Heterocyclic thiones, complexes

An example of thione coordination is demonstrated with the thiocarbonyl donor ligand 2,6-dimethyl-4H-pyran-4-thione, that gives a complex with zinc chloride of the form ZnL2Cl2-The crystal structure shows the zinc is tetrahedrally coordinated by two chloride and two sulfur donors and the compound was further studied by 3H NMR and IR spectroscopy.573 Both monomeric and dimeric heterocyclic thione complexes have been formed with zinc.5 4,575... 

Neutral Au(I) pentafluorophenyl complexes with heterocyclic thiones can be prepared by displacement of the tht ligand in [Au(QF5)(tht)] with a thione [49] as shown in Equation 3.6. 

Af-Heterocyclic carbene complexes of sulfur or, more simply, imidaz-ole-2-thiones, have been known for many years (51, 52) and have... 

Heterocyclic thiones have been extensively studied because of their facility to yield coordination complexes. All the ligands contain thione and occasionally thiol (mer-capto) groups directly attached to the carbon atoms of heterocyclic molecules. They have been previously reviewed by Raper in 1985576, and very recently the same author has reviewed28 the copper complexes of heterocyclic thioamides and related ligands. 

Among the heterocyclic thiones, we present in Tables 20-25 the metal complexes of some of the thiocarbonyl ligands most widely used, which are represented in Figure 3. In these tables, data are given from 1988. In the case of copper, only complexes reported since Raper s review28 are given. 

Complexes of heterocyclic thione donors. Coord. Chem. Rev. 61, 115 (1984). 

The formation of four-membered chelate rings involving N and S donors is not unusual and has been observed in several complexes of 2-thiol- or 2-thione-substituted N heterocycles. Foye and Lo reported this form of coordination for a variety of metal chelates of antibacterial heterocyclic thiones. 2-Mercaptobenzimidazole (35 X = NH) was reported to form such chelates with Cu , Al and Fe . Complexes of 2-thiouradl (36), and substituted forms, also have been reported with this bonding mode to these metal ions. The tetrakis chelate of W" with 2-mercaptopyrimidine has been shown to adopt a symmetrical dodecahedral geometry. The mercapto S atom is thought to act as the better t-electron donor with the corresponding aromatic N atom acting as a tc acceptor. 

Garner and Joule next adapted the protected dithiolene strategy to target heterocyclic dithiolene complexes. This approach, first reported in 1988 by Larsen et al is illustrated in Scheme 2.25 with the formation of a cobalt quinoxalyldithiolene complex. Reaction of [CoCp(COD)] (COD = 1,5-cyclooc-tadiene) with 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione (26) affords a quinox-aline dithiolene complex (27) that has been structurally characterized. This cobalt complex undergoes extensive proton-coupled electron transfer process (see Section 2.3.4). This system was further elaborated when the pyrazine ring in 4-(quinoxalin-2-yl)-l,3-dithiole-2-thione 26 was selectively... 

Recent reports on transition metal complexes of 2-heterocyclic thiosemicar-bazones suggest that stereochemistries adopted by these complexes often depend upon the anion of the metal salt used and the nature of the N-substituents. Further, as indicated previously, the charge on the ligand is dictated by the thione-thiol equilibrium which in turn is influenced by the solvent and pH of the preparative medium. Many of the reported complexes have been prepared in mixed aqueous solvents, often with bases added. However, there are few reports in which workers have varied the nature of their preparations to fully explore the potential diversity of these ligands. 

Besides complexes of thiosemicarbazones prepared from nitrogen heterocycles, iron(III) complexes of both 2-formylthiophene thiosemicarbazone, 26, and 2-acetylthiophene thiosemicarbazone, 27, have been isolated [155]. Low spin, distorted octahedral complexes of stoichiometry [Fe(26)2A2]A (A = Cl, Br, SCN) were found to be 1 1 electrolytes in nitromethane. Low spin Fe(27)3A3 (A = Cl, Br, SCN) complexes were also isolated, but their insolubility in organic solvents did not allow molar conductivity measurements. Infrared speetra indicate coordination of both via the azomethine nitrogen and thione sulfur, but not the thiophene sulfur. The thiocyanate complexes have spectral bands at 2065, 770 and 470 cm consistent with N-bonded thiocyanato ligands, but v(FeCl) and v(FeBr) were not assigned due to the large number of bands found in the spectra of the two ligands. 

Pseudooctahedral coordination of rhenium(III) centers has also been found for mixed-ligand complexes with tertiary phosphines and A-heterocyclic thiols which coordinate as their neutral thione tautomers. A representative example with thiazoline-2-thiol (HSthiaz) has been characterized structurally. The paramagnetic complex [ReCl3(HSthiaz)2(PPh3)] (235) contains the HSthiaz ligands in trans position. ... 

The coordination abilities of A-heterocyclic thiols such as 2-thiopyridine, HSpy (66a), 2-mercapto-pyrimidine, Hspym (66b), or 2-mercaptothiazoline (67) with rhenium centers has already been described for oxorhenium(V) complexes is Section 5.3.2.3.L It has been outlined that ligands with five-membered rings preferably coordinate as monodentate neutral thiones whereas chelate formation is possible for mercaptopyridine or mercaptopyrimidine. Similar complex formation... 

The tautomers of azole and azine derivatives, stabilized as a result of complex formation, are widely found [11,15,16,18,261-269]. Thus, the metal-cyclic structures with anionic ligands are formed in chelates of 2-hydroxy- 436, 438) and 2-mercapto-substituted (484, 485) derivatives of these nitrogen-containing heterocycles described above. At the same time, the ketone (thion) isomers are stabilized in molecular adducts. In this respect, the syntheses (4.64) [266], (4.65) [267], and (4.66) [269] are quite representative for this group ... 

Organotin 1,2-dithiolate complexes were featured in many studies the ligands used include aliphatic derivatives, e.g. ethane-1,2-dithiolate -SCH2CH2S-(EDT), -SCH2CHMeS-, alkenyl derivatives, e.g. -SCH=CHS-, maleonitriledithiolate (MNT), aryl derivatives, 1,2--SC6H4S (BDT) and toluene-3,4-dithiolate (TDT), as well as heterocyclic derivatives, l,3-dithiane-2-one-4,5-dithiolate (DMIO) and l,3-dithiane-2-thione-4,5-dithiolate (DMIT)191. 

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