Potassium tris(3,5-dimethyl-1-pyrazolyl)borate
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| Names | |
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IUPAC name
Potassium tri(3,5-dimethyl-1-pyrazolyl)borohydride
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| Other names
Tp* ligand
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| Identifiers | |
| ECHA InfoCard | 100.203.488 |
| Properties | |
| C15H22BKN6 | |
| Molar mass | 336.28 gmol−1 |
| Appearance | White solid |
| Melting point | 292 to 301 °C (558 to 574 °F; 565 to 574 K) |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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| Infobox references | |
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.
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:
The required dimethylpyrazole is obtained by condensation of hydrazine and acetylacetone.
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.
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