Thallium arene complexes

The synthesis and characterization of the monomeric amidinato-indium(I) and thallium(I) complexes [Bu C(NAr)2]M[But(NAr(NHAr)] (M = In, Tl Ar = 2,6-Pr2CgH3) have been reported. Both compounds were isolated as pale yellow crystals in 72-74% yield. These complexes, in which the metal center is chelated by the amidinate ligand in an N, j -arene-fashion (Scheme 33), can be considered as isomers of four-membered Group 13 metal(I) carbene analogs. Theoretical studies have compared the relative energies of both isomeric forms of a model compound, In[HC(NPh)2]. ... 

Phosphonate Arene Osmium(II) Complexes. Benzene osmium(II) phosphonates have been made via the initial reaction of phosphite-containing osmium cations of type 147 with Nal. Demethylation occurs, and the anionic complex 182 is obtained. Protonation with trifluoroacetic afforded adduct 183 which generated complex 184 on treatment with pyridine. The latter was shown to be a precursor of the thallium complex 185 containing the chelating osmium phosphonate 115). 

Two arene cyclopentadienyl osmium complexes of type 191 have been prepared in moderate yields (17-43%) by reacting precursor 144 with thallium cylopentadienide in acetonitrile (73). 

The molecular structure of decabenzylferrocene also helped to explain the rather low solubility of this compound in toluene or benzene, in sharp contrast with the previously found excellent solubility properties of other decabenzylmetallocenes and the pentabenzyl-Cp thallium and indium complexes in these solvents. The steric crowding of the benzyl groups in the ferrocene and their limited mobility leave little space for the solvent arene molecules to interact and subsequently to dissolve the molecule. This is quite similar to the situation encountered in the pentaphenylcyclopenta-dienyl derivatives with their closely packed phenyl rings (see Fig. 3). 

Whilst direct electrophilic hydroxylation of the arylthallium species can be effected using peroxytriflu-oroacetic acid, further oxidation of the phenol to a quinone accompanies this process. This over-oxidation can be avoided by initial transmetallation to a lead species with concomitant reduction of the thallium trifluoroacetate (TTFA) by triphenylphosphine, followed by displacement of the lead by trifluo-roacetate to give the aryl trifluoroacetate. lliis hydroxylation method has yet to find use in the synthesis of molecules which are more complex than simple arenes. 

Figure 5 Ground-state and excited-state similarities of the arene ir-complex of mercury(ll) and thallium(III), as shown by (a) association constants (K) and (b) CT absorption spectra (k )...

However, in certain cases under photolytic conditions, spectra of the corresponding arylmercury radical cations 6 developed, whereas no mercuration occurred in dark [81] signifying collapse of the ArH +,Hg(TFA)2 radical ion pair 4, provides an alternative path way to Wheeland complex 2 and hence to ArHg(TFA) + 6. Arene radical cations can also be generated from arene and thallium(III) tris-(trifluoroacetate) in trifluoroacetic acid [82], but with a different mechanism proposed by Eberson et al. [83]. Oxidation of anthracene showed 9-trifluoroacetoxy and 9,10-bis(trifluoroacetoxy)anthracene [84, 85], benzo[a]pyrene, 7-methylbenzo-[a]pyrene and 12-methylbenzo[a]pyrene yielded radical cations of 7- and/or 12-trifluoroacetates [86], triptycene (9,10-dihydro-9,10-[l,2]benzanthracene) showed... 

A better route is the one shown in Scheme 11. The benzene complex 104 forms readily in near quantitative yield upon heating Ru(III) chloride and 1,3-or 1,4-cyclohexadiene in EtOH. The introduction of the Cp ligand is by hali-de/Mcp exchange. The classic procedure to 105 required a stoichiometric quantity of thallium or silver [103], but a very recent, improved procedure shows that cyclopentadiene/K2C03/ abs. EtOH can be used successfully [104]. Although beyond the scope of this review, it is interesting to note that the much less electrophilic complexes [(arene)Ru(C5Me5)] [PFg] are accessible in a one-pot procedure from RuClj [105]. The sequence Birch reduction/complexa-... 

Calix[4]arene probe 29 [57] (Fig. 28.7), in 1,3-altemate conformation and containing bis(crown-6-ether) and a dansyl group, showed selectivity for thallium (1). The fluorescence titrations of 29 with thallium(I) were performed at pH 3.5, at which the probe is in its midissociated form. The complexation of thallium(I) to probe 29 results in slight quenching and blue shift of the fluorescence emission. This behavior was attributed to both PET in the complex and NH-proton displacement by thallium(I). 

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