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Potassium tris(3,5 dimethyl 1 pyrazolyl)borate

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Appearance  White solid
Potassium tris(3,5-dimethyl-1-pyrazolyl)borate

Potassium tris(3,5-dimethyl-1-pyrazolyl)borate, abbreviated KTp*, is the potassium salt of the anion HB((CH3)2C3N2H)3. Tp* is a tripodal ligand that binds to a metal in a facial manner, more specifically a Scorpionate ligand. KTp* is a white crystalline solid that is soluble in polar solvents, including water and several alcohols.

Contents

Synthesis

KTp* is synthesized in a manner similar to that of KTp by the reaction of potassium borohydride and 3,5-dimethylpyrazole. Hydrogen gas is evolved as each of the pyrazole reacts at the boron. The rate of B-N bond formation becomes more difficult with each successive 3,5-dimethylpyrazolyl due to the increase in steric hindrance around the boron:

3 Me2C3N2H2 + KBH4 → KHB(Me2C3N2H)3 + 3 H2

The required dimethylpyrazole is obtained by condensation of hydrazine and acetylacetone.

Role as ligand

The active binding sites in Tp* are the three nitrogen centers that are not bonded to the boron. Although more weakly binding than cyclopentadienyl ligands, Tp* is still a tightly coordinating. The benefit of Tp* over its sister compound Tp is the addition of the methyl groups on the pyrazolyl rings, which increases the steric hindrance of the ligand enough that only one Tp* can bind to a metal. This leaves the remaining coordination sites available for catalysis.

References

Potassium tris(3,5-dimethyl-1-pyrazolyl)borate Wikipedia


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