Xanthates transition metals

Organosulfur Adsorbates on Metal and Semiconductor Surfaces. Sulfur compounds (qv) and selenium compounds (qv) have a strong affinity for transition metal surfaces (206—211). The number of reported surface-active organosulfur compounds that form monolayers on gold includes di- -alkyl sulfide (212,213), di- -alkyl disulfides (108), thiophenols (214,215), mercaptopyridines (216), mercaptoanilines (217), thiophenes (217), cysteines (218,219), xanthates (220), thiocarbaminates (220), thiocarbamates (221), thioureas (222), mercaptoimidazoles (223—225), and alkaneselenoles (226) (Fig. 11). However, the most studied, and probably most understood, SAM is that of alkanethiolates on Au(lll) surfaces. 

Pyridazines form complexes with iodine, iodine monochloride, bromine, nickel(II) ethyl xanthate, iron carbonyls, iron carbonyl and triphenylphosphine, boron trihalides, silver salts, mercury(I) salts, iridium and ruthenium salts, chromium carbonyl and transition metals, and pentammine complexes of osmium(II) and osmium(III) (79ACS(A)125). Pyridazine N- oxide and its methyl and phenyl substituted derivatives form copper complexes (78TL1979). 

Metal complexes of ligands containing a sulfur donor in conjunction with nitrogen, oxygen or a second sulfur have been reviewed in the past [11-13]. For example, reviews of the coordination compounds of dithiophosphates [14], dithiocarbamates [15, 16], dithiolates [17], dithiodiketonates [18], and xanthates [16] have appeared. The analytical aspects [19] and the spectral and structural information of transition metal complexes of thiosemicarbazones [20, 21] have been reviewed previously. Recent developments in the structural nature of metal complexes of 2-heterocyclic thiosemicarbazones and S-alkyldithiocarbazates, depicted below, are correlated to their biological activities. 

The ligand field strength of the ligands is between that of the dithiocarbamates and water.49 IR studies show characteristic bands near 1250, 1100, 1020 and 550 cm-1.93 The contribution of the resonance form (85) in transition metal complexes is less than that of the analogous structure in the dithiocarbamates.60 The electron density on the metal is not very high, which accounts for the fact that abnormal high oxidation states are exceptional and a strong interaction of bases with the square planar nickel (and some other metal) xanthates is found.94... 

The metal complexes of diethyl dithiophosphate were first investigated in 1931,134 when it was shown that the transition metal complexes [M((EtO)2PS2 ] (n = 2 or 3) were similar to those of xanthates and dialkyl dithiocarbamates, containing a four-membered XSMS (X = C or P) ring. A... 

Of the transition metals, the nickel triad has been the most studied in terms of xanthate structures, especially nickel xanthates. Thus, binary xanthate structures are known for all elements with no less than 15 binary nickel xanthate structures known and these aggregate in the solid state in six distinct supramolecular architectures. There is also a rich diversity of adducts as well as mixed-ligand complexes, in particular for nickel. 

For rayon production, a controlled cleavage of the cellulose molecule is required to reduce the viscosity of the cellulose xanthate so that it can be forced through fine spinnerets. A similar reduction of viscosity is required for cellulose which will be sprayed as a lacquer. This cleavage is brought about by the air oxidation of alkali cellulose, and the process is speeded by the addition of a few parts per million of a transition metal compound which functions as an oxidation catalyst. 

The use of sulfones as relays can be extended to the introduction of a large variety of appendages. Vinylation is especially important because of the general difficulty of performing vinylations on sp centres using transition metal chemistry. The examples assembled in Scheme 14 thus acquire a special significance [31]. It is also noteworthy that both the allylation and vinylation reactions, as well as some of the more exotic transformations discussed later in this section, all of which employ sulfone-based reagents, can be applied not just to aliphatic xanthates but also to iodides and tellurides [29,37-44]. 

Dithiocarbamates form a wide range of complexes with transition metals, and compounds of other metals such as Sn and of non-metals such as Te are also known. The CS2 group in dithiocarbamates as well as in xanthates, thioxanthates, and thiocarbonates is usually chelated as in (10-XIX), but a few cases of monodentate dithiocarbamates are known.39... 

There has been a review of the use of transition-metal catalysts in the formation of C—S, C—Se, and C—Te bonds." Copper catalysis enables the formation of unsymmetrical diaryl thioethers from two differently substituted aryl iodides using ethylxanthogenate as the source of sulfur. Initial formation of an aryl xanthate, such as (17), is followed by hydrolysis to the arenethiolate, which couples with the second aryl iodide." Copper catalysis has also been used in the methylthiolation of aryl halides by DMSO. The method requires the presence of a source of fluoride ions, such as zinc fluoride." In the presence of a palladium catalyst, the reaction of aryl and heteroaryl bromides with AgSCp3 gives the corresponding trifluoromethylsulfldes." ... 

The preparations of some new transition-metal complexes of xanthates have been described recently. - ... 

The xanthates are compounds of the type ROCSS , usually available as alkali metal salts. They form water insoluble complexes with a wide range of transition metal ions, which are readily extracted into organic solvents. 

---