Dithiolium diketones

Dithiolium salts and dithio- 3-diketone complexes of the transition metals. T. N. Lockyer and R. L. Martin, Prog. Inorg. Chem., 1980, 27, 223-324 (198). 

Dithiolium Salts and Dithio-j8-diketone Complexes of the Transition Metals 1657... 

The first recorded attempt to prepare a thio derivative of a /1-diketone resulted in the isolation of the colourless dimer (57 R = R = Me) from the reaction of acetylacetone and hydrogen sulfide in hydrochloric acid.243 Similar dimers with various R and R groups have been reported244 and the structure (57) has been confirmed from NMR and MS data.245 Other attempts to prepare dithio-/ -diketones (58) yielded 1,2-dithiolium salts (59).246... 

The MS fragmentation patterns of dithio-/J-diketonato complexes differ from those of both /J-diketonato and monothio-/J-diketonato complexes. The mass spectra of bivalent dithioacetyl-acetonato complexes are characterized by a molecular ion peak M and a much stronger peak for L+ due to the formation of the 3,5-dimethyl-l,2-dithiolium ion another peak at tn/e 96 is due to the loss of HS from the dithiolium cation. The mass spectra of nickel complexes of dithio-/ -diketones are dominated by fragmentation products of the uncomplexed oxidized ligand, which is consistent with the low stability of dithio-/J-diketones and the greater stability of the 1,2-dithiolium... 

A variant of this procedure is the reaction of 1,3-diketones or 1,3-monothiodiketones with P4S10 and treatment with acid.14b However, here again only 3,5-disubstituted 1,2-dithiolium salts with at least one aryl substituent can be made. 

In the presence of hydrogen chloride, a-acetylenic ketones react with thioacetic acid to give a monothio-)S-diketone which is converted to a 1,2-dithiolium ion by phosphorus pentasulfide or hydrogen sulfide. These reactions, which involve some sort of oxidation, are discussed in the next paragraph. 

A widely used sulfurization agent is tetraphosphorus decasulfide, commonly named phosphorus pentasulfide. This reagent has been used with j -diketones, leading to 1,2-dithiolium salts.Yields seem to be improved when a mild oxidizing agent such as iodine is added. A side reaction, common when phosphorus pentasulfide is used, is the dealkyla-... 

Hydrogen disulfide provides appropriate S2 units and readily condenses with phenylpropynyl chloride to form 5-phenyl-l,2-dithiole-3-one (128). 1,3-Diketones or synthetic equivalents form 1,2-dithiolium salts (3) <57AG138, 62JCS5104). Hydrogen polysulfide or diacetyl disulfide can usefully replace the hydrogen disulfide (Scheme 18). 

Hydrolysis of chlorinated dithiolium salts of this type (Section II,B,3) yields chlorinated l,2-dithiol-3-ones which have recently attracted attention because of their fungicidal properties. b. From 1,3-Diketones and 1,3-Monothiodiketonea. According to Leaver and Robertson simple 1,2-dithiolium salts can be obtained by the action of H2S2 on 1,3-diketones in HCl-saturated ether. Although no intermediates have been isolated, these reactions can probably be formally represented by Scheme 1. 

Red-brown crystals of this complex dissolve in chloroform and are reduced further, on shaking the solution with aqueous Na2S204, to give the bis-dithio- -diketone iron(II) complex [Fe(C5H7S2)2], which is very sensitive to reoxidation. A similar complex is postulated by Japanese workers, resulting from the reduction of 3-methyl-5-phenyl-l,2-dithiolium perchlorate in the presence of Fe. The exact structure is unknown but is thought to be as shown in (92). [FeCl4] forms a... 

Further recent papers concerning metal complexes of thio-analogues of j3-diketones deal with the preparation of the cobalt(n) complex of 1,3-diacetylthioacetone, the synthesis and properties of a series of metal complexes of dithioacetylacetone, the synthesis of the nickel(n) complexes of monothio- and dithio-dibenzoylmethane (67) by the nucleophilic cleavage of 1,2-dithiolium salts by hydroxide or mercaptide ions in the presence of nickel(ii) ions, the bromination of the cobalt(m) complex of monothioacetylacetone (68) with iV-bromosuccinimide to yield (69), and the application of monothiodibenzoylmethane as an analytical reagent for quantitative determination of copper. ... 

The synthesis of 1,2-dithiolium salts from /3-diketones has been modified by the use of diacetyl disulphide in place of hydrogen disulphide. Precursors of the general type (30), where Y = O, S, (OEt)a, or N+MCg, and Z = OH, Cl, or OEt, are treated with the diacyl disulphide and a strong acid. This versatile synthesis has been applied to the preparation of a wide range of alkyl- and aryl-substituted dithiolium salts. 

Synthesis.—3,5-Diaryl- and 3,5-dialkyl-1,2-dithiolium salts (121 R = Ar or Bu ) can be prepared in good yield by the sulphurization of diketones (Scheme 9). Treatment of these salts (121) with pyridine affords the corresponding 4-olates (122), which can be O-alkylated with iodomethane and similar compounds. With ammonia, ring scission and re-cyclization occurs, and the corresponding iso-thiazolium-4-olates are formed. An unusual synthesis of 1,2-dithiolium salts (124) is by the photolysis of l,2-dithiole-3-thiones (123) in benzene or acetonitrile, in the presence of aryl or alkenyl bromides or iodides. 

Details have been given of methods for the preparation of 1,2-dithiolium tri-iodides and iodides by the action of hydrogen sulphide and iodine on 1,3-diketones, and the diacetyl disulphide method has been applied to l-acylindan-2-ones, yielding indeno-1,2-dithiolium salts (22), which can be deprotonated to indeno-1,2-dithioIes (23). A mechanistic study has been... 

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