Nickel complexes behavior

For PR3/P(OR)3-stabilized nickel complexes, there are two borderline cases known from the experimental investigation of Heimbach et al. 1 which, unlike the usual behavior, redirect the cyclo-oligomerization reaction into the Ci2-cyclo-oligomer production channel. Catalysts bearing either strong a-donor ligands that must also introduce severe steric pressure (e.g., PBu Pr2) or sterically compact n-acceptors (like P(OMe)3) are known to yield CDT as the predominant product. From a statistical analysis it was concluded,8a,8c that the C8 Ci2-cyclo-oligomer product ratio is mainly determined by steric factors (75%) with electronic factors are less important. 

In the presence of PhBr and PhCH2Br, both Ni(BF4)2(bipy)3 and NiCl2(bipy) showed classical catalytic behavior. A peak for the product of the first oxidative addition of the reduced nickel complex appeared at p = —1.4 to —1.5V when the reactant was Ar(Ni)Br. In this case, the electrochemical catalysis was carried out by maintaining the potential of the working electrode at E" = —1.4 V vs. silver. 

The structure of complex behavior in anodic nickel dissolution was analyzed and... 

We can now make sensible guesses as to the order of rate constant for water replacement from coordination complexes of the metals tabulated. (With the formation of fused rings these relationships may no longer apply. Consider, for example, the slow reactions of metal ions with porphyrine derivatives (20) or with tetrasulfonated phthalocyanine, where the rate determining step in the incorporation of metal ion is the dissociation of the pyrrole N-H bond (164).) The reason for many earlier (mostly qualitative) observations on the behavior of complex ions can now be understood. The relative reaction rates of cations with the anion of thenoyltrifluoroacetone (113) and metal-aqua water exchange data from NMR studies (69) are much as expected. The rapid exchange of CN " with Hg(CN)4 2 or Zn(CN)4-2 or the very slow Hg(CN)+, Hg+2 isotopic exchange can be understood, when the dissociative rate constants are estimated. Reactions of the type M+a + L b = ML+(a "b) can be justifiably assumed rapid in the proposed mechanisms for the redox reactions of iron(III) with iodide (47) or thiosulfate (93) ions or when copper(II) reacts with cyanide ions (9). Finally relations between kinetic and thermodynamic parameters are shown by a variety of complex ions since the dissociation rate constant dominates the thermodynamic stability constant of the complex (127). A recently observed linear relation between the rate constant for dissociation of nickel complexes with a variety of pyridine bases and the acidity constant of the base arises from the constancy of the formation rate constant for these complexes (87). 

Dynamic behavior in solution is revealed by variable temperature NMR measurements and is primarily due to inversion at sulfur. The trans-anti and trans-syn isomers are the major species in the solution of the nickel complex. In solutions of Pd and Pt complexes, the cis-anti isomers are also detectable. The cis-anti isomer of the Pt complex has been isolated and is more stable than that of the Pd analogue (64). Hypothetically, a fourth isomer, the cis-syn isomer, may also exist. However, this species may not be stable even at temperatures as low as —50 °C. Inspection of the crystal structure of the trans-anti isomer... 

For the sake of completeness, nickel complexes with bis(thiosquaramide) ligands such as [Ni(sq— S4XI2 (sq = squaric acid) (45) are to be noted. They exhibit thermochromic behavior in pyridine solution. Their dinuclear structure is concluded from elemental analyses and spectroscopic data. Complexes such as [Ni(S20—H)2] serve as stabilizers in color photography (46a). They are assumed to exhibit six-coordinate Ni(II) centers. 

Figure 1. Thin-layer chromatographic behavior of nickel complexes with exocellular fungal metabolites (a) before and (b) after elution through soil. Nickel was visualized by autoradiography intensity is directly related to nickel concentration.

Even when considered on a long term basis, there is considerable doubt that the presence of land filled battery metals such as lead, zinc, and cadmium would have the catastrophic environmental effects which some have predicted. Studies on 2000-year old Roman artifacts in the United Kingdom (Thornton 1995) have shown that zinc, lead and cadmium diffuse only very short distances in soils, depending on soil type, soil pH and other site-specific factors, even after burial for periods up to 1900 years. Another study in Japan (Oda 1990) examined nickel-cadmium batteries buried in Japanese soils to detect any diffusion of nickel or cadmium from the battery. None has been detected after almost 20 years exposure. Further, it is unclear given the chemical complexation behavior of the metallie ions of many battery metals exactly how they would behave even if metallic ions were released. Some studies have suggested, for example, that both lead and cadmium exhibit a marked tendency to complex in sediments and be unavailable for plant or animal uptake. In addition, plant and animal uptake of metals such as zinc, lead and cadmium has been found to depend very much on the presence of other elements such as iron and on dissolved organic matter (Cook and Morrow 1995). Until these behavior are better understood, it is unjustified to equate the mere presence of a hazardous material in a battery with the true risk associated with that battery. Unfortunately, this is exactly the method which has been too often adopted in comparison of battery systems, so that the true risks remain largely obscured. 

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