Synthesis of tris(pyrazolyl)methanes of unprecedented complexity and functionality

Solventless Synthesis of Poly(pyrazolyl)phenyl-methane Ligands and Thermal Transformation of Tris(3,5-dimethylpyrazol-1-yl)phenylmethane

The solventless synthesis of tris(pyrazolyl)phenylmethane ligands of formula C₆H₅C(Pz^R2)₃ (R = H, Me), starting from PhCCl₃ and 3,5-dimethylpyrazole (Pz^Me2) or pyrazole (Pz) was performed. The sterically crowded C₆H₅C(Pz^Me2)₃ is thermally transformed into the bis(pyrazolyl)(p-pyrazolyl)phenylmethane ligand Pz^Me2-C₆H₄CH(Pz^Me2)₂. In this compound both Pz^Me2 rings are linked through the N-atom to the methine C-atom. At higher temperatures, the binding mode of Pz^Me2 changes from N1 to C4. All transformations occurred via quinonoid carbocation intermediates that undergo an aromatic electrophilic substitution on the 4-position of Pz^Me2. Reaction conditions were established to obtain five tris(pyrazolyl)phenylmethane ligands in moderate to good yields. ¹H- and ¹³C-NMR spectroscopy and X-ray diffraction of single crystals support the proposed structures.

Tris(5-methyl-3-phenyl-1H-pyrazol-1-yl)methane

The first crystal structure of a second-generation tris­(pyrazol­yl)methane, namely the title compound, C₃₁H₂₈N₆, is reported. The mol­ecule exhibits a helical conformation with an average twist of 35.1°. In addition, there are C—H⋯π inter­actions of 3.202 (2) Å between the pyrazole C—H group and neighbouring phenyl groups.

Coordination, organometallic and related chemistry of tris(pyrazolyl)methane ligands

Tris(pyrazolyl)methanes are the neutral analogues of the widely exploited and highly useful tris(pyrazolyl)hydroborates, yet by comparison with their boron based counterparts their chemistry is underdeveloped. Recent breakthroughs in the synthesis of ring-substituted tris(pyrazolyl)methanes offer the opportunity for the development of this useful and promising class of ligand. This review summarises the current state of the coordination and organometallic chemistry of tris(pyrazolyl)methanes and highlights areas in which development is likely to occur.

Synthesis of a Macrobicycle Incorporating the Tris(pyrazolyl)methane Ligand

Steric crowding of the 3-position of tris(pyrazolyl)borate and -methane ligands has produced tetrahedral metal complexes with controlled reactivity. As an alternative, we propose to incorporate the tris(pyrazolyl)methane chelate in a macrobicyclic structure in order to create a cavity with well-defined dimensions and shape. Acid-catalyzed equilibration of excess of the new pyrazole 3-(1H-pyrazol-3-yl)benzenemethanethiol acetate with HC(3,5-Me(2)pz)(3) followed by hydrolysis affords a functionalized tris(pyrazolyl)methane, which reacts with 1,3,5-tris(bromomethyl)benzene in K(2)CO(3)/DMF to give the title compound. [structure: see text]