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

Thallium(I) complexes of B-methylated and B-phenylated tris(pyridyl)borates featuring trifluoromethyl groups at the pyridyl ring 6-positions have been synthesized by metathesis using the corresponding potassium salts [MeB(6-(CF3)Py)3]K and [PhB(6-(CF3)Py)3]K with thallium(I) acetate. The closely related tris(pyrazolyl)borate analogue [PhB(3-(CF3)Pz)3]Tl has also been prepared, and comparisons of structural and spectroscopic features between the two scorpionate families are presented. [MeB(6-(CF3)Py)3]Tl displays κ3-coordination of the tris(pyridyl)borate similar to that of tris(pyrazolyl)borate in [MeB(3-(CF3)Pz)3]Tl, while [PhB(6-(CF3)Py)3]Tl and [PhB(3-(CF3)Pz)3]Tl feature κ2-N,N ligand coordination modes with the B-phenyl groups flanking the thallium sites. 19F NMR spectroscopy of [MeB(6-(CF3)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-(CF3)Pz)3]Tl. Although [PhB(6-(CF3)Py)3]Tl is structurally nonrigid at room temperature in chloroform, at lower temperatures, the ligand arm exchange slows down, revealing 4JTl-F = 1110 Hz. Steric demands of these ligands have been quantified using the buried volume concept. In addition, ligand transfer chemistry from [MeB(6-(CF3)Py)3]Tl and [PhB(6-(CF3)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.

In situ tracking and characterisation of scorpionate ligands via11B-NMR spectroscopy

Herein, we exemplify the use of ¹¹B-NMR spectroscopy as a new means of tracking the synthesis of scorpionate ligands in situ and ascertaining their purity upon isolation. We have demonstrated the use of the characterisation technique on five well known scorpionate ligands as their potassium salts.

Using ¹¹B-NMR spectroscopy for the in situ tracking and characterisation of the well known scorpionate ligand class. Five examples are included.

Bis- and Tris(2-oxobenzimidazolyl)hydroborato Complexes of Sodium and Thallium: New Classes of Bidentate and Tridentate Oxygen Donor Ligands

A series of bis- and tris(oxobenzimidazolyl)hydroborato compounds, namely, [Bo^RBenz]Na and [To^RBenz]-Na (R = Me, Bu^t, Ad), which feature uncommon sterically demanding LX [O₂] and L₂X [O₃] donor ligands, have been obtained via the reactions of NaBH₄ with 1-R-1,3-dihydro-2H-benzimidazol-2-ones. Evidence that the alkyl substituents are suitably located to have a significant impact on the coordination environment is provided by the observation that the methyl derivative [To^MeBenz]Na(κ³-diglyme) exhibits κ³-coordination of the diglyme, whereas the t-butyl and adamantyl derivatives, [To^ButBenz]Na(κ²-diglyme) and [To^AdBenz]Na(κ²-diglyme), exhibit κ²-coordination. The [Bo^RBenz] and [To^RBenz] ligands also allow for isolation of discrete mononuclear thallium compounds, [Bo^RBenz]Tl and [To^RBenz]Tl, for which the steric demands of the ligands have been quantified in terms of both cone angle and buried volume concepts.