Thallium-nitrogen bonds

Taylor, E.C., Altland, H.W., Kienzle, F., and McKillop, A., Thallium in organic synthesis. XLl. Synthesis of 1-substituted 2(lH)-pyridones. New synthesis of unsymmetrical biphenyls via photochemical nitrogen-oxygen bond cleavage of l-aroyloxy-2(liJ)-pyridones, /. Org. Chem., 41, 24-27, 1976. 

The ylides have been classified on the basis of the heteroalom covalently bonded to the carbanion. Accordingly, they can be differentiated into nitrogen ylide (Scheme 2), sulfur ylide Scheme 3, phosphorus ylide Scheme 4, arsenic ylide Scheme 5, antimony ylide (Scheme 6), bismuth ylide (Scheme 7) and thallium ylide (Scheme 8). 

Metal-Nitrogen Bond Lengths and Torsion Angles between the Metal and Nitrogen Coordination Planes for Three-Coordinate Aluminum, Gallium, Indium, and Thallium Amides... 

Figure 8.12 An illustration of the planar (TIN)2 ring in the compound [(TI N(SiMe3)2 )2]. Thallium, nitrogen and silicon atoms are shown as black spheres and carbon atoms are white. Selected bond lengths TI1-N1 2.581(7), TI1-N2 2.576(7) A...

When oxygen, nitrogen, and sulfur bound to organic groups are also bound to Tl1, the Tl—X bond appears to be more covalent than the bond to alkali metal ions in similar compounds. Thallium compounds tend to be polymeric rather than ionic. Thus the acetylacetonate is a linear polymer with 4-coordinate Tl. 

The compounds [CymB(Pz)3]Tl (136) and [FcB(Pz)3]Tl show polymeric structures, with bridging B(Pz)3 fragments in the solid state. This is a result of unfavorable steric interaction between the substituent on boron and the hydrogen atoms on the pyrazolyl ring 5-position. The structure of [Cym B(Pz)3]Tl is somewhat related, but it adopts a macrocyclic tetrameric structure rather than a linear polymeric structure. Ligands with secondary donors on the backbone may form additional bonds to the thallium atom. For example, in [HB(3-(2-pyridyl)Pz)3]Tl, weak TF"N interactions between pyridyl nitrogens and the T1 atom have been observed. HB(3-(2-MeOC6Fl4)Pz)3]Tl features close intramolecular TF 0 interactions. ... 

---