Cadmium complexes thiols

The first example of utilizing a cadmium complex as a catalyst in enan-tioselective reaction was conjugate additions of thiols to cyclic enones and enals catalyzed by chiral iV -dioxide-cadmium iodide complex. The sulfides are generated in high yields and in good enantioselectivities up to 78% ee (323). 

The other characteristic feature of the thiol donor group in cadmium complexes is the formation of oligomeric structures. The existence of Cd2Ls was detected in the cadmium(ll)-cysteine and -cysteine-methylester system. 

Swayambunathan V, Hayes D, Schmidt KH, Liao YX, Meisel D (1990) Thiol surface complexation on growing cadmium sulfide clusters. J Am Chem Soc 112 3831-3837... 

As expected, the formation of ZnS-(GSH) nanoclusters is analogous to CdS. Beginning with the Zn(II)(GSH)2 precursor complex, nanocluster formation is initiated by the addition of the sulfide. Mehra et al. has shown that the precursor Zn(II)GSH complex does indeed closely follow the synthetic route of CdS-(GSH) nanoparticles. Considering the similarities between the thiol chemistry of zinc and cadmium, studies to optimize ZnS nanocluster formation primarily focused on the ratio of zinc to sulfide ions in solution. Varying equivalents of sulfide (0.1-2.0) were studied for the formation of nanoclusters. An optimal ratio of Zn + S was obtained at 1 1. The average size of nanoparticles prepared at this ratio was shown to be about 3.45 0.5nm. Elution profiles from SEC highlighted the dispersity of nanoparticle populations synthesized in aqueous solutions. By size dependent absorption, the reaction mixtures revealed two cluster populations with an approximate diameter of 22.6 A and 19.54 A, respectively. Any excess of sulfide added greater than 1 equivalent was volatilized and not incorporated into the nanoclusters. ... 

Many dithiocarbamate complexes of zinc, silver, cadmium or mercury improve emulsion stability, including bis(dibenzyldithiocarbamato)-zinc(II) or -cadmium(II) and silver(I) diethyldi-thiocarbamate. Cadmium salts, mixed with citric acid or tartaric acid and added to the emulsion, are reported to be effective. Mercury(II) complexes of ethylenediaminetetraacetic acid (EDTA) and related ligands and of solubilized thiols such as (4) can be used. Other coordination compounds reported include EDTA and related ligand complexes of Co and Mn, mixtures of Co salts with penicillamine (5) and macrocyclic complexes of Ag such as (6). The latter compounds may be used in diffusion transfer systems in which transferred maximum densities are stabilized. 

Mercury showed the highest toxicity of all metals examined (Nies 1999). The Hg(II) cation diffuses into the cells as a hydroxo-complex and adheres to thiols. For efficient detoxification, Hg(II) is actively imported into bacterial cells and reduced to the metallic form, which then diffuses out of the cell and its environment. Due to their toxicity, mercury is not a trace element, and cadmium is only one under rare conditions (Brown et al. 2002a). 

Frenkel AI, Vairavamurthy A, Newville M (2001) A study of the coordination environment in aqueous cadmium-thiol complexes by EXAFS spectroscopy experimental vs theoretical standards. J Synchrotron Rad 8 669-671... 

These Fp-alkene complexes react with a variety of other nucleophiles,3 5 including water, alcohols, amines,3 6 phosphines, and thiols as well as carbon nucleophiles (enamines, organocuprates, enolates),3 2,3l8 and dialkyl cadmium reagents.3 9 Diene complexes such as 487 were converted to the corresponding cationic complexes (488), for example, and reaction with malonate gave 489. The iron complex was removed with trimethylamine N-oxide (Me N-O) to give 490.320... 

Other Preparations.—Carboxylic acids have been converted into aldehydes through di-isobutylaluminium hydride reduction of 3-acylthiazolidine or 2-thiazoline-2-thiol ester intermediates. Bis(triphenylphosphine)copper(l) tetrahydroborate, (Ph3P)2CuBH4, shows promise as a new reagent for the reduction of acid chlorides to aldehydes. The same conversion can be accomplished using sodium borohydride in a mixture of acetonitrile and hexamethyl-phosphoramide containing a cadmium(il) chloride-dimethylformamide complex. ... 

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