Thallium derivatives

N-Alkylations, especially of oxo-di- and tetra-hydro derivatives, e.g. (28)->(29), have been carried out readily using a variety of reagents such as (usual) alkyl halide/alkali, alkyl sulfate/alkali, alkyl halide, tosylate or sulfate/NaH, trialkyloxonium fluoroborate and other Meerwein-type reagents, alcohols/DCCI, diazoalkanes, alkyl carbonates, oxalates or malon-ates, oxosulfonium ylides, DMF dimethyl acetal, and triethyl orthoformate/AcjO. Also used have been alkyl halide/lithium diisopropylamide and in one case benzyl chloride on the thallium derivative. In neutral conditions 8-alkylation is observed and preparation of some 8-nucleosides has also been reported (78JOC828, 77JOC997, 72JOC3975, 72JOC3980). 

A mild, but more restricted, A -alkylation procedure (Method C) for 5//-dibenz[b,/]azepines involves the action of alkyl halides on their Af-thallium derivatives.190... 

The solution of the thallium derivative 19 in MeCN was treated with KI (0.246 g, 1.5 mmol) in H,0 (1 mL) and the product was extracted into tt20. The extract was washed with H20, dried (MgS04) and chromatographed (silica gel, petroleum ether) to give 20c as pale-yellow plates [yield 0.037 g (80% based on unrecovered 4) mp 92-94 C (petroleum ether)], followed by starting material 4 (0.005 g, 17%). 

Finally, the tris(pyrazolyl)hydroborato ligand system has also provided an interesting example in which a crystallographic site is disordered between a vacancy and a chain of three atoms. Thus, the x-ray structure of the cobalt complex [TpAnt]CoNCS (Ant = 9-anthryl) revealed the presence of the cocrystallized thallium derivative... 

A series of unsymmetric bis(pyrazolylate) ligands have been synthesized and complexed with zinc via metathesis of a thallium derivative, (17) and (18). This allowed the synthesis and complexation of NNS and NNO pyrazolylborate derivatives.1 9,160 Parkin and co-workers synthesized zinc complexes of a series of unsymmetric pyrazole-containing ligands.161-163 The asymmetric bis(pyrazolyl)hydroborato zinc complex has been structurally characterized,164 and will also be discussed in the context of its interaction with the B H hydrogen in Section 6.8.9.2. 

Reaction of the anion 21 with Cp or Cp metal fragments provides further metallocene-type complexes with a pendant phosphaferrocene side-chain. For example, the reaction of the thallium derivative T1 21 with [Cp RhCl2]2 yields the cationic pentamethylrhodocenium 24 as its chloride (Scheme 1.5.10). This is an interesting species because it is a chiral water-soluble P ligand. The chloride anion can be exchanged by PF,s to make the compound more soluble in organic solvents. 

Dialkyl and diarylthallium(III) derivatives are stable, crystalline solids that melt at 180—300°C. The dimethyl thallium derivatives of CN", C10 4, BF 4, and NO 3 contain linear (CH3)2T1 cations and the free anions (19). In aqueous solutions, they ionize to the (CH3)2T1(H20)+ ions, except those derivatives containing alkoxide, mercaptide, or amide anions, which yield dimeric structures (20,21). 

The complexes exhibited different behavior in solution. The gold-thallium derivative showed a shift of the emission to 536 nm when the measurement was carried out in frozen solution. This was explained by a higher aggregation of [Aull(MTP)2] units in the solid state compared to the situation in solution. In the case of the Au-Pb compound, the emission spectrum showed a strong dependence on the aggregation state and temperature. Thus, the emission band in TH F solution, which appeared at 555 nm (298 K) (x = 57 ns), was shifted to 480 nm in frozen solution (x = 2.3 ps) or appeared at 752 nm in solid state (x = 22 ns). As with the thallium complex, the shift to high energy in solution may have been related to the polymeric structure of the complex in the solid state that was not reproduced in solution. 

Lithiation of dibenzofuran with butyllithium and mercuration both occur at the 4-position. Thallation occurs at the 2-position, however (57IZV1391). The mercury and thallium derivatives serve as a source of the iodo compounds by reaction with iodine. Bromodibenzofurans undergo bromine/lithium exchange with butyllithium and the derived lithio compounds may be converted into phenols by reaction with molecular oxygen in the presence of a Grignard reagent, into amines by reaction with O-methylhydroxylamine, into sulfinic acids by reaction with sulfur dioxide, into carboxylic acids by reaction with carbon dioxide and into methyl derivatives by reaction with methyl sulfate (Scheme 100). This last reaction... 

Section II. A regioselective introduction of disilanyl bridges is necessary in the process to synthesize complexes with ligands of types 36 or 37109, and this has been made possible by methylation of the cyclopentadienyl fragments. Due to prototropic rearrangements, the protonated derivatives of 36 and 37 exist as a complicated mixture of isomers. The synthesis of the thallium derivative of 37109 is shown in equation 51. 

Studies have also been carried out by mixing T1(CH3)3 with T1(C2HS)3 in which it is shown that rapid exchange occurs with the formation of the methyl ethyl derivatives 84). No clear attempt has been made to evaluate the mechanism of this reaction but it is certain that all of the mixed thallium derivatives can be prepared. Maher and Evans 82) also examined the... 

The crystalline 0-form of the sugar was first isolated17 by the hydrolysis of the mixture of products obtained by the methylation with methyl iodide of the thallium derivatives of methyl xylopyranosides (aft mixture) in which the 2,4-dimethyl-D-xylose was the principal component. Since the corresponding acid gave a pyranolactone, the amide gave a negative Weerman test and the derivatives in question were different from those of 2,3-dimethyl-D-xylose, the constitution was established. 

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