Thallium(I) Complexes of Tris(pyridyl)borates and a Comparison to Their Pyrazolyl Analogues

Abstract

Thallium(I) complexes of B-methylated and B-phenylated tris(pyridyl)borates featuring trifluoromethyl groups at the pyridyl ring 6positions have been synthesized by metathesis using the corresponding potassium salts [MeB(6-(CF 3 )Py) 3 ]K and [PhB(6-(CF 3 )Py) 3 ]K with thallium(I) acetate. The closely related tris(pyrazolyl)borate analogue [PhB(3-(CF 3 )Pz) 3 ]Tl has also been prepared, and comparisons of structural and spectroscopic features between the two scorpionate families are presented. [MeB(6-(CF 3 )Py) 3 ]Tl displays κ 3 -coordination of the tris(pyridyl)borate similar to that of tris(pyrazolyl)borate in [MeB(3-(CF 3 )Pz) 3 ]Tl, while [PhB(6-(CF 3 )Py) 3 ]Tl and [PhB(3-(CF 3 )Pz) 3 ]Tl feature κ 2 -N,N ligand coordination modes with the B-phenyl groups flanking the thallium sites. 19 F NMR spectroscopy of [MeB(6-(CF 3 )Py) 3 ]Tl reveals the presence of a remarkably large 1208 Hz four-bond thallium−fluorine coupling constant in chloroform at room temperature, which is considerably larger than 878 Hz observed for the pyrazolyl borate analogue [MeB(3-(CF 3 )Pz) 3 ]Tl. Although [PhB(6-(CF 3 )Py) 3 ]Tl is structurally nonrigid at room temperature in chloroform, at lower temperatures, the ligand arm exchange slows down, revealing 4 J Tl−F = 1110 Hz. Steric demands of these ligands have been quantified using the buried volume concept. In addition, ligand transfer chemistry from [MeB(6-(CF 3 )Py) 3 ]Tl and [PhB(6-(CF 3 )Py) 3 ]Tl to copper(I) under ethylene and computational analyses of the various coordination modes of tris(pyrazolyl)borates and tris(pyridyl)borates are reported.

Going for gold – the chemistry of structurally authenticated gold(i)–ethylene complexes

“…This would also be observed later with B-phenyl substituted tris(pyridyl)borate complexes. 84,95,96 Despite the clear difference in coordinating and non-coordinating pyrazole arms in the crystal structure, only one set of resonances was observed in the 1 H, 13 C{ 1 H}, and 19 F NMR for the copper, silver, and gold complexes at room temperature, which is in agreement with the coordinational fluxionality of the donor arms of the tris(pyrazolyl)borate ligand in solution afforded by the flexibility of the tetrahedral boron linkage.…”