Copper complexes 1,1-dithiolates

Many free-radical scavengers (including dithiols and dithiocarbamates) have potential therapeutic usefulness as radioprotective agents. Copper complexes are known to be scavenging agents for the superoxide radical, which is believed to play a role in the induction of radiation damage. The toxic effects of superoxide are believed to lie in its ability to reduce metal ions, for example Cu(II) to Cu(I),... 

Synthesis. These macrocycles are prepared from seven-membered ring dinitrile complexes, 84a-84c (Scheme 17), which contain either methylene, sulfur or oxygen in the five position (129). These cyclic dinitriles are synthesized by alkylating maleonitrile dithiolate or derivatives thereof with the corresponding dihalide. The dinitriles 84a-84c can be cyclized in magnesium propoxide to form porphyrazines 85a (33%), 85b (19%), and 85c (27%) (Scheme 17), which can be demetalated with trifluoroacetic to form 86a-86c. Additionally, 86a has been remetalated with nickel (87a, 92%), copper (88a, 95%), and zinc (89a, 94%). The sulfur and oxygen derivatives 85b, 85c, 86b, and 86c are of low solubility and are not suitable for further manipulation. 

Figure 7.48 Two cytochrome c oxidase Cua center model compounds (A) delocalized core with two i-l,3-(KN KO)-ureate bridges as reported in reference 165-and (B) a dithiolate-bridged mixed-valence binuclear copper ion complex as re in reference 166.

In fact, this 1 1 complex Cu+DDC serves as a "copper carrier", bringing it to the copper-susceptible intracellular system, which is the dithiol compound lipoic acid or the dithiol system lipoic acid dehydrogenase ... 

Relevant to the conflicting reports of copper versns nickel reqnirements for enzyme activity,biochemical stndies demonstrated the existence of a labile nickel associated with the a snbnnit of ACS/CODH. Very recently, model stndies on a metal-ion captnre of a peptide-backbone, nonlabile [MN2S2] (26) nnit have established the capability of snch a nickel dithiolate to bind exogeneons metals. A qualitative ranking of the binding ability of complex (26) with Zn +, Cn+, and Ni + was established by a metal-ion displacement experiment (Zn + < < Cn+), as shown in Scheme 9. ... 

These collectors are effective only under oxidizing conditions, and it is generally accepted that the species that confers hydrophobicity on the mineral surface is either a chemisorbed metal thio compound or the oxidized form of the collector, dithiolate. The amounts of each species formed will depend on the relative stabilities of the metal—sulfur and sulfur—sulfur bonds. The formation of four-membered chelate rings is also possible with soft metal ions such as copper(I) because the largely covalent character of the bond in this instance is able to overcome the strain within the ring by extensive electron delocalization. This could account for the >artial selectivity of some of these reagents for the copper minerals, which has been put to good use in the sequential flotation of copjrer, lead and zinc from complex sulfide ores. ... 

Adducts of the l,2-dithiole-3-thione with silver nitrate and copper dichloride have been described, and for various l,2-dithiole-3-thiones, adducts containing iron, cobalt, nickel, and copper have been studied in more detail. The ligands (L) used are either unsubstituted l,2-dithiole-3-thione or its methyl- or aryl-substituted derivatives. If X represents a halogen atom, the following types of coordination compounds have been characterized CuXLj and CuXLa, FeXjLj, CoXaL, and NiX Lj. Complexes of titanium(III), tin(IV), antimony(III) and (V), and bismuth(III) have also been studied. ... 

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