Carbonyl, addition thallium

Thallium(i) salts have long been used in reactions with organic and organometallic halide complexes as a means of activating the halide by removal as insoluble T1X. However, the thallium ions proved not to be innocent bystanders, and numerous examples were reported in COMC (1995) where the metal-bound thallium complexes were formed. Deliberate reactions of thallium(i) and thallium(m) salts with metal carbonyl anions have yielded a variety of complexes of the form T1 MLJ3. In the past decade, new examples of metal carbonyl derivatives of thallium have been prepared (see Table 2). In addition, the propensity for Tl+ to form adducts with 16-electron noble metal complexes has been exploited. 

The most extensive series of compounds that fall within this section are the anionic iron carbonyl-thallium clusters recently described by Whitmire (30-30h). These are generally made by reactions between iron carbonylate anions and either T1(I) or Tl(III) salts. Thus treatment of K[HFe(CO)4] with a variety of thallium salts followed by addition of [Et4N]Cl or Br affords the hexanuclear complex [Et4N]2[ Fe(CO)4 2 //-TlFe(CO)4 2], 17... 

The mixed anhydrides of diphenylphosphinous acid and heavily substituted alkenoic acids displace one PPh3 ligand from [RhCl(PPh3)3] to form a complex where the anhydride is coordinated through phosphorus. If these products are treated with thallium(I) or silver(I) salts, the anhydride coordinates additionally through the carbonyl oxygen and the chloro ligand is displaced. 

The direct conversion of carbyne complexes TpW( = CR)(CO)2 (R = Ph, C6H4Me-4) to cationic c/ -dicarbonyl -phosphinocarbene (metallaphosphacyclo-propene) complexes can be achieved by the addition of chlorodiorganophosphines in the presence of sodium tetraphenylborate or thallium hexafluorophosphate (Scheme 51)/ In the absence of these sodium salts, nucleophile (Cl )-induced carbonyl-carbene coupling affords neutral -phosphinoketene complexes. 

Carbon-heteroatom double bonds can also participate in this reaction. These include both carbonyl compounds (Scheme 11.37) and imines (Scheme 11.38). Addition to aldehydes is co-catalysed by tin(II) or indium(III) salts. Under these conditions, tetrahydrofiirans are obtained. The presence or absence of the co-catalyst can also switch the reaction from one mode to another (Scheme 11.39). An indium cocatalysed cycloaddition to a 7-pyrone aldehyde 11.117 was used in a synthesis of aureothin 11.122 and A-acetylaureothamine 11.123 (Scheme 11.40). Cross-metathesis of the exo-cyc ic alkene 11.118 allowed a subsequent Suzuki coupling with a gem-dibromide 11.120 that showed the expected selectivity (Section 2.1.4.2). This reaction required the use of thallium ethoxide as the Lewis base to suppress the formation of side products. A Negishi coupling completed the synthesis of aureothin 11.122. Reduction and acylation of the nitro group yielded A-acetylaureothamine 11.123. The latter compound is active digainst Helicobacter pylori, a bacterium behind stomach ulcers. 

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