Cadmium complexes reactivity

The easily prepared, stable solid reagent diphenylamine-borane (Ph2NH BH8) has been shown to be more reactive than aliphatic amine-boranes and almost as reactive as borane-THF for the reduction of ketones acids are also reduced to alcohols. Polyethylene glycols (PEG) catalyse the reduction of ketones by sodium borohydride under phase-transfer (PT) conditions, for example in solid-liquid PT with PEG as solvent. The solid zinc borohydride-dimethylformamide complex reduces aldehydes and ketones to alcohols, but only one hydrogen atom from each tetrahydridoborate unit is utilized. The different rates of reduction of various classes of ketone (saturated aliphatic faster than aromatic, and a -unsaturated very slow) suggest a possible selectivity between ketones. The corresponding cadmium complex, prepared in situ, reacts similarly. Lithium methylborohydride, LiMeBHj, prepared as shown in equation (1), where... 

Abstract This chapter reports an analysis of literature dedicated to the speciation of cadmium in various environmental compartments, i.e., atmosphere, natural waters, soils and sediments. The difficulty of the cadmium speciation studies, due to the variability of composition of different natural systems and to the low cadmium concentration in the environment, is highlighted. As an alternative approach, cadmium behavior is assessed by modelling its reactivity towards the main classes of ligands usually present in natural systems. The stability of cadmium complexes with... 

There are several such toxic agents that cause considerable medical, public and political concern. Two examples are discussed here the heavy metal ions (e.g. lead, mercury, copper, cadmium) and the fluorophosphonates. Heavy metal ions readily form complexes with organic compounds which are lipid soluble so that they readily enter cells, where the ions bind to amino acid groups in the active site of enzymes. These two types of inhibitors are discussed in Boxes 3.5 and 3.6. There is also concern that some chemicals in the environment, (e.g. those found in industrial effluents, rubbish tips and agricultural sprays), although present at very low levels, can react with enhanced reactivity groups in enzymes. Consequently, only minute amounts concentrations are effective inhibitors and therefore can be toxic. It is suggested that they are responsible for some non-specific or even specific diseases (e.g. breast tumours). 

The finely divided cadmium may be stored for several months either as a slurry or in a dry state. (A dry 7 month-old sample was just as reactive as a fresh sample.) Strict anhydrous, airless conditions must be maintained, however. The cadmium crystallite sizes are variable but are generally in the 100-1000 A range. Particle sizes range up to several microns, with some particles even much larger. (Nontransition metals yield more nonuniform particle distributions than transition metals, which form stronger complexes with the solvent). 

A fairly recent development in zinc and cadmium chemistry has been the use of NMR to study the coordination environment of these metals 1L1Cd, 113Cd and 67Zn nuclei have been A structure-reactivity relationship which predicts formation constants of complexes with organic ligands has been put forward.241 ... 

Two aspects of ligand-exchange reactions are under active study at present. The first of these areas is the development of the chemistry of the bis(trifluoromethyl)zinc adducts. Like the cadmium compound, (CF3)2Zn is isolatable only if complexed by 2 mol of base. The (CF3)2Zn 2 pyridine species (101), however, exchanges ligands only at a sluggish rate (113). The adducts of the less basic solvents examined to date yield complexes that are exceedingly reactive but very difficult to purify. 

Zinc-modified cyanoborohydride, prepared from anhydrous zinc chloride and sodium cyanoborohy-dride in the ratio 1 2 in ether, selectively reduced aldehydes and ketones but not acids, anhydrides, esters and tertiary amides. In methanol the reactivity paralleled the unmodified reagent. Zinc and cadmium borohydrides form solid complexes with DMF, which may prove to be convenient sources of the reducing agents.Aromatic and a,p-unsaturated ketones were reduced much more slowly than saturated ketones, so chemoselective reduction should be possible. 

Metal complex formation can be used to stabilize an otherwise reactive or unstable organic developer, such as hydroquinone or p-phenylenediamine, to permit its incorporation into silver halide emulsion layers or adjacent layers. For example, catechols and hydroquinones can be mixed with several metal salts of lead(II), cadmium or barium and incorporated into emulsion layers. Treating the film with an activator solution containing an anion that forms an insoluble salt of the metal ion (S04 , liberates the organic developer.The structures of the complexes... 

Analysis of the Structures. In the following, questions concerning the stereoregularity of the polymer and the origin of the photoinactivity of the copper salts will be answered. For this purpose, the crystal structures of the reactive cadmium chloride complex salt 2 as monomer and polymer, and of the corresponding copper salt i. have been solved by x-ray diffraction. 

Burton, D.J., Takei, R., and Shin-Ya, S., Preparation, stability, reactivity and synthetic utility of a cadmium stabilized complex of difluoromethylene phosphonic acid ester, J. Eluorine Chem., 18, 197, 1981. 

---