replacement in Square-Planar Complexes Platinum(II)-Catalyzed Substitutions of Platinum(IV) Complexes Kinetics of Nickel, Palladium and Platinum Complexes Isomerization Mechanisms of Square-Planar Complexes Anomalies in Ligand Exchange Reactions for Platinum(II) Complexes Inorganic Reaction Mechanisms The CIS and trans Efiects of Ligands... 

The rates of ligand-exchange reactions of solvent molecules bound in the first coordination sphere of nickel(II) ions depend on the natures of the other ligands attached to the metal [Hu 71]. By means of N NMR measurements in systems containing nitrogen donor atoms, Lincoln and West [Li 74] studied how various chelate-forming ligands affect the lability of acetonitrile solvent molecules... 

The substitution of CO in metal carbonyls by olefinic and acetylenic compounds is one of the chief methods for preparing tt complexes of transition metals. Unfortunately this procedure fails almost completely when applied to nickel carbonyl, and this may be one of the reasons why until recently no tt complexes of nickel with olefinic or acetylenic ligands were known. The reasons for this behavior of nickel carbonyl will become clearer, if both its electronic structure and the mechanism of the ligand exchange reactions are considered. 

Ligand exchange reactions with labeled carbon monoxide performed by Basolo and Wojcicki (32) show that the carbonyls V(CO)ft, Cr(CO)6, Mn2(CO)io, and Fe(CO)s exchange CO groups only slowly, whereas Ni(CO)4 and Co2(CO)8 exchange rapidly. The kinetic lability of nickel carbonyl can in part be attributed to the thermodynamic weakness of the Ni—C bonds. The essential point, however, is that the exchange rate is independent of carbon monoxide concentration which supports a dissociative mechanism. 

The corresponding [3 + 2 + 2]- and [2 + 2 + 2 + l]-cyclization reactions between these complexes and alkynes are very efficient in the presence of Ni(0). Transmetallation reactions between chromium Fischer carbene complexes and Ni(cod)2 with formation of nickel carbene intermediates is presumed to be responsible for this transformation. The metal-free cycloadducts are easily obtained by ligand exchange reactions at low GO pressures. A [3-h2]-cyclization reaction of a chromium Fischer carbene complex and allene building blocks was accomplished, using... 

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