Pyrazolylborate Ligands Written with Jaclyn M. Murphy

Pyrazolylborate Ligands (Written with Dr. Jaclyn M. Murphy) 

CHAPTER 4 COVALENT (x-TYPE) LIGANDS BOUND THROUGH METAL-HETEEOATOM BONDS 

A comparison of the orientation of substituents in Tp and Cp derivatives. This figure is adapted from reference 227. 

The synthesis of Tp ligands that contain different substituents on the 3- and 5-positions on the pyrazole have been reported, For example, Graham and co-workers reported the synthesis of tris[3-(trifluoromethyl)-5-methyl]pyrazole borate. However, the most commonly used polypyrazolylborate ligands are substituted symmetrically at the 3- and 5-position. The unsymmetrical systems can undergo shifts of boron between the two nitrogens, and this shift scrambles the 3- and 5- positions.  

Complexes of these pyrazolyl groups are typically prepared by reaction of the metal halide with the anionic pyrazolyl ligand. For example, bis-olefin complexes of group 9 metals, such as rhodium and iridivtm, are prepared from complexes of the general type [M(olefin)2Cl]2, in which M = Ir and Rh, and olefin = ethylene, COE, COD, norbomadiene, etc., upon the addition of Tp salts (Equation 4.46). Although a majority of Tp complexes are obtained from the reaction of a metal halide with a salt of the anionic Tp ligand, some Tp complexes have been synthesized by alternate routes. For example, Tp VO(acac) 

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